How to find the valency of a compound

Valency is the number of electrons an atom needs to gain, lose, or share to achieve a stable electron configuration, usually like that of a noble gas.

To find the valency of a compound:

1. Identify the elements: Determine the elements present in the compound.
2. Find individual valencies: Determine the valency of each individual element. This is often based on their position in the periodic table or common bonding patterns.
   • Group 1 elements (alkali metals) usually have a valency of 1.
   • Group 2 elements (alkaline earth metals) usually have a valency of 2.
   • Group 17 elements (halogens) usually have a valency of 1.
   • Group 16 elements usually have a valency of 2.
   • Group 13 elements usually have a valency of 3.
   • Group 14 elements can have valencies of 4.
   • Transition metals can have variable valencies.
3. Apply the rule of charge neutrality: In a neutral compound, the total positive charge must equal the total negative charge. The valency of an element in a compound is often represented by the magnitude of the charge it carries as an ion.

For example, in water (H₂O):

• Oxygen (Group 16) typically has a valency of 2.
• Hydrogen (Group 1) typically has a valency of 1.
• The compound is neutral. Two hydrogen atoms (each with valency 1) balance one oxygen atom (with valency 2).

In sodium chloride (NaCl):

• Sodium (Group 1) has a valency of 1.
• Chlorine (Group 17) has a valency of 1.
• One sodium atom (valency 1) balances one chlorine atom (valency 1).