Elements
All
chemical substances are made from atoms. There are just over 90
different kinds of atoms in nature. If a substance is made from just one
kind of atom, we call it an element.
We can represent the names of elements with chemical symbols. Some of
the symbols are the first letter(s) of the element's name. For example:
Carbon
C
Oxygen
O
Nitrogen
N
Calcium
Ca
Helium
He
Some
of the symbols come from the old name of the element. For example:
Copper
Cu from cuprum
Sodium
Na from natrium
Atoms
are composed of three sub-atomic particles that are arranged as shown
below.
|
electrons
orbiting |
 |
protons
and neutrons in the nucleus |
The nucleus
of an atom is made up of protons and neutrons. Electrons orbit the nucleus
in orbits or shells. The protons have a positive charge, the electrons
have a negative charge and the neutrons are neutral (are not charged).
The
atoms of each element have different numbers of protons.The number of
protons contained in the nucleus of an atom is called the atomic number.
The elements are arranged in the periodic table in order
of their atomic number.
The
rows of the periodic table are called periods and tells us how
many electron shells the atom has. For example hydrogen is in period 1
(row 1) and has one electron shell, potassium is in period 4 (row 1) and
has four electron shells.
The
columns of the periodic table are called groups. The elements in
each group have the same number of electrons in their outermost shell.
For example the elements in group II have two electrons in their outermost
shell. The elements in each group also have similar chemical properties.
Some
elements are metals, some are non-metals and some have properties of both
metals and non-metals and are called metalloids.
On
a copy of a periodic table mark the group numbers and the period numbers.Using
different colours, shade in the metals, the non-metals and the metalloids.
