3. Solid
–Highest density of the 3 phases (usually; water
is an exception)
–Very little particle motion
–Particles close and maintain relative positions
–Strong attraction between particles
–Not compressible
–Maintains own shape and volume
Gas
Liquid
Solid
Shape
indefinite
indefinite
definite
Volume
indefinite
definite
definite
Classification of Matter
Pure Substances and Mixtures
A. Pure substances – have distinct properties and
constant composition
1.Elements
2.Compounds
Elements
•Simplest known substances
•One type of atom present - singly or in chemically
bonded groups (molecules)
•Cannot be decomposed to other substances
•About 116 elements known
•All other substances made from combinations of
elements
•Chemical symbols
•One or two letters
•First letter capitalized
•Second letter lower case
•Examples: H, C, N, Li, Co, He, Be
You MUST use STANDARD PRINTED letters for
chemical symbols. Start learning the first 20.
Compounds
•Chemical combination of 2 or more elements
•Atoms arranged in molecules (covalent) or
arrays (ionic) (will discuss later)
•The proportions (ratios) of elements in
compounds are the same irrespective of how the
compound was formed.
-Law of Constant Composition (or Law of
Definite Proportions):
–The composition of a pure compound is
always
the same.
•Symbols called the chemical formula
•Display symbols of elements present
•Subscripts tell relative ratios
•Subscripts refer to element that precedes it
•H2O
two atoms of hydrogen for every one
atom of oxygen
B. Mixtures consist of 2 or more pure substances
- have variable properties and composition
(different proportional mixtures can be made)
1. Homogenous mixtures – solutions; look
uniform throughout
(examples: salt water, air, alloys)
2. Heterogenous mixtures – nonuniform
appearance,
distinct phases visible
(examples: asphalt, sand and salt)
See figure 1.4 in the text.
Physical and Chemical Properties and Changes
•Physical properties – observable without changing
what substance is present
–Color, density, mass, boiling point, shape, etc.
•Physical changes –changes that do not change the
substance(s) present
–Phase changes (melting, boiling, etc.)
–Movement of particles
•Chemical properties – observable when a
chemical reaction takes place and substance(s)
present change
–Flammability, reactivity with metals, etc.
•Chemical changes –changes that DO change the
substance(s) present (reactions)
–Gasoline burns to make carbon dioxide and water
Purification of samples
Mixtures-components of a mixture are separable
by physical methods
-End up with pure substances
Examples:
distillation (liquid to gas change)
filtration (uses particle size and movement)
Separation of Mixtures
• Chromatography
– Mixture exposed to 2 things
• Stationary phase (doesn’t move)
• Mobile phase (moves across the stationary
phase)
• Components separated by unique attraction
to each of the 2 phases
– Example: paper chromatography
Separation of Elements from Compounds
Compounds
-elements in a compound are separable by chemical
methods (reactions)
-End up with elements
Example: electrolysis of water