Physical Chemistry> cations are genrally smaller than the res...

cations are genrally smaller than the respective atom whereas the anions are generally larger ? illustrate with example .

queen , 6 Years ago

Grade 11

2 Answers

Khimraj

Last Activity: 6 Years ago

Example

size of Na⁺ is smaller than Na.

size of O^2- is greater than O.

Hope it clears....................

Rajdeep

Last Activity: 6 Years ago

HELLO THERE!

The answer to your question is relatively simple and does not need any high level knowledge.

Cations are smaller than their parent atom. A cation is formed when the parent atom (of a metal) loses electron(s), and hence becomes positively charged. However, the number of protons remain the same. So, the negative charge in the atom decreases while the positive charge remains the same (in the cation). This results in a greater nuclear pull on the valence shell of the cation, due to which the atomic radius (size of the cation) decreases. Hence, cations are smaller than parent atom.

Consider Iron as an example. When it loses 2 atoms to become Fe²⁺, size of Fe²⁺is smaller than that of Fe. When it loses an electron more to become Fe³⁺, then the size of Fe³⁺ is less than that of Fe²⁺ (as nuclear pull on the valence shell of Fe³⁺ is more) and Fe.

Anions are generally larger than the parent atom. The reason is just the opposite.

An anion is formed when the parent atom (of a non-metal) gains electron(s), and hence becomes negatively charged. However, the number of protons remain the same. So, the negative charge in the atom increases while the positive charge remains the same (in the anion). This creates a wobbling up of the atom (due to repulsion between the electrons), so the atom of anion increases in size. Hence, size of anion is larger than that of the parent atom.

Consider Chlorine as an example. When a chlorine atom loses an electron to form Cl^- ion, size of Cl^- is greater than that of a Cl atom.

HOPE IT IS CLEAR...

Thanks!