Question

1. The coordination number of anions in a crystal of CaF2 is 4. What is the coordination number of cations?

2. What is the symbol for the ion that contains 20 protons, 18 electrons, and 20 neutrons?

A) 40Ca^2+

B) 20Ca^2+

C) 40Ca^1+

D) 40 Zr^2+

Answer 1

1.

General ionic structures are described by two coordination numbers, one for each type of ion.

Calcium fluoride (CaF2) is an (8, 4) structure, meaning that each cation Ca²⁺ is surrounded by eight F⁻ anion neighbors, and each anion F⁻ by four Ca²⁺. So coordination number of Ca⁺² and F^- ion in CaF2 crystal are 8 and 4 respectively.

2.

Atomic number of calcium, Ca = 20

So, the number of electron = number of protron = 20

After loosing 2 electrons, total eletrons in Ca is 18 and it gets +2 charge.

So, answer is (A) 40Ca^2+