THE COMPONENTS OF MATTER
Refer to the definitions of an element and a compound.
Unlike compounds, elements cannot be broken down by chemical changes into simpler materials.
contain different types of atoms; there is only one type of atom in an element.
1) A compound has constant composition but a mixture has variable composition. 2) A compound has distinctly
different properties than its component elements; the components in a mixture retain their individual properties.
a) The fixed mass ratio means it has constant composition, thus, it is a
b) All the atoms are identical, thus, it is a
c) The composition can vary, thus, this is an
d) The specific arrangement of different atoms means it has constant composition, thus, it is a
Review the definitions of elements, compounds and mixtures.
a) The presence of more than one element makes this pure substance a
b) There are only atoms from one element so this pure substance in an
c) The presence of more than one compound makes this a
d) The presence of more than one type of atom means it cannot be an element. The specific, not variable,
arrangement means it is a
Some elements, such as the Noble gases (He, Ne, Ar, etc.) occur as individual atoms. Many other elements, such
as most other nonmetals (O
, etc.) occur as molecules.
Compounds contain atoms from two or more elements, thus the smallest unit must contain at least a pair of atoms.
Mixtures have variable composition; therefore, the amounts may vary. Compounds, as pure substances, have
constant composition, thus their composition cannot vary.
The tap water must be a mixture, since it consists of some unknown (and almost certainly variable) amount of
dissolved material in solution in water.
This is a mixture. No, the constant mass ratio of the components indicates mixtures that have the same
composition by accident, not of necessity.
If you have no reliable way of determining the composition of a sample, you have no hope of knowing if its
composition is constant.
Restate the three laws in your own words.
a) The law of mass conservation applies to all substances —
elements, compounds and mixtures
can neither be created nor destroyed, whether it is an element, compound, or mixture.
b) The law of definite composition applies to
only, because it refers to a constant, or definite,
composition of elements within a compound.
c) The law of multiple proportions applies to
only, because it refers to the combination of elements to
In ordinary chemical reactions (i.e., those that do not involve nuclear transformations), mass is conserved and the
Law of Conservation of Mass is still valid.