1 the properties - richmondelt.comrichmondelt.com/su_2018/sec/pathwaytochemistry_sb.pdf · ge to...

4 Pathway to Chemistry

Everything that has mass and volume is matter: the book you’re reading, the chair you’re sitting on and even the air you’re breathing.

All matter is made up of small particles or building block units called atoms. These atoms, in turn, are made up of even smaller, subatomic particles called electrons, protons and neutrons. Protons and neutrons are found in the central part of each atom, called the nucleus, and electrons constantly spin around the nucleus in a space known as an atomic shell, or electron shell.

There are 98 kinds of naturally occurring atoms, or elements, as well as several others that occur only under laboratory conditions. An element is a pure substance made of one kind of atom. An atom is the smallest particle of an element that maintains the characteristic properties of the element, and the atoms of each element are distinct from those of other elements. What makes each element distinct is the number of subatomic particles found in its atoms. The periodic table is a tool used by chemists to classify these elements into groups according to their properties and atomic structure. Scientists can tell the characteristics of a certain element by looking at its position in the periodic table.

We identify people based on certain characteristics, or properties such as their voice, fingerprints or DNA. This also

applies to elements. Each element has certain physical and chemical properties. Physical properties can be observed or measured without causing any change to the identity of the matter. They include color, odor, shape, mass, volume, melting point and others. Chemical properties determine how a substance reacts with others and whether or not it will join, or bond, with them. Simple observation is not enough to know a substance’s chemical properties.

A particular element can exist in several forms, and each form may have different physical and chemical properties: graphite and diamond, for example, are both made of the same element, carbon, but have very different physical and chemical properties.

Few elements exist in nature in pure form. Most substances are in fact

compounds. A compound is a substance made up of two

or more different elements chemica l l y bonded together. Chemical bonds form between the electrons in the outer shells of atoms.

Most things are a mixture of different c o m p o u n d s a n d

elements. Such mixtures can often be separated

by using the properties of the individual substances that

make them up.

1

Key Wordsatom (n) – the smallest particle of an element that maintains the element’s propertiescompound (n) – a substance made of two or more elements chemically bonded together element (n) – a substance made of one type of atommatter (n) – anything that has both mass and volumeperiodic table (n) – a table of chemical elements grouped according to their properties and showing their symbol, atomic number and atomic massproperty (n) – a quality or an attribute, such as appearance or behavior, that characterizes members of a group as a whole

Matter and Its Properties

Key Concepts ❯ All matter is made up of atoms, and atoms are made up of smaller subatomic particles. ❯ There are over a hundred different types of atoms; we call these elements. ❯ Properties are characteristics used to distinguish different types of matter. ❯ Properties of matter are grouped into two categories: physical and chemical.

THE Properties OF Matter

❯❯Unit

❯ The Sun consists mainly of the elements helium and hydrogen; hydrogen is the lightest and most abundant element in the universe.

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❯ Matter is defi ned as anything that has mass and volume, like this orange, for example.

nts. Each element cal and chemicalal properties can easured without ge to the identity ey include color, , volume, melting Chemical properties substance reacts with er or not it will join, or Simple observation is not a substance’s chemical

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❯ Matter is defi ned as anything that has mass and volume, like this orange, for example.

patway to Chemistry unit1.indd 4patway to Chemistry unit1.indd 4 1/19/15 3:08 PM1/19/15 3:08 PM

Unit 1 The Properties of Matter 5

❯ Observe and Question

1 Read the text and answer the questions.

a. How are elements and compounds similar? How are they different?

b. Why is the periodic table a useful tool for scientists?

c. Name some physical properties of elements.

d. How are chemical properties different from physical properties?

2 Look at the picture. Select one of the objects and describe its properties so that a classmate can identify it. Did you use physical or chemical properties to describe the object? Explain why you used those particular properties.

3 Write the properties that you would use to separate the fruit in the bowl. Are these properties physical or chemical? Explain.



❯ Topic

Key Wordsatomic mass (n) – the number of protons and neutrons in the nucleus of an element’s atomatomic number (n) – the number of protons in the nucleus of an element’s atombrittle (adj) – easily broken luster (n) – the way a substance refl ects lightmetal (n) – a substance that is usually shiny, can be melted and shaped, and is a good conductor of electricity and heatmetalloid (n) – a substance that shares some characteristics of a metal and some of a nonmetal nonmetal (n) – a substance that doesn’t have metallic properties

The periodic table is a chart that lists the elements based on the structure of their atoms. Russian chemist Dmitri Mendeleev

devised the first periodic table in 1869 using the 63 elements known at the time. He based his table on each element’s atomic mass, which increases across the table and depends on the number of protons and neutrons in the nucleus of the element’s atom. He also arranged the elements in columns according to their properties.

Today’s periodic table is similar, but it is organized in order of increasing atomic number, which depends on only the number of protons in the nucleus. The table is called a periodic table because of the repeating, or periodic, pattern of properties of the elements. The rows of the table are called periods, and each element in a period has the same number of electron shells. The fi rst electron shell contains two electrons, so the fi rst period contains only two elements: hydrogen and helium. The second and third electron shells have eight electrons each, so there are eight elements in each of these periods, and so on. The columns are called groups. Elements in a group share similar properties and have the same number of electrons in their outer shells. The electrons in the outer shell are involved in the forming and breaking of chemical bonds during chemical reactions; the number of electrons in the outer shell determines how reactive an element is and which other elements it will react with. There are 18 groups in the periodic table. The elements in group 18 are noble gases and have a full

outer shell of electrons, so they aren’t very reactive.

The periodic table divides the elements into metals, nonmetals and metalloids. Most of the elements are metals. All the elements to the left of the elements in green in the periodic table above (except hydrogen) are classified as metals. Most metals are shiny, dense and conduct heat and electricity well. They are also malleable (they can be beaten into fl at sheets), as well as ductile (they can be stretched into wire). The elements in the darker shade of green are metalloids, which share some properties with metals and some with nonmetals. The rest of the elements, along with hydrogen, are classifi ed as nonmetals. When nonmetals are solids, they are brittle and don’t conduct heat and electricity well. Unlike metals, they don’t have a metallic luster.

