Unit 7: Structureof Matter
l27.0
13
10.8
5
35.5
6
Unit 7: Structure of Matter 113
l27.0
13
10.8
5
35.5
6
Vocabulary
Study the vocabulary words and definitions below.
compound ....................................... a substance formed when two or moreelements combine chemically
element ........................................... a substance that cannot be broken downinto a simpler form by ordinarychemical means
formula ........................................... the way a chemist tells how two or moreelements are combined to make acompoundExample: H2O is the formula for water
hydrogen (H) .................................. the lightest and most abundant of allelements; occurs as a gas when not inother substances
mixtures .......................................... two or more substances put together; nochemical reaction takes place and theyare easily separated
oxygen (O) ...................................... an element found as a gas when not inother substances; it has an atomicnumber of eight and is involved inburning and rusting
symbols ........................................... the letters used by scientists to representthe names of the elements
Unit 7: Structure of Matter 115
l27.0
13
10.8
5
35.5
6
Introduction
You have seen how scientists represent the reactions that createsubstances. You may have wondered how two substances with oxygen inthem (like water and sugar) could be so different. In this unit, we willdiscuss what properties these substances have that make them unique.
Elements
By now we know that matter has mass, volume, and density. We alsoknow that matter can be a solid, liquid, or a gas. We have also learnedsome of the physical and chemical properties of matter. We experimentedto show that chemical changes produce new substances. However, whatmakes up matter? Think about water. Water can be broken down intohydrogen and oxygen. The substances of hydrogen and oxygen cannot bebroken down by chemical means. These substances are called elements.Elements cannot be broken down by chemical action. All substances are
made of elements.
If you look at all the buildings around you,you see that they come in many differentshapes and sizes. But there are similaritiesbetween the buildings. Think of a pyramidand a castle. Both are made of stone blocks,but the blocks have been arranged in verydifferent ways. By doing this, the builders
made the structure they wanted. You can think of elements as buildingblocks. On Earth, we have discovered about 120 elements. While some ofthe elements can only be found in very special labs, these are all theelements that we know exist. Everything is made from these elements.
Some substances are made of only a single element. Aluminum (Al), gold(Au), oxygen (O), and hydrogen (H) are examples of substances with asingle element.
examples of substances with a single element
27.0 197.0 16.0 1.008
8 P8 N
1 atomof oxygen
1 P
1 P
2 atomsof hydrogen
water molecule broken down intoits elements
Unit 7: Structure of Matter116
l27.0
13
10.8
5
35.5
6
Most elements are solid under normal conditions. Few are liquid. Themercury (Hg) used in thermometers is normally liquid.
Many other elements are gases under normal conditions. Oxygen (O) andhydrogen (H) are just two of the elements that are gases at roomtemperature.
Scientists have a special way of writing the names of elements. They useletters instead of writing the whole word. The letters are called symbols.Here are some of the common ones.
Copper
Aluminum
Iron
Mercury
Oxygen
Hydrogen
Silver
Gold
Carbon
Cu
Al
Fe
Hg
O
H
Ag
Au
C
Elements Symbols
Each of the elements has its own symbol. Each element has at least oneproperty that makes it different from another element.
Unit 7: Structure of Matter 117
l27.0
13
10.8
5
35.5
6
Compounds
Many substances are made from more thanone element. Elements can unite with eachother. The elements form new substances thatare very difficult to separate. The newsubstances are called compounds. Acompound has chemical and physicalproperties that are uniquely its own. It maylook totally different from the elements thatformed it. As you have seen, the atoms of twoelements, hydrogen (H) and oxygen (O),combine to form water.
Sugar is a compound formed by atoms of carbon (C), hydrogen (H), andoxygen (O).
carbon
sugar(a compound)
hydrogen
oxygen
C6
O6
C6
O6
H12H
12
Sugar and water do not look like the elements that formed them. Whencompounds are formed, the elements always combine in the sameproportions. A formula tells how elements combine to form compounds.The formula for water is H2O. Compounds always have formulas.
Mixtures
It is possible to combine two elements or compounds without producingnew substances. No chemical change takes place. These substances arecalled mixtures. Mixtures can be separated. Each substance in the mixturekeeps its own properties. If you mix iron filings with sand, you couldseparate them because there has been no chemical reaction. There is nonew compound; there is only iron and sand.
