Atomic Structure — Practice Quiz

3

Valency is defined as the number of hydrogen atoms that combine with one atom of an element. In ammonia (NH₃), one nitrogen atom combines with 3 hydrogen atoms. Therefore, the valency of nitrogen is 3. Carbon in methane (CH₄) has valency 4, oxygen in water (H₂O) has valency 2, and chlorine in HCl has valency 1. This concept helps us understand how atoms bond together.

CaCl₂

To find the formula: Calcium (Ca) has valency 2 and Chloride (Cl) has valency 1. Using the cross-multiplication method, we interchange the valencies: Ca gets subscript 1 (ignored) and Cl gets subscript 2. So the formula is CaCl₂. CaCl is wrong because it does not balance the valencies. Ca₂Cl₂ is incorrect because it can be simplified to CaCl₂. Ca₂Cl reverses the subscripts incorrectly.

Argon

Argon (Ar) is a noble gas (inert gas) present in Group Zero of the Periodic Table. Noble gases have completely filled electron shells, which means they do not need to combine with other atoms. Hence their valency (combining capacity) is zero. Oxygen has valency 2, Nitrogen has valency 3, and Fluorine has valency 1. Noble gases like Helium, Neon, and Argon all have zero valency.

Cation

Radicals (ions) are of two types based on their charge. A radical with a positive charge is called a cation (also known as a basic radical). Cations are formed when an atom loses electrons. For example, Na⁺ (sodium ion) is a cation. An anion (or acid radical) carries a negative charge and is formed when an atom gains electrons. For example, Cl⁻ is an anion. Neutron is a subatomic particle, not a type of radical.