Objective Organize elements into groups and periods in the periodic table

Key Concepts ❯ The periodic table arranges elements in columns, called groups; the elements in each group contain the same number of electrons in their outer shells. ❯ Elements in each group have similar properties, which are related to the number of outer shell electrons. ❯ Compounds are not included in the periodic table because they consist of two or more different elements joined together by chemical bonds.

❯ The periodic table shows each element’s chemical symbol, name, atomic number and atomic mass.

Exploring the Periodic Table1

The PeriodicTable of Elements





a. Describe how the periodic table is organized.

b. What do the elements in each group have in common?

c. What do the elements in each period have in common?

d. What are some common properties associated with metals?

e. What are some common properties associated with nonmetals?

f. Write why you think the periodic table is useful for scientists.

❯ Research

Supplies

❯ periodic table (see page 91) ❯ instruction cards (see pages 93 and 95) ❯ colored pencils or pens

Procedure

1 Get to know the periodic table.

a. Work in groups of three. b. Put the instruction cards on different tables around the room.c. Read the instructions on the cards and color your periodic table as instructed.


Pathway to Chemistry 8

❯ Analyze

1 What are the three main categories of elements in the periodic table?

2 Complete the sentences.

a. Most of the elements in the periodic table are .

b. The elements immediately to the right of the zigzag line are .

c. The elements in the upper right corner are .

3 Answer the questions.

a. Where are the noble gases in the periodic table? What two properties do they have in common?

b. Where are the alkali metals in the periodic table? What two properties do they have in common?

c. Fluorine is a member of the halogen group. What are some other halogens?

d. Where would you expect to fi nd elements with the biggest atoms?

e. Where would you put element 119 and why?

4 Write two trends you can see in the table as you go from left to right.

5 What other ways could you list and organize the elements?



❯ Topic 2

Objective Determine if pairs of elements form ionic or covalent bonds

Key Concepts ❯ There are two types of chemical bonds: covalent bonds and ionic bonds. ❯ A covalent bond forms when the atoms of two nonmetals share a pair of electrons and become a molecule; in this way, the outer shell of each atom is fi lled with electrons. ❯ Diatomic molecules are formed by two atoms of the same element, such as oxygen, hydrogen or nitrogen. ❯ An atom can gain or lose electrons in order to have a full outer shell of electrons; the atom then becomes a charged particle called an ion. ❯ Hydrogen atoms and metal atoms can lose electrons to form positively charged ions; nonmetal atoms can gain electrons to form negatively charged ions. ❯ Ionic bonds form as a result of the electrical attraction between ions with opposite charges.

Defi ning Chemical Bonding

Key Wordscovalent bond (n) – a chemical bond between two atoms that share electronsion (n) – an atom or a molecule that has gained or lost one or more electrons, giving it a net positive or negative electric chargeionic bond (n) – a chemical bond formed by the electrical attraction between two ions with opposite chargesionic compound (n) – a compound formed as a result of ionic bondingmolecule (n) – a covalent compound formed as a result of covalent bonding between nonmetal atoms

❯ In covalent bonding, the electrons (in red) of different nonmetal atoms combine to complete each other’s outer electron shells and make a stable molecule.

Covalent and Ionic Bonding

When two atoms join together, they form a chemical bond. A chemical bond usually involves the transfer or

sharing of one or more electrons. In general, atoms tend to gain or lose electrons so that their outer shell has eight electrons because this confi guration makes them more stable.

Not all chemical bonds are alike. One type of chemical bond is a covalent bond. This occurs when atoms of nonmetals form a molecule by sharing a pair of electrons in their outer shells. When the atoms are of the same element, a diatomic molecule forms. The fi rst two lines of the diagram below show diatomic molecules of hydrogen (H) and chlorine (Cl). When the atoms are of different elements, a covalent compound is formed, such as hydrogen chloride (hydrochloric acid), shown in the third line of the diagram. A molecule is the smallest particle of a compound that maintains the compound’s properties.

Another type of chemical bond is an ionic bond. When a metal joins with a nonmetal, such as sodium with chlorine, they form an ionic compound. Table salt (see diagram below) is an example of an ionic compound. The metal and nonmetal atoms in an ionic compound do not share electrons. Instead, the nonmetal atoms take one or more electrons from the metal atom. When an atom gains or loses electrons, it forms a charged particle called an ion. In table salt, each sodium atom loses the single electron in its outer shell and becomes a positively charged ion (Na+). And each chlorine atom, with seven electrons in its outer shell, gains an electron and forms a negatively charged ion (Cl–). This leaves both atoms with a full outer shell of electrons. The oppositely charged ions attract each other and form an ionic bond. The chemical formula for this ionic compound is NaCl, and its chemical name is sodium chloride.

❯ Ionic bonds form as a result of the attraction between oppositely charged ions. In sodium chloride, each sodium atom loses an electron and becomes a positively charged ion, and each chlorine atom gains an electron and becomes a negatively charged ion.

Na + Cl Na+ + Cl –

forming ionic bond

H + H H H or H–H

Cl + Cl Cl Cl or Cl–Cl

H + Cl H Cl or H–Cl

forming covalent bond




1 Read the text and look at the diagrams. Then draw a diagram of a water molecule.

a. Water is a compound of two nonmetals, hydrogen and oxygen. Hydrogen has one electron in its outer shell, and oxygen has six electrons in its outer shell. Draw a diagram to show how two hydrogen atoms and one oxygen atom bond to form a water molecule.

2 Look at the diagram and answer the questions about how magnesium and oxygen form an ionic compound.

forming ionic bond

Mg + O Mg2+ + O 2–

a. How many electrons does magnesium have in its outer shell? How many does oxygen have?

b. Explain why each ion in the compound has the charge shown.

