What is Valency? Definition, Meaning & Example
The number of electrons that an atom loses, gains, or shares when forming a chemical bond.
TL;DR: The number of electrons that an atom loses, gains, or shares when forming a chemical bond.
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Valency: The number of electrons that an atom loses, gains, or shares when forming a chemical bond.
Explanation
Valency determines an atom's ability to combine with other atoms to form compounds. Elements in the same group of the periodic table typically have the same valency. Hydrogen has a valency of 1, oxygen typically 2, nitrogen typically 3. An element with high valency in one state can have different valency in another state, such as iron which can have valencies of 2 or 3. Understanding valency helps predict how atoms will combine and predict the formulas of compounds. For example, because hydrogen has valency 1 and oxygen has valency 2, water must be H2O to balance the charges.
Example
Sodium has valency 1 and chlorine has valency 1, so they combine in a 1:1 ratio to form sodium chloride (NaCl). Calcium has valency 2 and chlorine has valency 1, so they combine in a 1:2 ratio to form calcium chloride (CaCl2).
Frequently Asked Questions
How does valency relate to the periodic table?
Elements in the same group (vertical column) of the periodic table have the same number of valence electrons and thus similar valencies.
Can an element have multiple valencies?
Yes, some elements like iron and copper can have different valencies in different compounds, depending on how many electrons they lose or share.
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