Meet the Elements
Element – a type of pure substance that cannot be
broken down into simpler parts by ordinary chemical
means (examples, gold, oxygen). An element has one kind
of atom.
Compound – a pure substance made up of two or more
elements that are chemically combined (example, water is
a compound consisting of two elements, hydrogen and
oxygen). A compound has two or more kinds of atoms.
Atom – is the smallest unit of matter that can take part
in a chemical change.
Element Symbols – a symbol used to stand for an element
(example, H for hydrogen, Na for sodium).
Chemical Formula – a formula that uses symbols and
numerals to represent the elements in a pure substance.
[example, H2O is the chemical formula for water, H
stands for hydrogen, O stands for oxygen, and the small
number, subscript, stands for the amount of a particular
element in the compound (2 parts of hydrogen for each
oxygen in water)]
Molecule – is the smallest independent unit of a pure
substance and is generally a cluster of atoms bonded
together. The formula H20 tells us that a water molecule
is made of three atoms: two hydrogen atoms and one
oxygen atom.
Table on Page 195
Name of
Compound
Formula of
Molecule
Elements
Present
Water
H2O
Carbon
Dioxide
Propane
CO2
C3H8
Glucose
C6H12O6
Hydrogen,
Oxygen
Carbon,
Oxygen
Carbon,
Hydrogen
Carbon
Hydrogen
Oxygen
How Many
Atoms of
Each?
2 atoms H,
1 atom O
1 atom C
2 atoms O
3 atoms C
8 atoms H
6 atoms C
12 atoms H
6 atoms O
Table on page 196
Name of
Gas
Water
Vapor
Carbon
Dioxide
Oxygen
Nitrogen
Compound Made of
or
Molecules
Element
Compound
Yes
Formula
H20
Number of
Atoms per
Molecule
3
Compound
Yes
CO2
3
Element
Element
Yes
Yes
O2
N2
2
2