formation of ion

FORMATION OF ION

An ion is an atom or group of atoms carrying positive or negative charge. Example Ca2+, O2-, SO42- etc.



If a particle has equal numbers of protons (+) and electrons (-), the particle charge is zero, and the particle is said to be neutral.

In a chemical reaction, electron(s) can be transfered from atom to another atom.

If electron(s) is removed from an atom, the number of protons will be more than number of electrons. In this case, the atom will has excess positive charge and hence form a positive ion (cation).

If atom gains negative electrons, there is an excess negative charge in the atom, so a negative ion is formed

Formation of Negative Ion

Example: Formation of Fluoride Ion

A fluorine atom has 9 protons and 9 electrons.

Since the number of protons is equals to the number of electrons, the fluorine atom is neutral.

The electron arrangement of fluorine atom is 2.7. This is not a stable arrangement of electrons.

To achieve the stable electron arrangement of noble gases (octet electron arrangement), fluorine need to receive 1 electron from the other atom

Formation of Positive Ion

Example: Formation of Magnesium Ion

A magnesium atom has 12 protons and 12 electrons and it is neutral.

The electron arrangement of magnesium atom is 2.8.2 .

To achieve the stable electron arrangement of noble gases (octet electron arrangement), magnesium atom need to loss2 electrons

As shown in the diagram above, after losing 2 electrons, the electron arrangement of magnesium become 2.8, which is an octet arrangement of electrons.

At the same time, the number of electrons has reduced by 2 and become 10 electrons while the number of proton remain unchanged.

Hence the charge of the magnesium ion is +2.

The table below shows the difference between a magnesium atom and a magnesium ion in term of its number of proton and electron and its electron arrangement

Ionic Bonding

1. Ionic bonds are formed by one atom transferring electrons to another atom to form ions. Ions are atoms, or groups of atoms, which have lost or gained electrons.

2. The atom losing electrons forms a positive ion (a cation) and is usually a metal. The overall charge on the ion is positive due to excess positive nuclear charge (protons do NOT change in chemical reactions).

3. The atom gaining electrons forms a negative ion (an anion) and is usually a non-metallic element. The overall charge on the ion is negative because of the gain, and therefore excess, of negative electrons.

4. Ions of opposite charge will attract one another, thus creating an ionic bond.

5. The examples below combining a metal from Groups 1 (Alkali Metals), or 2, with a non-metal from Group 6 or Group 7 (The Halogens)