Classification of Matter

Question 1

Pure Substances

Answer 1

Pure substances – (elements and compounds) cannot be separated into other kinds of matter by physical
processes (e.g. boiling, filtration, etc).

Question 2

Elements

Answer 2

cannot be decomposed into stable simpler substances by ordinary chemical means.
(Note: elements can be converted into other elements during a nuclear reaction but we don’t consider nuclear
reactions to be “ordinary chemical means”.)

 Elements are composed of discrete particles called atoms (details covered later in this course).

 Each element has its own box on the periodic table and is represented by one or two letters (symbols).
Upper case letters are used to represent elements. If the symbol for an element contains two letters, then
the second letter must be lower case.

Ex: Co (one uppercase letter) is the element Cobalt, while CO (two uppercase letters) is the
compound carbon monoxide which contains the elements Carbon atom and an Oxygen atom.

Question 3

Atomic Elements

Answer 3

are individual atoms, such as Ne(g), or continuous sets of atoms found together in the bulk
such as most pure metals.

Question 4

Molecular Elements

Answer 4

are discrete units with a small number of atoms arranged in a particular way, such as
hydrogen gas = H2(g).

Question 5

Allotropes –

Answer 5

are different forms of the same element.

Ex: O2 (molecular oxygen) and O3 (ozone) is two allotropes of the element oxygen. Note: both O2 and O3 are
classified as elements (molecular elements) because they contain only one kind of element. They are NOT
compounds.

Ex: Graphite and diamond are two of the many allotropes of carbon.

Question 6

Compound

Answer 6

a substance that is composed of two or more different elements.

• A compound can be decomposed into its elements by chemical means.

Ex: NaCl (sodium chloride = table salt) is a compound because it is made of two different elements (sodium, Na
and chlorine, Cl).

Question 7

Mixtures

Answer 7

consist of two or more substances that do not lose their individual identities. Components of a
mixture are present in variable amounts and can be separated by physical means (boiling, filtration, etc.).

Question 8

Homogeneous Mixtures

Answer 8

have a uniform composition throughout the sample. Analyzing any part or quantity
of the sample would yield the same percentage of each component.

Ex: Sugar dissolved in water.
Ex: The air we breathe near sea level on Earth (78% N2, 21% O2, 1% other gases).

Question 9

Heterogeneous Mixtures

Answer 9

do not have a uniform composition throughout the sample. Contain distinct phases
of homogeneity matter.

Ex: Sand and water.
Ex: Oil and water.