Chemistry Reference
In-Depth Information
Atoms - the smallest particles
Everything is made up of billions of atoms. The
atoms of all elements are extremely small; in
fact they are too small to be seen. The smallest
atom known is hydrogen, with each atom being
represented as a sphere having a diameter of
0.000 000 07 mm (or 7 × 10
−8
mm) (Table 2.3).
Atoms of different elements have different diameters
as well as different masses. How many atoms of
hydrogen would have to be placed side by side
along the edge of your ruler to fill just one of the
1 mm divisions?
a
A premature baby needs oxygen.
Table 2.3
Sizes of atoms.
Atom
Diameter of atom/mm
7
×
10
−8
Hydrogen
12
×
10
−8
Oxygen
20.8
×
10
−8
Sulfur
Chemists use shorthand symbols to label the
elements and their atoms. The symbol consists of
one, two or three letters, the first of which must be a
capital. Where several elements have the same initial
letter, a second letter of the name or subsequent
letter is added. For example,
C
is used for
carbon
,
Ca
for
calcium
and
Cl
for
chlorine
. Some symbols
seem to have no relationship to the name of the
element, for example
Na
for
sodium
and
Pb
for
lead
. These symbols come from their Latin names,
natrium for sodium and plumbum for lead. A list of
some common elements and their symbols is given in
Table 2.4.
b
Artists often use charcoal (carbon) to produce an initial sketch.
Molecules
The atoms of some elements are joined together in
small groups. These small groups of atoms are called
molecules
. For example, the atoms of the elements
hydrogen, oxygen, nitrogen, fluorine, chlorine,
bromine and iodine are each joined in pairs and they
are known as
diatomic
molecules. In the case of
phosphorus and sulfur the atoms are joined in larger
numbers, four and eight respectively (P
4
, S
8
). In
chemical shorthand the molecule of chlorine shown
in Figure 2.5 is written as Cl
2
.
c
Neon is used in advertising signs
Figure 2.4
Some non-metals.
