Question

The atom of an element has electronic configuration 2, 8, 8, 2.
(a) What is the atomic number of the element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers of elements are given in brackets)
He (2); O (8); Mg (12); K (19)
​Give reason for your choice.

Answer 1

The atomic number of the element is equal to the number of electrons present in one atom of the element. Therefore, in this case: atomic number = 2 + 8 + 8 + 2 = 20

It will be chemically similar to Magnesium (Mg), since both of them are placed in the same group, i.e. Group II, and elements in the same group have similar chemical properties.

Answer 2

Explanation:

• (a) It is given in the question that
• Atomic number is made by the electronic configuration (2, 8, 8, 2) as 2 + 8 + 8 + 2 = 20. The element that has 20 as the atomic number is calcium.
• (b) There are two electrons in the calcium’s outermost shell.
• So, there will be 1 electron in the outermost shell of Hydrogen (H). Oxygen will have 6 electrons in its outermost shell, so its valency is -2. Magnesium has 2 electrons and Potassium has 1 electron in the outermost shell.
• Among these, elements, only magnesium has +2 valency as that of calcium. So, magnesium is the only element that has the properties as that of calcium.