3 Look at the diagram. Explain why two chlorine atoms bond with only one calcium atom.

Ca + Cl + Cl Ca2+ + Cl – + Cl

–



❯ Research

Supplies

❯ paper ❯ masking tape

❯ stopwatch ❯ marker pen

❯ periodic table (see page 97)

Procedure

1 Explore the electron confi guration of elements.

a. Get into groups of 8.b. In your group, write the symbols for the following elements on pieces of masking

tape to make name tags: Li, Na, Ca, Cl, O, H, Ne, Al.c. Stick one of the name tags on your chest. d. Draw the electron confi guration of your element on a piece of paper. Refer to the

periodic table for help. Remember, atoms always have the same number of electrons and protons, and the atomic number of an element tells you how many protons there are in its atoms. The period of an element tells you how many electron shells it has, and the group of an element tells you how many electrons are in its outer shell.

2 Explore ionic bonding between metal and nonmetal elements.

a. In your groups, line up four desks end-to-end and put a row of four chairs on either side so that the chairs are facing each other.

b. Put four sheets of paper on each desk. Students with metal elements sit along one row of desks. Students with nonmetal elements sit facing them.

c. If your element and the element of the student in front of you are compatible for ionic bonding, try to draw how the compound forms.

d. After a few minutes, students with nonmetal elements change places. e. Continue until all the possible bonds between these metal and nonmetal elements

have been drawn.

3 Replace the metal elements.

a. If you have a metal element, replace it with one of these elements: Cl, O, H, Ne. Write the symbol of the element on a piece of masking tape and stick it to your chest.

b. Do the same activity again, changing places until you have sat in front of each of the other nonmetal elements. If a pair of elements can form a covalent bond, try to draw how it forms.

❯ Analyze

1 Which elements formed covalent bonds?

2 Which elements formed ionic bonds?



3 Find the most stable bonding partner for sodium.

a. Read the description of sodium and draw its electron confi guration in the fi rst set of concentric circles.

11Na

Sodium23

Sodium is lustrous, or shiny. Due to its tendency to lose electrons, it

is highly reactive, even explosive, if it gets near water or oxygen.

b. Read the descriptions of lithium, calcium and fl uorine and draw their electron confi gurations.

3Li

Lithium7

Lithium is a highly reactive metal that tends to lose electrons.

20Ca

Calcium40

Calcium is a reactive metal that tends to lose electrons.

9F

Fluorine19

Fluorine is a nonmetal that tends to gain electrons.

c. Which of these elements will form the most stable bond with sodium? Draw the bond alongside sodium above.

d. Compare sodium and the bonding partner you chose for it. Write similarities and differences.

4 Find the most stable bonding partner for oxygen.

a. Read the description of oxygen and draw its electron confi guration in the fi rst diagram.

8O

Oxygen16

Oxygen is a nonmetal that, like all nonmetals, tends to gain electrons.



b. Read the descriptions of boron, magnesium and phosphorus and draw their electron confi gurations.

5B

Boron11

Boron is a metalloid that tends to gain electrons.

12Mg

Magnesium40

Magnesium is a reactive metal that tends to lose electrons.

15P

Phosphorus19

Phosphorus is a nonmetal that tends to gain electrons.

c. Which element will form the most stable bond with oxygen? Draw the bond alongside oxygen on the previous page.

d. Compare oxygen and the bonding partner you chose for it. Write similarities and differences.

5 Draw the electron confi guration of neon and answer the question.

10Ne

Neon20

a. Does neon readily form bonds with other elements? Explain.

6 Draw the electron confi guration of aluminum and answer the question.

13Al

Aluminum27

a. Aluminum is highly reactive and gives its electrons away very easily. Which elements can aluminum readily form bonds with and why?



❯ Topic

How Is Matter Classifi ed?

Substances in which each particle is alike are called pure substances. Elements and compounds, for example, are both pure substances.

We already know that an atom is the smallest particle of an element that keeps the properties of that element. A few elements, such as gold, copper and silver, can exist in nature as single atoms. The atoms of most elements, however, never exist alone in nature and instead bond chemically with other atoms.

When a nonmetal atom combines with another atom of the same element, they form a diatomic molecule. For example, two atoms of oxygen, chorine or hydrogen combine to form diatomic molecules of oxygen (O

2),

chlorine (Cl2) or hydrogen (H

2), all

of which exist under normal conditions as gases.

Compounds are pure substances made of two or more different

elements. Compounds of nonmetal atoms form molecules, and compounds of metal atoms and nonmetal atoms form ions.

Each compound has a specific ratio of its elements and a specifi c chemical formula. A water molecule, for instance, contains two hydrogen atoms and

one oxygen atom combined by a covalent bond. The chemical formula H

2O, therefore,

is used to represent water. Table salt contains one sodium atom and one chlorine atom joined by an ionic bond. The formula for table salt, or sodium chloride, is NaCl.

Substances made up of different types of elements and compounds are called mixtures. Mixtures can be divided into two basic types. A homogeneous mixture is a uniform mixture, so its individual parts are not visible. Examples of homogeneous mixtures include blood, air and even steel. A heterogeneous mixture, on the other hand, has a variable composition and does not look uniform. Examples include soil, salad dressing and smog. The components of mixtures can often be separated based on their individual properties.

Key Wordsheterogeneous (adj) – not uniform in structure or compositionhomogeneous (adj) – uniform in structure or compositionmixture (n) – a combination of two or more substances that maintain their chemical properties and don’t form bondspure substance (n) – matter that can’t be separated into simpler components without chemical change

Objective Distinguish between an element, a compound and a mixture

Key Concepts ❯ Each element in the periodic table has a chemical symbol. ❯ Atoms of a particular element are identical to each other. ❯ Compounds have specifi c chemical formulas and form when two or more atoms join by chemical bonds. Some compounds are molecules, while others form between ions. ❯ A mixture consists of a combination of elements and compounds that don’t form chemical bonds. ❯ The components of mixtures can often be separated based on their individual properties.

3

Distinguishing Elements, Compounds and Mixtures

❯

Diagram showing the classifi cation of matter

❯ Gold, one of the few elements that can exist in nature as a single atom, is the most malleable element.

ter Classifi ed?ach particle is

substances. pounds, for re substances. atom is the

nt that keeps ment. A fewer and silver, e atoms. The wever, never nstead bond

ombines with ent, they form ple, two atoms en combine to oxygen (O

2),

drogen (H2), all

under normal gases. nds are pure

one oxygen atom combined by a covalent bond. The chemical formula H

2O, therefore,

is used to represent water. Table salt contains one sodium atom and one chlorine Key Words

❯

Diagram showing the classifi cation of matter

Matter

HomogeneousMixture

HeterogeneousMixture

PureSubstance

Mixture

CompoundElement

Elements and comexample, are both pu

We already know that ansmallest particle of an elemethe properties of that elemelements, such as gold, coppcan exist in nature as singlatoms of most elements, hoexist alone in nature and chemically with other atoms.

