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).