Classifying Matter According to its Composition

MixturesElements & Compounds

• Mixtures - Another way to describe matter

• Other ways:– Physical state– Chemical and physical properties– Density

Matter

Pure substance Mixture

Element Compound Homogeneous Heterogeneous

Which can exist as

Composition of Matter

Pure Substance = sample of matter with only one component

• Elements = pure substances that cannot be broken down into simper substances with different properties

• Compounds = a pure substance made up of two or more elements that are chemically combined in a fixed proportion by mass

Mixtures

= a combination of two or more substances in which each retains its own identity

- May be a homogenous mixture

OR

- May be a heterogeneous mixture

Mixtures• Homogeneous mixtures -

– A mixture of two or more components that is uniform throughout.

– Every portion of the sample is identical

- Components cannot be separated out or will not settle out

- Can exist as a solid, liquid or gas

– For example • brass (a mixture of zinc & copper.)• Salt water (Sodium chloride dissolved in water)

• air (a uniform mixture of N2, O2, CO2 and trace gases)

Mixtures

• Heterogeneous mixtures

– have 2 or more components

- components have distinct regions with definite boundaries

- can be separated by some physical property

- can exist as liquids or solidsFor example:

• Soil – bits of sand, black soil, organic matter

• Blood - appears homogeneous but it is actually a heterogeneous mixture of red and white blood cells that are visible under a microscope.

http://www.chem.ufl.edu/~chm2040/cgi-bin/image_eval.cgi?Op=display&Chapter=1&File=substances&Image=c2f19.gif

In-between Classification

• Colloid or colloidal dispersion - mixture that is not quite heterogeneous and not quite homogeneous

• Example – milk is a colloid. The particles are too small to be seen unaided but are small enough that they will not settle out

• Others = fog, smoke, whipped cream, mayonnaise, marshmallows

Another type of Mixture

• Suspension – where particles are large enough that they will eventually settle out

• mixture in which the particles of one substance are scattered in another without dissolving

• Example – making a clay pot. The clay particles in the mixture eventually settle out.

Suspension - the particles which are temporarily suspended in the liquid are large enough to collectively make the material appear cloudy. - They will settle out after a while. You can now see that after several minutes, the particles in the suspension have settled to the bottom.

Differentiating between mixtures

Differentiating between mixtures

Colloidal dispersion - very small particles spread throughout the liquid which are large enough to reflect light, but not large enough to be seen individually. -may look either clear or cloudy in ordinary room light. -particles in remain dispersed in the liquid and will not settle out.

Differentiating between mixtures

A solution, on the other hand, will appear clear even when a light is shown through it.

Classifying Matter as Elements or Compounds

• Pure substances: is matter that has distinct properties and a composition that doesn’t vary from sample to sample. It only has one component. It’s either an:– Element: a substance that cannot be broken down

any further into simpler substances with different properties.

– Compound: a substance that is composed of two or more elements that are chemically combined in a fixed proportion by mass.

Classifying Matter• Elements:

– Simplest from of matter– Presently 114 known elements– 90 of them are naturally occurring, rest are man-

made– Every element has its own unique set of physical

and chemical properties– Each element has its own name and symbol

• Name is always in English• Symbol will be one capitol letter or a capitol letter

followed by a single un-capitalized letter.

Elements on the Periodic Table

• What is the periodic table?

-a chart that shows all of the known elements

-give information about each element

Why Know About the Periodic Table??

• The periodic table is the most important chemistry reference there is. 

• It arranges all the known elements in an informative array.

• Its main use is to predict the chemical properties of an element based on where it is located on the table.

• People familiar with how the table is put together can quickly determine a significant amount of information about an element.

Some Common Elements & Their SymbolsCarbon C Aluminum Al Copper Cu (cuprum)

Fluorine F Barium Ba Iron Fe (ferrum)

Hydrogen H Calcium Ca Lead Pb (plumbum)

Iodine I Chlorine Cl Mercury Hg (hydragyrum)

Nitrogen N Helium He Potassium K (kalium)

Oxygen O Magnesium Mg Silver Ag (argentium)

Sulfur S Silicon Si Tin Sn (stannum)

Think Inside the BoxWhen you look at the

periodic table, you should notice that each box represents a different element, and each box contains vital information about the element, – Name

– symbol

– atomic number

– atomic mass

6

C

Carbon

12.011

• The top number is the atomic number.

• Every element has its own unique atomic number.

• The atomic number tells how many protons are in one atom of that element.

• Since no two elements have the same atomic number, no two elements have the same number of protons.

6C

Carbon

12.011

• The large letter is the element's symbol

• Just below that is the element's name.

• Each element has its own unique symbol and name.

6C

Carbon

12.011

• Below the name is the element's atomic mass.

• The atomic mass is the sum of the protons and neutrons in the nucleus

• The atomic mass essentially gives you an estimate of how massive one atom of that element is

6C

Carbon

12.011

• The vertical columns of the periodic table (there are 18) are called groups or families.

• The elements in a group have the same number of electrons in their outer shell.

• As you keep counting the columns and you'll know how many electrons are in the outer shell.

• All of the elements in a period have the same number of atomic SHELLS

• Both elements in the top row (the first period) have one shell for their electrons. All of the elements in the second period have two electron shells. The number of shells increases as you go down the table.

• Atoms on the left of the period are usually larger and more lightweight than the smaller, heavier atoms on the right of the period.

• Electrons of atoms with similar energy are grouped in an energy level called a shell.

• The shells closest to the nucleus contain electrons with the lowest energies, whereas shells farther away from the nucleus contain electrons with higher energies

Electron Shells

3 Main Categories of Elements

• Metals

• Non-Metals

• Metalloids

3 Main Categories of Elements

Metals

• On the left side of the table• All are solid except for mercury• Described as shiny, ductile (most metals

can be drawn out into thin wires), malleable (most metals can be hammered into thin sheets )

• All are good conductors of electricity• All are good conductors of heat

Non-metals

• On the right side of the periodic table

• Some are solid, some are gases.

• Bromine is a liquid

• Under most conditions are not good conductors of heat or electricity

Metalloids (semi-metals)

• Elements along the stair-step line

• These elements display the properties of metals and non-metals, depending upon the conditions.

Forming Compounds

• Compounds are pure substances made up of 2 or more different elements in a different proportion.

• Electrons are primarily involved in the combination of atoms to form compounds.

Composition of Compounds

• Each is put together so that every unit of that compound is identical to every other unit

• They are different from every other compound

Examples of Compounds

• Water - made up of hydrogen and oxygen

• Carbon dioxide – made up of carbon and oxygen

• Rust – made up of iron and oxygen

• Sugar – Made up of carbon, hydrogen and oxygen

Naming Compounds

• Chemical formula – describes exactly what elements and the number of atoms of each element occurs in the smallest particle of that compound.

• We identify what elements are present by their symbol

• How many of those elements present are indicated by the subscript following the symbol.

Chemical Formulas

• Water = H20

means that each unit of water contains 2 atoms of hydrogen and one atom of oxygen

• Sugar (sucrose)= C12H22011

How many atoms of each element are in sugar?

Matter

Pure substance Mixture

Element Compound Homogeneous Heterogeneous

•Sodium•Chlorine•Hydrogen

•Salt•Water•Sugar

•Atmosphere•Salt in water•Black Coffee

•Oil & water•Salt & Pepper•Sugar & sand

MoleculesAtomsMake up

Which can exist as

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