When a nonmetal atom canother atom of the same elema diatomic molecule. For examof oxygen, chorine or hydrogform diatomic molecules of

chlorine (Cl2) or hyd

of which existcocccc nditions as

Compousubstancetwo or m

elementsof nonform mcompouatoms aatoms

Each coa specificelementschemicalwater minstance, hydrogen

❯ Gold, one of the few elements that can exist in nature as a single atom, is the most malleable element.




1 Read the text and complete the table. Refer to the periodic table on page 97 for the correct chemical symbols.

a. Write the chemical formula for each kind of matter.

Matter Chemical SymbolElement or Compound

Molecule or Ion

Oxygen gas

Silver

Table salt

Gold

Water

Chlorine gas

Hydrogen gas

Copper

b. Write E (if they are elements) or C (if they are compounds).c. Write M (if the compounds are molecules) or I (if they form ions).

2 What property do elements and compounds have in common? How are they different from mixtures?

3 Look at the pictures. Answer the question.

a. Which picture represents a heterogeneous mixture and which represents a homogeneous mixture? Explain.

❯ Lemonade ❯ Trail mix❯ Lemonade ❯ Trail mix



❯ Research

Supplies

❯ table (see page 99) ❯ substance cards (see pages 101 and 103) ❯ 20 small jars or bottles ❯ copper wire ❯ steel object (e.g., a ball-bearing)

❯ silver object (e.g., an earring)

❯ iron object (e.g., a nail) ❯ charcoal ❯ chalk ❯ vinegar

❯ baking soda ❯ aluminum foil ❯ sugar ❯ cream of tartar ❯ black pepper ❯ lemon juice

❯ Epsom salt ❯ honey ❯ soil ❯ salt ❯ water ❯ sand

Procedure

1 Prepare the cards.

a. Put a substance in each of the jars. Leave the jar for air empty.b. Turn to pages 99–103 and cut out the table and the substance cards. c. Spread the substance cards around the room and place the jars with the

corresponding substances beside them.d. Visit each station and complete your table. You have two or three minutes at each

station.

❯ Analyze

1 Answer the questions.

a. Were you unsure if any substances were elements, compounds or mixtures? Which?

b. Discuss with your classmates how you could distinguish between the elements, compounds and mixtures. Write your conclusions.

2 Write other examples of each type of substance.

a. Elements:

b. Compounds:

c. Mixtures:



❯ Topic

Key Wordscrystallization (n) – a process that separates a solid from a liquidevaporate (v) – to change from a liquid to a gasfi ltration (n) – the removal of insoluble particles from a fl uid by passing the fl uid through a porous materialinsoluble (adj) – not solublesoluble (adj) – able to dissolve in another substancesolute (n) – a substance dissolved in another substancesolution (n) – a liquid containing dissolved substances solvent (n) – a liquid in which another substance can be dissolved

Most things in the world around us are mixtures. Soil, s e a w a t e r

and air, for example, are all types of mixtures. Unlike the substances in a compound, the substances in a mixture are not held together by chemical bonds; each substance in a mixture keeps its own properties.

It’s easy to separate a heterogeneous mixture because you can see the different parts. If you don’t like tomatoes, for example, it’s easy just to pick them out of a salad. Soil can also be easily separated. It consists of materials such as rocks, sand, clay and decaying leaves, and to separate this mixture of different-sized solids, all you have to do is pour the soil through sieves with smaller and smaller holes. Archaeologists often use this method to fi nd small pieces of pottery or bones, as do gold prospectors when searching for gold.

In homogeneous mixtures, however, you can’t see the different parts that make up the mixture. Seawater is one such example. You can’t see the different substances in seawater because their particles are so evenly spread out. Lemonade, likewise, is a uniform

mixture of lemon juice, water and sugar. These types of mixtures are called

solutions. In both seawater and lemonade, other substances

have dissolved in water. A substance that dissolves in another substance is called a solute. The substance that a solute dissolves in is called a solvent. Usually,

the solvent is a liquid such as water; the solute can

be a liquid, a solid or a gas. Water is known as the universal

solvent because of its ability to dissolve so many other substances.

Lemon juice and sugar both dissolve in water and are therefore described as soluble. If you put sand

into water, however, it will not dissolve: it is insoluble. Filtration can separate a mixture of a solvent and an insoluble solid. The solvent will pass through the fi lter paper but the insoluble solid will not. But fi ltration cannot separate soluble substances from water. Instead, you can often separate a solid solute (such as sugar) from a solvent (such as water) by letting the solution sit until the liquid evaporates. When it evaporates, the solid’s crystals will be left behind. This process is known as crystallization. This method works with water, but not all solvents evaporate so readily.

Filtration, Evaporation and Crystallization

4Separating Substances by Filtration, Evaporation and CrystallizationObjective Separate sodium chloride from seawater and sand

Key Concepts ❯ A solute dissolves in a solvent to form a solution. ❯ The solvent is usually a liquid, and the solute can be a solid, liquid or gas. ❯ An insoluble substance does not dissolve in a solvent. ❯ Insoluble substances can be removed from a solution by fi ltration. ❯ Soluble substances can be removed from a solution by evaporation and crystallization.

❯ Panning for gold in a heterogeneous mixture of sand

❯ Seawater contains ions of chloride, sodium, sulfate, magnesium, calcium, potassium and bicarbonate. These ions, as well as the hydrogen and oxygen of water, make up 99.9% of seawater.

