Question

Find the oxidation number of Magnesium in Magnesium Chloride:
(A) +1
(B) -1
(C) +2
(D) -2

Answer 1

Hint: Solve this question by summing the oxidation number of each element to 0 since this element has a net charge equal to zero. Assign a random variable ‘x’ for calculating oxidation number of Mg.

Complete step by step answer:
> The compound Magnesium Chloride has the chemical formula - \[MgC{{l}_{2}}\]. As we can see it is a neutral compound, therefore its net charge = 0.
> We can calculate the oxidation number of Magnesium by following methods.
1) Method 1 –
Chlorine is a group 17 element and needs only one electron to complete its octet. So, its oxidation number is -1.
Let the oxidation number of Magnesium be ‘x’.
Therefore, (x) + 2(-1) = 0
x = +2.
2) Method 2 –
Magnesium is a group 2 element with atomic number 12.
Its electronic configuration is \[[Ne]3{{s}^{2}}\].
As we can see, it can lose two electrons to gain the electronic configuration of Neon.
Therefore, its oxidation number will be +2. Therefore option (C) +2 is the correct answer.

Additional Information: The oxidation number of an atom or element is a number that indicates the total number of electrons lost or gained by it.

Note: There are certain rules for calculating oxidation number –
- Oxidation number of any free element is zero.
- Oxidation number for a monatomic ion is equal to the net charge on it.
- Hydrogen, in general, has an oxidation state equal to +1. However, it is -1 in forms of a compound with an element with lesser electronegativity.
- Alkali metals have oxidation number = +1
- Alkali earth metals have oxidation number = +2
- Halogens have oxidation number = -1
- Oxygen has an oxidation number = -2, but in case of peroxides, it is -1.