Pure SubstancesMixtures

Everything that has mass and volume is called matter.

• Fixed composition

• Cannot be separated into simpler substances by physical methods (physical changes)

• Can only be changed in identity and properties by chemical methods

• Properties do not vary

Compounds

• Can be decomposed into simpler substances by chemical changes, always in a definite ratio

Elements

• Cannot be decomposed into simpler substances by chemical changes

• Variable composition• Components retain their characteristic

properties• May be separated into pure substances by

physical methods• Mixtures of different compositions may have

widely different properties

Homogenous mixtures look the same throughout but can be separated by physical means (dissolution, centrifuge, chromatography, osmosis etc.).

Examples: milk, yogurt

• Have the same composition throughout• Components are indistinguishable

Examples: alloys, milk, pop, air.

Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).

• Do not have same composition throughout

• Components are distinguishable

Examples: fruit salad, vegetable soup, etc.

Classification of MatterSolutions are homogeneous mixtures

LiquidsMaterial Density (gm cm-3)

Water at 4 C 1.0000Water at 20 C 0.998

Gasoline 0.70Mercury 13.6

Milk 1.03Solids

Material Density (gm cm-3) Magnesium 1.7Aluminum 2.7

Copper 8.3-9.0Gold 19.3Iron 7.8Lead 11.3

Platinum 21.4Uranium 18.7Osmium 22.5Ice at 0 C 0.92

Gases at STP Material Density (gm cm-3)

Air 0.001293Carbon dioxide 0.001977

Carbon monoxide 0.00125Hydrogen 0.00009

Helium 0.000178Nitrogen 0.001251