❯ Seawater contains ions of chloride, sodium, sulfate, magnesium, calcium, potassium and bicarbonate These





a. What is the difference between a homogeneous mixture and a heterogeneous mixture? Give examples.

b. What kind of mixture is a solution? How can you separate the solute from the solvent?

c. How can you separate a mixture of gravel, sand, silt and clay?

d. A student mixes sugar into hot water until no more sugar will dissolve. She pours some of the solution into a shallow pan. A few days later, the pan has particles of sugar on the bottom but no water. Explain what happened.

e. Name three solids that dissolve in water.

❯ Research

Supplies

❯ coffee fi lter ❯ 50 grams of sand ❯ measuring jug ❯ pan ❯ tablespoon

❯ stove top ❯ 1/2 liter of water ❯ Pyrex mixing bowl ❯ small bowl ❯ funnel

❯ kettle ❯ weighing scale ❯ wooden spoon ❯ 50 grams of table salt

Procedure

1 Do an experiment to separate insoluble and soluble substances from a liquid. First, prepare the salt and sand solution.

a. Boil half a liter of water in the kettle. Measure 250 milliliters of the boiling water in the measuring jug and pour it into the mixing bowl. The boiling water is your solvent.

b. Weigh the small bowl on the scale and record its mass in the table on the next page. Then weigh out 50 grams of salt and put it in the small bowl.

c. Add the salt to the boiling water in the mixing bowl and stir with the wooden spoon until the salt dissolves.

d. Weigh out 50 grams of sand and then stir it into the mixing bowl.



2 Filter the solution.

a. Put a coffee fi lter in the funnel. Pour the mixture through the coffee fi lter and into the pan. This will remove the insoluble substance (the sand).

3 Evaporate the solution.

a. Place the pan on the stove and heat it gently while stirring until only around fi ve percent of the solution is left.

4 Crystallize the salt from the remaining solution.

a. Leave the pan by a window until all the remaining water has evaporated.b. Scrape the salt from the bottom of the pan onto a piece of fi lter paper and weigh it to

see how much salt has been reclaimed from the solution.

Results

1 Complete the table with the measurements you make during the experiment.

Activity Mass (g)

Mass of small bowl

Initial mass of salt 50

Mass of salt reclaimed after fi ltration, evaporation and crystallization

Percentage of salt reclaimed: (mass of salt reclaimed ÷ mass of salt dissolved) × 100

❯ Analyze

1 Did you reclaim the same mass of salt that you started with? Explain.

2 How could you make the procedure more effi cient?

3 Why did the fi lter remove the sand but not the salt?



❯ Topic

Key Wordscapillary action (n) – the tendency of a liquid to fl ow into a porous materialpolar molecule (n) – a molecule that has a slight positive charge on one end and a slight negative charge on the other

Paper Chromatography

Objective Use chromatography to separate soluble substances

Key Concepts ❯ The components of some solutions can be separated based on their individual properties by using chromatography. ❯ The colored solutes in liquids such as inks, dyes, pigments and food coloring can be separated in this way. ❯ A drop of the liquid is placed on a strip of paper, and the bottom of the strip is placed in a solvent; as the solvent spreads up the paper, the solutes in the liquid move at different rates and are separated.

Separating Mixtures by Chromatography

5

The word “chromatography” comes from the Latin for “to write with color.” It refers to the method used to separate different solutes from a

solution so that they can be identifi ed and studied.

Chromatography has two components, or phases: a moving phase (the solvent and the mixture of solutes it is carrying) and a stationary phase (the paper). As the solvent moves up into the paper, the paper absorbs and slows down the solutes at different rates: some solutes are attracted more strongly to the paper and are deposited quickly, and other solutes travel further up the paper. Chromatography can separate out tiny amounts of solutes, which is why it is often used in crime laboratories. For example, forensic detectives use it to separate drugs from urine and blood, to test paints or to help identify inks from pens used in crimes such as forgery. The technique is also used for chemical analysis in scientifi c research, medical testing and industrial processes.

The solvent used in chromatography depends on the type of solutes. Water, the universal solvent, has excellent dissolving properties because it is a polar molecule: each molecule has a slight negative charge near its oxygen atom and a slight positive charge near its hydrogen atoms. These charges help the water molecule attract other water molecules as well as polar solutes. Other common solvents include ethanol, vinegar and hexane.

During chromatography, a piece of paper is dipped in a liquid solvent, and the solvent moves up the pores in the paper by means of capillary action. The liquid can move up the paper against the force of gravity due to the molecular forces of attraction within the liquid and between the liquid and the inner surface of the pores. You can see this effect at the edge of a glass of water, where the water adheres to the glass and rises slightly above the rest of the liquid. The distance traveled by each solute varies according to how strongly it is attracted to the paper. As the different components of the mixture are carried along at different rates, they are deposited and separate out into bands of color on the paper’s surface.

❯ A simple chromatography setup❯ A simple chromatography setup

paper

water

ink spot

beaker

Before After





a. What is the moving phase in paper chromatography?

b. What is the stationary phase?

c. What kinds of mixtures is chromatography used to separate?

d. In what fi elds is chromatography commonly used?

e. Name one use you can think of for chromatography.

2 Water is known as the “universal solvent.” How does its bond help explain why water is able to dissolve so many different solutes?

3 Explain the role of capillary action in the separation of mixtures by paper chromatography.

❯ Research

Supplies

❯ 5 different black pens (e.g., permanent marker, boardmarker, normal marker pen, biro, fi ne point permanent pen) ❯ 5 coffee fi lters ❯ 5 glass jars or beakers

❯ adhesive tape ❯ pencil ❯ scissors ❯ water

Procedure

1 Do an experiment to separate the colored compounds in the ink of different types of pen.

a. Imagine you are an investigator at a crime scene. You fi nd a note written by the criminal. If you can identify what kind of pen was used, you will catch the criminal.

b. Your teacher will show you a chromatography sample from the pen used in the crime.



2 Using chromatography, identify which pen has the most similar ink to the ink used at the crime scene.

a. From the center of the coffee fi lter, make two cuts almost to the edge and at an angle of about 60 degrees to create a wedge.

b. Draw a dot with one of the pens near the thin end of the wedge. c. Using a pencil, label the fi lter paper with the name of the type of pen.d. Pour about two centimeters of water into a jar. Place the fi lter paper on top of the jar

and bend the wedge down so its tip is in the water. The dot should be above the water. e. Put the jar to one side and observe. The water will spread the black ink up the paper

and into its constituent colors.f. Repeat the steps for the four other pens.