8 P8 N
1 P
oxygen
1 P
hydrogenhydrogen
Water Molecule
Unit 7: Structure of Matter118
l27.0
13
10.8
5
35.5
6
If we took hydrogen and combusted it with oxygen, water would beformed. Water does not have the same properties as hydrogen and oxygenbecause it is a different compound. Water is always made from twohydrogen atoms and one oxygen atom. Water cannot be made any otherway because it is not a mixture.
On the other hand, a mixture can be made in many different ways. Air is amixture. The elements in the air are not always the same. Tossed salad is amixture too; salads do not always have the same ingredients. Mixtures donot have formulas. They are not formed by chemical changes.
A tossed salad is a mixture too; salads do not alwayshave the same ingredients.
Summary
Now we know that elements are the simplest forms of substance. Gold(Au) is an element. Compounds are formed when a chemical change takesplace between two or more elements. Mixtures are formed when two ormore substances are put together. No chemical change takes place. Theparts of a mixture can easily be separated.
Unit 7: Structure of Matter 119
l27.0
13
10.8
5
35.5
6
Practice
Use the periodic table of the elements on pages 98-99 to identify each of theelements whose symbols appear below. Write the name and the atomic numberfor each element on the line provided.
1. C
2. Au
3. Ag
4. Hg
5. Cu
6. Fe
7. H
8. O
9. Al
element's name &atomic number
Unit 7: Structure of Matter120
l27.0
13
10.8
5
35.5
6
Lab Activity: Part 1
Investigate:• You will differentiate between a compound
and a mixture and separate the substances in a mixture using physical means.
Facts:• The substances in mixtures do not combine
chemically.
Materials:• sulfur• paper• iron filings• ring stand and clamp
• Bunsen burner• magnets• test tube
Part 1
1. Pour some sulfur onto a sheet of paper.
2. Add some iron filings. Mix the sulfur and the iron filings together.
a. Did a chemical change take place? ________________________
b. Are any new substances formed? _________________________
c. Did the iron and the sulfur keep their own properties? ______
3. Move a magnet near the sulfur and the iron filings.
a. Can you separate the iron from the sulfur? _________________
b. Did the iron and the sulfur form a mixture or a compound?
________________________________________________________
Unit 7: Structure of Matter 121
l27.0
13
10.8
5
35.5
6
Lab Activity: Part 2
1. Mix the iron filings and the sulfur on a sheet of paper.
2. Pour the mixture into a test tube.
3. Place the tube in clamp on a ring stand.
4. Heat the tube until it begins to glow.
5. Let the test tube cool.
6. Remove the substance from the test tube.
a. Can you see the iron? ___________________________________
b. Can you see the sulfur? __________________________________
c. Could you separate the iron from the sulfur using a magnet?
______________________________________________________
d. Did you make a new substance? __________________________
e. Is this new substance a mixture or a compound? ____________
Note: This new substance is called Iron Sulfide.
f. What are the two elements that formed the substance?
______________________________________________________
Unit 7: Structure of Matter122
l27.0
13
10.8
5
35.5
6
Practice
Use the list below to complete the following statements. One or more terms will beused more than once.
120 copper hydrogen oxygenaluminum element laboratories silvercarbon elements liquidchemical gold mercury
1. An is a substance that cannot be broken
down into a simpler form and from which other substances may be
made.
2. There are about different kinds of
elements.
3. All substances are made from .
4. is an example of a solid element.
5. Mercury is an element that is normally in a
form or state.
6. changes produce new substances.
7. Some elements are only found in .
8. Au is the symbol for .
9. Cu is the symbol for .
10. C is the symbol for .
Unit 7: Structure of Matter 123
l27.0
13
10.8
5
35.5
6
11. Al is the symbol for .
12. Ag is the symbol for .
13. O is the symbol for .
14. H is the symbol for .
15. Hg is the symbol for .
Unit 7: Structure of Matter124
l27.0
13
10.8
5
35.5
6
Practice
Write True if the statement is correct. Write False if the statement is not correct.
__________ 1. Two or more elements combine chemically to form asubstance.
__________ 2. Sugar is a mixture, not an element.
__________ 3. Compounds are very easy to separate.
__________ 4. Hydrogen and oxygen combine to form water.
__________ 5. Compounds have the same properties as the elementsfrom which they are formed.
__________ 6. A compound is formed when two or more substancesare put together and no chemical change takes place.
__________ 7. All mixtures have formulas.
__________ 8. Mixtures can easily be separated.
__________ 9. Oxygen is a compound.
_________ 10. Air is a mixture.