|
|
|
 |
|
|
|
|
|
Home
| About Atoms | The
Periodic Table |
|
|
|
|
|
|
|
 |
|
|
  |
|
|
|
|
|
|
|
 |
|
|
|
|
| There are more than a hundred different elements in
the universe. And, of course, arranging them in some kind
of order would help! They could be arranged in alphabetical
order but that wouldn't tell you much about their chemistry.
In the periodic table, the elements are arranged according
to their atomic number. |
| Notice how the atomic number (top left hand corner)
increases as you move across the table. Normally, the
higher the atomic number, the heavier the element. So
lead (Pb), atomic number 82 is heavier than tin (Sn) atomic
number 50. Examine the periodic table and find out which
is heavier gold (Au) or silver (Ag)? |
|
|
 |
|
|
 |
|
|
| The behaviour of different elements changes periodically
as their atomic number increases. In other words, if you
know the atomic number of an element, then you can predict
how it's likely to behave, in the same way that you can
predict the behaviour of the Moon. The shape of the moon
(as seen from earth) changes periodically, according to
the day. In other words, if we know what day it is, we
can predict the shape of the moon. Every 28th day, there
is a full moon. |
| Now try reading the periodic table up and down, not
left to right... |
| The elements are arranged in columns, or groups, so
that the periodic behaviour of the elements can be seen
at a glance. Each group of elements behaves in
a similar fashion. |
| Take Group One, for example. All the elements in group
one (on the far left hand side) are metals. They are all
highly reactive and they all form alkali solutions in
water. This is why they are sometimes called the alkali
metals. Sodium (Na) is the most common Group One metal.
|
| The Russian scientist, Dmitri Mendeleev, who compiled
the first periodic table, left spaces for elements which
he thought ought to exist but which had not yet been discovered.
And, sure enough, just over a hundred years after Mendeleev
designed his periodic table, all these spaces have been
filled! |
|
|
|
|
|
|
|
|
|
|