❯ Analyze

1 Which pen matched the sample of the crime scene?

2 What evidence supports your hypothesis?

3 How could chromatography help solve a real crime?



❯ Topic

Key Wordscondense (v) – to change from a gas to a liquiddesalination (n) – the process of removing salt from waterdistillation (n) – the purifi cation of a liquid by evaporation and condensation solar still (n) – a device used to distill watervapor (n) – water in a gas state

Distillation of Seawater

Objective Purify salt water

Key Concepts ❯ Desalination is the removal of salt from water. ❯ There is too much salt in seawater to be processed by the human body. ❯ The kidneys excrete excess salt from the body as urine. ❯ Seawater is saltier than urine; this means that if you drink seawater, you need even more water to excrete the salt in it, and you quickly become dehydrated. ❯ One method of removing salt from water is by distillation. ❯ Man-made distillation systems use similar processes to those that occur in the water cycle.

Purifying Seawater by Distillation

6

Are you thirsty? How about a nice cold glass of seawater? Not a good idea. People cannot survive on seawater alone because it is

too salty. Human kidneys can only make urine that is less salty than seawater. Therefore, to get rid of all the excess salt taken in by drinking seawater, you would have to urinate more water than you drank. That’s not possible, so eventually you would die of dehydration even as you became thirstier.

Seawater, however, can be turned into drinking water through the process of desalination—the purifi cation of water by removal of the salt. Once the salt is removed from seawater, the water is safe to drink. In nature, desalination occurs during the water cycle. Heat from the Sun causes water, but not salt or other impurities, to evaporate from oceans. The pure water vapor rises, comes in contact with cooler air and then condenses to form clouds before falling as rain or snow. Solar desalination is the process responsible for the majority of fresh water on Earth.

Distillation, which mimics this natural process, is one method of separating liquid mixtures. When the mixture is heated, the substance with the lowest boiling point evaporates fi rst. This vapor then condenses and becomes a pure liquid. With seawater, the water evaporates but impurities, such as the salt, do not. The vapor then condenses to

become pure, or distilled, water. In a solar still, like the one in the diagram above, impure water is collected in a base, where it is evaporated by sunlight shining through a sheet of clear plastic. The pure water vapor condenses on the inside of the plastic and drips down the sides into the rim. It then leaves the rim via a tube and accumulates in a container. The resulting fresh water is safe to drink.

Distillation is one of the earliest forms of water treatment and is still used throughout the world today. In ancient times, many civilizations used this process on their ships to convert seawater into drinking water. Today, desalination plants are used to convert seawater to drinking water on ships and in many dry regions of the world.

❯ A wind-powered desalination plant

on of Seawater

e the salt in it, and you quickly becving salt from water is by distillation.systems use similar processes to those that occur in the water cycle.

y? How about a nice of seawater? Not a eople cannot survive

alone because it is eys can only make y than seawater.

all the excess ng seawater, nate more k. That’s

ually you on even .can be water

ess of rifi cation of the salt. moved from fe to drink. In nature, ring the water cycle. es water, but not salt

vaporate from oceans. ises, comes in contact

n condenses to form rain or snow. Solar

become pure, or distilled, water. In a solar still, like the one in the diagram above, impure water is collected in a base, where it is evaporated by sunlight shining through a sheet of clear plastic. The pure water vapor condenses on the inside of the plastic and drips down the sides into the rim. It then leaves the

❯ A solar still for separating fresh water from seawater

container for purifi ed water

sunlight

evaporation

condensation





a. Why can’t people drink seawater?

b. Describe the process of desalination.

c. Is the process a physical or a chemical change? Why?

2 Look at a world map. Select three places where desalination could increase the amount of fresh water available to people. Give reasons for your choices.

3 Look at the picture of another type of solar still, one that utilizes water evaporating from the ground. Describe how it works.

stones

sunlight

plastic sheet

distilled water

soil

evaporation

condensation



❯ Research

1 Watch Video 1. Then prepare your supplies.

Supplies

❯ plastic bottles of different sizes ❯ large resealable plastic bags ❯ large plastic containers with lids ❯ drinking glasses ❯ 1 liter of water ❯ duct tape ❯ straws

❯ sand ❯ adhesive tape ❯ plastic wrap ❯ squares of muslin ❯ aluminum foil ❯ 35 grams of salt ❯ scissors

❯ bowls ❯ measuring jug ❯ poster paper ❯ string ❯ marker pen ❯ weighing scale

Procedure

1 Prepare the simulated seawater.

a. Get in groups of no more than fi ve students.b. Weigh 35 grams of salt on the scale and measure 1 liter of water with the measuring

jug.c. Pour the water in a bowl and dissolve the salt in the water.d. Add a handful of sand and stir well.

2 Use any or all of the supplies to purify as much of the seawater as possible.

a. You have two classes to design and construct a device with the available supplies to purify as much seawater as possible.

b. Measure how much pure water you reclaimed from the seawater in the measuring jug.c. The team that purifi es the most water wins... and survives!

3 Make a poster explaining the steps and equipment you used to purify the water and present it to the class.

❯ Analyze

1 How much water did you manage to purify?

2 How could you improve your method to purify more water?

3 What other items would be useful to purify water?

4 Do you think you could survive on a desert island with no fresh water? Explain.



❯ Topic

Key Wordsbuoyancy (n) – the upward force that a fl uid exerts on an object, such as water on a boatconductivity (n) – the ability of a substance to conduct heat or electricityductility (n) – the ability of a substance to be stretched into wire or shaped without breakingfl ammability (n) – the ability of a substance to burnmagnetism (n) – the ability of a substance to be attracted to a magnetmalleability (n) –the ability of an object to be bent or shaped without breakingreactivity (n) – the tendency of a substance to react with other substancessolubility (n) – the ability of a substance to dissolve in a solvent to form a homogeneous mixture

Physical and Chemical Properties

Objective Investigate the physical properties of substances

Key Concepts ❯ The physical properties of a substance can be observed and measured without changing its composition. ❯ Physical properties include odor, color, density, solubility, magnetism, boiling point and melting point, among others. ❯ Physical properties can be used to describe and identify substances; for example, a colorless, odorless liquid that freezes at 0°C is probably water. ❯ To observe the chemical properties of a substance, the substance has to undergo a change to its composition. ❯ Examples of chemical properties include fl ammability and the tendency to rust or to react with other substances.

