Chemistry Reference
In-Depth Information
THE CHEMICAL
ELEMENTS
APPENDIX I
The chemical
elements
are substances that cannot be decomposed into
simpler substances by chemical means, but combine with other elements to
form new substances. All
substances
and
materials
other than the elements are
made up from the combination of two or more elements. Thus, either singly
or in combination with others, the elements constitute all matter. Well over
100 elements occur in nature, but only 92, listed below, occur in the planet
earth.
The smallest unit having the chemical properties of the element are the
atoms
. All atoms are made up from a number of
elementary particles
known
as the
protons
,
neutrons
, and
electrons
. The
protons
and
neutrons
make up an
atomic nucleus
at the center of the atom, while the
electrons
, distributed in
elec-
tron shells
, surround the atomic nucleus. The atoms of each element are iden-
tical to each other but differ from those of other elements in
atomic number
(the number of protons in the atomic nucleus) and
atomic weight
(their
weighted average mass) as listed in the table below.
Atomic
Atomic
number
Symbol
Name
Weight
number
Symbol
Name
Weight
1
H
Hydrogen
1.0
12
Mg
Magnesium
24.3
2
He
Helium
4.0
13
Al
Aluminum
26.9
3
Li
Lithium
6.9
14
Si
Silicon
28.1
4
Be
Beryllium
9.0
15
P
Phosphorus
30.9
5
B
Boron
10.8
16
S
Sulfur
32.1
6
C
Carbon
12.0
17
Cl
Chlorine
35.5
7
N
Nitrogen
14.0
18
Ar
Argon
39.9
8
O
Oxygen
16.0
19
K
Potassium
39.1
9
F
Fluorine
19.0
20
Ca
Calcium
40.1
10
Ne
Neon
20.2
21
Sc
Scandium
44.9
11
Na
Sodium
23.0
22
Ti
Titanium
47.9
