An atom has electronic configuration 2, 8, 7. (a) What is the atomic number of this element? (b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.) (a) N(7) (b) F(9) (c) P(15) (d) Ar(18)

Answer: 

(a)

The number of electrons present in an atom is

⇒ 2+8+7 = 17.

Therefore, the atomic number of this element is 17 and the element is chlorine.

Cl (Z = 17) = 1s² 2s² 2p⁶ 3s² 3p⁵

(b) 

Answer: (b) F(9)

It would be chemically similar to F(9) with configuration as 2, 7.

Electronic configuration of Fluorine is,

F (Z = 9) = 1s² 2s² 2p⁵

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