Defi ning Physical and Chemical Properties

7

❯ A car rusting and a match lighting are examples of chemical reactions.

Recall that physical properties of a substance can be observed or measured without changing its composition. These properties

can be classified into two groups: those that depend on the amount of matter in the sample, such as mass, weight, volume, density and size; and those that are independent of the amount of matter, such as color, odor, luster, malleability, ductility, freezing and boiling points, hardness and physical state.

Many of these physical properties can help identify a substance. Mass and volume depend on the size of the sample, but the ratio of mass to volume, or density, relates directly to the identity of the substance. The density of a substance is commonly compared to the density of water (1 g/cm3). Mass, which is the amount of matter in an object, is measured with a weighing scale. Volume, which is the amount of space an object occupies, can be measured with a ruler if the object has a regular shape; if the object has an irregular shape—a rock or a key, for example—its volume can be measured by water displacement. With this method, the object is dropped into water and the water level rises. First, the change in volume is calculated, and then the density of the object is calculated by using this formula: density = volume ÷ mass.

Displacement also explains why objects float or sink. Buoyancy is the upward force that a liquid exerts on any object immersed in it. If the mass of the object is greater than the mass of the water that it displaces, the object sinks. If the mass of the object is less than the mass of the water that it displaces, then the object fl oats. This explains how a huge and very heavy ship can fl oat: it displaces a greater mass of water than its own mass.

Other physical properties of substances include conductivity, magnetism and solubility.

The chemical properties of a substance can only be observed during a chemical reaction. They cannot be measured or tested without changing the substance’s composition. For example, the ability to burn easily and combine with oxygen—or fl ammability—is a chemical property of many substances. To observe this, you only have to light a match. The process of burning, or combustion, gives off energy and leaves behind ash. Reactivity is a chemical property that refers to the tendency of matter to undergo chemical reactions. When iron rusts, this silver gray metal known for its strength and magnetic properties combines with oxygen to become iron oxide, which is orange in color and very brittle. So in order to observe the chemical properties of a substance, you must actually change its composition.





a. How does the displacement of water explain whether an object will fl oat or sink?

b. Describe some tests or measurements that you could perform to help identify an unknown substance based on its physical properties.

c. Explain how chemical properties of matter are different from physical properties.

❯ Research

Supplies

❯ 10 popsicle sticks ❯ 10 sheets of paper ❯ 10 magnets ❯ 10 small jars or bottles ❯ 10 pitchers ❯ water

❯ aluminum foil ❯ vegetable oil ❯ baking soda ❯ toothpaste ❯ salt

❯ vinegar ❯ iron fi lings ❯ sugar ❯ cornstarch ❯ sand

Procedure

1 Prepare the substances for testing.

a. Lay out the sheets of paper at 10 stations around the room. b. Beside each sheet of paper, put a magnet, a popsicle stick, a pitcher of water and a jar.c. Put one of the substances for testing (the second and third columns in the supplies list

above) at each station.

2 Work in pairs. Visit each station and do experiments to test the physical properties of the substances.

a. For the solubility test, half-fi ll the jar with water, add a very small amount of the substance, and stir with the popsicle stick to dissolve it. Pour away the mixture after.

b. For the magnetism test, see if the magnet attracts the substance.c. For the density test, half-fi ll the jar with water, add a small amount of the substance, and

see if it fl oats or sinks. Then pour away the water. d. Record all your results in the table on the next page.



Results

1 Record the results in the table.

Substance State Color OdorSolubility in Water

MagnetismDensity

Compared to Water

Salt

Baking soda

Iron fi lings

Aluminum foil

Vinegar

Toothpaste

Sugar

Cornstarch

Vegetable oil

Sand

❯ Analyze

1 Name other substances that are magnetic.

2 Name other substances that are soluble in water.

3 Name other substances that sink in water and other substances that fl oat.

4 Can you think of any other physical properties?



❯ Topic

Key Wordsorganic (adj) – containing carbonvalence electron (n) –an electron in the outer shell of an atom that can participate in the formation of a chemical bond

Objective Distinguish between ionic and covalent compounds

Key Concepts ❯ Ionic compounds form as a result of ionic bonding when a metal atom gives one or more electrons to a nonmetal atom, and both become ions. ❯ Ionic compounds are crystalline solids: they are hard, brittle and strong, and have high melting and boiling points. Many dissolve in water but not in alcohol. ❯ Covalent compounds form as a result of covalent bonding when two nonmetals share their outer shell electrons to attain a more stable state. ❯ Covalent compounds are molecules and can be gases, liquids or solids. They have low melting and boiling points, and many dissolve in alcohol but not in water.

Identifying Substances by Their Physical Properties

8

The many differences in the properties of ionic compounds and covalent, or molecular, compounds result from the nature and strength

of the forces that hold these compounds together. Ionic compounds form when one or more valence electrons transfer from one atom to another, with each atom becoming an ion. The compounds are held together by a strong attraction between these positive and negative ions. Covalent compounds form when atoms of two nonmetals form molecules by sharing a pair of valence electrons. At room temperature, the state of organic covalent compounds—solid, liquid or gas—depends on their molecular weight and the cohesive forces between the molecules: the higher the molecular weight is and the stronger the forces are, the higher the melting

and boiling points. Molecular weight is determined by the size and number of atoms in each molecule, so a compound with many light atoms may have a lower molecular weight than one with a few heavy atoms. Because each molecule of most covalent compounds contains only a few light atoms and the forces between molecules are weak, their melting and boiling points are low.

The attractive forces between positive and negative ions are much stronger than the attractive forces between neutral molecules, which explains their different physical properties, summarized in the table below.

One way to distinguish ionic and covalent compounds is by testing to see if they conduct electricity when dissolved in distilled water. An ionic compound will produce ions that make the water conduct electricity, while a covalent compound will not.

