Question

What is the distribution of electrons in a Magnesium atom?
a) (2,8,1)
b) (2,8,2)
c) (2,8,3)
d) (2,8,4)

Answer 1

Hint: This question is based on the principle of electron filling in an atom. Bohr-Bury scheme will be used to find out the electron distribution in a Magnesium atom. According to the Bohr-Bury scheme maximum number of electrons in an orbit will be $2{{n} ^{2}}$. So this formula will be used to find out the number of electrons will be filled in an orbit starting from first orbit and in the last orbit the remaining electrons will be filled and that number may be less than its maximum capacity of accommodating electrons.

Complete step by step answer:
As we know that the atomic number of Magnesium is 12, so total 12 electrons will be distributed in a Magnesium atom.
As maximum number of electrons in an orbit = $2{{n}^{2}}$
- Number of electrons in first orbit = $2(1){}^{2}$
Number of electrons in first orbit = 2
- Number of electrons in second orbit = $2{{(2)}^{2}}$
- Number of electrons in second orbit = $2\times 4$
Number of electrons in second orbit = 8
As a total 10 electrons are present in first and second orbit, where 2 electrons are in first orbit and 8 electrons in second orbit and atomic number of Magnesium is 12, so only 2 electrons will be present in third orbit.
So, electron distribution in Magnesium atom will be (2, 8, 2)

The correct answer is option “B” .

Additional Information:
- Magnesium is highly reactive alkaline earth metal. It is present in the third period and second group of periodic tables. Elements of this second group are called alkaline earth metal because they form a basic solution when dissolved in water.
- Magnesium reacts with hot water to form Magnesium hydroxide along with hydrogen gas.
\[Mg+2H{}_{2}O(hot)\to Mg{{(OH)}_{2}}+{{H}_{2}}(gas)\]
- Solution of Magnesium Hydroxide is called Milk of magnesia and it is a very good antacid.
With steam Magnesium forms its oxide along with hydrogen gas.
\[Mg+{{H}_{2}}O(steam)\to MgO+{{H}_{2}}(gas)\]

Note: Magnesium is a metal having only 2 electrons in its outermost shell so in chemical reactions with nonmetals it will have the tendency to lose these two electrons, that’s its valency is 2 and it forms a divalent cation. As we know, the atomic number of Magnesium is 12, so the total number of electrons in a Magnesium atom will be 12. Among all options only Option (B) has 12 electrons. Therefore the correct answer can only be Option (B). This is the short trick to solve this question.