Formulae of Ions Part 1 - First Twenty Elements

How do we find decide the ionic charges of the various ions? For O level examinations, you are expected to know how to derive the ionic charges for certain elements.

Technique.
Lets select an element, e.g. Magnesium.
Magnesium has the following information based on the periodic table.
Number of protons: 12
Number of neutrons: 12
Number of electrons: 12

The electronic configuration of magnesium is 2,8,2.
The next thing is to ask yourself, in order to obtain a stable electronic configuration (full outer electron shell), the atom needs to do something.
a) Lose 2 electrons so that the configuration becomes 2,8 (full outer electron shell)
b) Gain 6 electrons so that the configuration becomes 2,8,8 (full outer electron shell again)

From all the atoms' point of view, it is easier to lose 2 electrons than to gain 6. So in order to form a stable electronic configuration, magnesium will choose to lose 2 electrons and the updated sub atomic particles looks like this.
Number of protons: 12
Number of neutrons: 12
Number of electrons: 10
Since electrons are negatively charged and protons are positively charged, there will be a total of 12 positive charges and 10 negative charges and hence the overall charge is +2.
Therefore the charge on magnesium is +2

Lets take another example, oxygen.
Subatomic particles of oxygen atom looks like this
Number of protons: 8
Number of neutrons: 8
Number of electrons: 8
Electronic configuration: 2,6
In order to be stable oxygen needs to gain 2 electrons (instead of losing 6 electrons) to form a stable electronic configuration.

After gaining 2 electrons, the new numbner of subatomic particles looks like this.
Number of protons: 8
Number of neutrons: 8
Number of electrons: 10
In this ion, there are 8 positive charges and 10 negative charges, hence it has an overall charge of -2. Therefore the ion of oxygen has a charge of -2.

This is how you find the ionic charge of the first 20 elements. Cheers.

Enjoy!


Entry by
Json Lim
www.oleveltuition.com