Unit 1 – Chapter 3 Notes Mr Nelson

The Properties of Matter Matter: The “stuff” that makes up the universe Has mass and volume All matter is made up of tiny particles called atoms

Elements and Compounds There are over 100 different kinds of atoms We call these different types of atoms different elements All matter is made up of different combinations of elements

Molecules A molecule is made of atoms that are “stuck” together Smallest part of a compound that has properties of that compound Can be the same atoms

Compounds Compounds: substances made by bonding atoms together in specific ways. Two or more different types of atoms bonded together A compound has the same particles throughout

Pure Substances Pure substances always have a definite composition Elements Specific Compounds They are not generic (Orange Juice)

Physical vs. Chemical Properties Chemical Properties: examples are: Rusting, not reacting, fermentation, combustion You must perform a chemical reaction to test chemical properties (and then you change the substance!)

Physical vs. Chemical Properties Physical properties: examples are: Odor, color, volume, solid, liquid, or gas, density, melting point, boiling point You can test physical properties without changing the substance

Intensive vs Extensive Properties Depend on how much substance Mass, length, volume Intensive Inherent quality of substance Density, odor, color

Chemical and physical changes Physical changes – don’t affect the composition of the substance Involves physical properties Solid  liquid  gas Chemical changes – a given substance is changed to another substance Silver tarnishing Leaves growing from soil, water, and air

Which is which? Iron is melted Iron combines with oxygen to form rust Wood burns in air A rock is broken in to small pieces Milk turns sour Wax is melted Wax catches on fire A bee stings you and you swell up

Mixtures and Pure Substances A mixture is something that has variable composition Wood – varies depending on the tree it is cut from Soda – contains lots of dissolved substances (CO2, sugar) Air – contains lots of different substances in different amounts, depending on where you are.

Substances in the air N2 = 78.08% O2 = 20.95% H2O = depends on humidity Ar = 0.93% CO2 = 0.033% Ne = 0.0018% He = 0.00052%

Compounds vs. Mixtures The air is not the same everywhere Florida’s air is probably not the same as Death Valley’s air!

Gold Pure gold is too soft and “bendy” (the scientific word is malleable) to be useful We mix it with silver and copper to strengthen it Mixtures of metals are called Alloys

Compounds vs. mixtures Remember – a compound has particles that are ALL THE SAME A mixture has different compounds/elements in different proportions Is this an example of a mixture or a compound?

Pure substances A pure substance always has the same composition Pure substances can be elements or compounds Mixtures can be separated in to pure substances: Two or more pure substances Mixtures

Types of mixtures Homogeneous mixtures: the mixture is the same throughout Gatorade Salt water These are also called solutions Heterogeneous mixtures: some regions have different properties than others (not uniformly mixed) Sand in water Dirt

Which is which? Gasoline A stream with gravel at the bottom Maple syrup Oxygen and helium in a scuba tank Air Brass Copper metal Sodium chloride (salt)

Law of Definite Proportions Compounds are always composed of the same elements. Table salt is always sodium chloride, otherwise it is something else Example: A 58.5 gram sample of Table Salt is composed of 23.0g of Sodium. What mass % is sodium & chlorine?

Law of Multiple Proportions When different compounds are formed by the combination of the same elements the mass ratio of the two elements of the different compounds is a whole number. Hydrogen and Oxygen – 2 compounds H2O H2O2

Mass % of element in one compound compared to % mass of same element in a different compound is always a whole number ratio.

Law of Multiple Proportions Example: Iron combines with oxygen in different ratios FeO & Fe2O3 In a 100g sample of each In compound 1 Fe is 77.7g of the compound In compound 2 Fe is 69.9g of the compound Find the whole number ratio of the mass %’s? Which compound is which? (Hint: definite prop)