CHAPTER 3

Matter – Properties and Changes

Organizing & Describing Matter

Substances – matter that has a uniform and unchanging composition (pure substance) NaCl H2O Salt Water is not a pure substance – depending on

where you take your sample it may have a different composition

Physical Properties of Matter

A physical property is a characteristic that can be observed or measured without changing the sample’s composition

Shape TasteColor HardnessWeight Melting PointDensity Boiling PointOdor

• Pure substances will have uniform physical properties regardless of where the sample comes from – some (not all) of these properties can be used as identifying characteristics

Physical Properties of Matter

Extensive Properties Properties dependent upon the amount of the

substance present Length, volume & mass are dependent upon the

sample observed

Intensive Properties Properties that are independent of the amount of the

substance present Density does not change – it is the same for all samples

of a pure substance Can be used to identify samples of pure substances

Chemical Properties of Matter

Chemical properties are based on the ability of a substance to combine with or change into one or more other substances May involve adding thermal or electrical energy May involve combining substances

Example: iron forms rust when combined with air The inability of a substance to change is a chemical

property Example: iron will not react with Nitrogen gas at room

temperature

Observing Properties of Matter

Properties may change depending on the conditions in which you observe the sample

Physical & Chemical Properties depend on the temperature and pressure Water is liquid at room temperature, gas above 100 oC,

and solid below 0oC When atmospheric pressure increases, the boiling point of

water becomes higher (hotter) When atmospheric pressure decreases (as with increasing

elevation) the boiling point becomes lower (cooler)

We use the statement at standard temperature and pressure (o Kelvin and 1 atm)

States of Matter

Solid – definite shape and volumeLiquid – definite (or constant) volume &

takes the shape of its container (no definite shape); flows

Gas – flows to conform to the shape of its container; fills the entire volume of its container

SolidGas

Liquid

Mixtures

A mixture is a combination of two or more pure substances in which each pure substance maintains its individual chemical properties Anything mixed with water (ie salt water) is a mixture Aqueous solution

Types of Mixtures

Homogeneous Constant composition throughout Always has a single phase Salt water SOLUTIONS

Heterogeneous Does not blend smoothly throughout Parts remain distinct Sand & water

Types of Solution Examples

Changes in Matter

Physical Changes Changes that alter the

substance without changing its composition

Examples ∆ in State of matter

(changes depend on temperature and pressure)

Bend Tear Grind Crumple Split Crush

Chemical Changes Process that involves

one or more substances changing into new substances

New substances are formed with new compositions and different properties than the reactants

Starting substances are called reactants

Ending substances are called products

Examples – rust, explode, oxidize, corrode, tarnish, ferment, burn, rot

Indicators of Chemical Changes

Formation of a gas (bubbles)Formation of a solid (precipitate)

Generally, color changesEnergy given off (heat, light, sound)

Change in Odor

Conservation of Mass

Mass is neither created nor destroyed during a chemical reaction – it is conserved

Massreactants = Massproducts

Elements

Pure substances that cannot be separated into simpler substances by physical or chemical means

91 elements occur naturally on EarthUnique Chemical Name & Symbol

(made of one, two or three letters & first letter is always capitalized

Organized into the Periodic Table

Compounds

Combination of two or more different elements that are combined chemically

Water, table salt, sugar, aspirinCan be broken down into simpler substances by chemical meansTypically involves energy

Law of Definite Proportions

Elements that combine to form compounds in definite proportions

Regardless of the amount, a compound is always composed of the same elements in the same proportion by mass

Percent by mass = mass of the element x 100

mass of compound

Law of Multiple Proportions

When different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers

Understanding Matter