Ionic and Covalent Compounds

Ionic Compounds Covalent Compounds

Examplessodium chloride (table salt), sodium hydroxide (drain cleaner), sodium fl uoride (in toothpastes)

hydrogen chloride (hydrochloric acid), naphthalene (mothballs),sucrose (table sugar)

What They Form ions molecules

Hardness usually hardusually soft (tend to be gases, liquids or soft solids)

Melting Point/Boiling Point

higher melting and boiling points lower melting and boiling points

Conductivitysolids do not conduct electricity; conduct electricity when dissolved in water or when in a liquid state

poor conductors of heat and electricity; do not conduct electricity in water

❯ A molecule of sucrose has 45 atoms.

of ttogonefroatoarebetCovofshatemcomonforthe

Io

❯ A molecule of sucrose has 45 atoms.





a. Explain what happens to metal and nonmetal atoms when an ionic bond forms between them.

b. How does this explain why ionic compounds have a high melting points?

2 A molecule of gasoline contains 10 carbon atoms. A molecule of kerosene contains 16 carbon atoms. Which has a higher boiling point? Explain.

3 A certain covalent compound is solid at room temperature. What can you conclude about its molecular weight?

❯ Research

2 Watch Video 2. Then prepare your supplies.

Supplies

❯ distilled or deionized water ❯ battery-powered fl ashlight with metal case ❯ batteries ❯ insulated electric wire ❯ scissors

❯ electrical tape ❯ aluminum foil ❯ 2 paper clips ❯ 6 plastic cups ❯ teaspoon ❯ table salt

❯ Epsom salt ❯ sugar ❯ cornstarch ❯ vinegar ❯ baking soda ❯ voltmeter (optional)

Procedure

1 Prepare the circuit.

a. Cut two 20-centimeter lengths of wire. Using the scissors, carefully remove about one centimeter of insulation from both ends of each wire.

b. Unscrew the end of the fl ashlight, as if to replace the batteries. Tape the end of one wire to the end of the battery, and tape the end of the other wire to the metal case of the fl ashlight.

c. Turn on the fl ashlight. Test your circuit by touching the free ends of the wires together. This should cause the fl ashlight to light.

d. Cut two strips of foil, long enough to touch the bottom of a plastic cup while folding over the top. Be careful not to touch the end that will be in the water. Use a paper clip to attach the free end of each wire to a foil strip.

e. If you are using a voltmeter instead of a fl ashlight, set it for ohms. Touching the ends of the two probes should cause the needle on the meter to move.



2 Test solutions of compounds for conductivity.

a. Start with a clean plastic cup. Add about three centimeters of distilled water. Put the free ends of the two strips of foil into the water and observe the fl ashlight.

b. Add a teaspoon of table salt to the water and observe the fl ashlight. If the solution conducts electricity, the fl ashlight should light. Record your observations in the table.

c. Repeat the procedure using the other substances. Use a clean cup and fresh foil strips for each substance. Test the distilled water before adding the substances to make sure that it has not been contaminated.

Results

1 Complete the table with the results.

Compound Conductivity in Water Covalent or Ionic

Salt

Epsom salt

Sugar

Cornstarch

Vinegar

Baking soda

❯ Analyze

1 Did the distilled water by itself conduct electricity? Is water covalent or ionic?

2 Which compounds were ionic and which were covalent? Explain.

3 Write other compounds that you think are ionic and covalent.

for each substance. Test the distilled water before adding the substances to make sure that it has not been contaminated.

Results

1 Complete the table with the results.

Compound Conductivity in Water Covalent or Ionic

Salt



❯

1Unit

Progress Check

The Properties of Matter1 Which of these is not a subatomic

particle?

a. An atom.b. A neutron.c. An electron.d. A proton.

2 What is a pure substance made of identical atoms called?

a. A compound.b. An ion.c. An element.d. A proton.

3 How are the elements in the periodic table ordered?

a. By their atomic mass.b. By their atomic number.c. By the number of neutrons.d. By the number of neutrons and

protons.

4 What do elements in each group, or column, have in common?

a. They have the same number of electrons in their outer shell.

b. They have the same number of electrons in total.

c. They have the same number of electron shells.

d. They are all the same kind of element.

5 Which is not a common property of metals?

a. They are gaseous.b. They are ductile.c. They are malleable.d. They are conductive.

6 What does luster refer to?

a. How easily a substance can be beaten into a fl at sheet.

b. How easily a substance can be stretched into wire.

c. How well a substance conducts heat.d. How well a substance refl ects light.

7 Which do not appear in the periodic table?

a. Metals.b. Metalloids.c. Compounds.d. Nonmetals.

8 Which of these is a diatomic molecule?

a. H2.b. HCl.c. NaCl.d. H2O.

9 How does a covalent compound form between two atoms?

a. One atom loses an electron and one atom gains an electron.

b. Both atoms share electrons.c. One atom loses a proton and the

other gains an electron.d. Both atoms share protons and

neutrons.

10 What is an ion?

a. A bond between a metal and a nonmetal.

b. An atom that has lost or gained an electron.

c. An atom that is electrically neutral.d. A valence electron.

11 What is pure water an example of?

a. A solution.b. A solute.c. A solvent.d. An insoluble substance.

12 Which is a chemical property of matter?

a. Color.b. Conductivity.c. Solubility.d. Flammability.

(12 points)



❯ Total: / 32 points

13 Describe how the elements in the periodic table are ordered with reference to the following. (6 points)

a. number of protons:

b. number of electrons in outer shell:

c. number of electron shells:

14 Complete the diagrams to show how the bonds form. (3 points)

a. A covalent bond between hydrogen atoms:

H + H

b. A covalent bond between hydrogen and chlorine:

H + Cl

c. An ionic bond between sodium and chlorine:

Na + Cl

1 5 Draw the electron confi guration of sodium. (2 points)

11Na

Sodium23

16 Describe each type of mixture and give an example. (4 points)

a. A homogeneous mixture:

b. A heterogeneous mixture:

17 Describe how a solar still works. (5 points)17 Describe how a solar still w


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