Definition of Valency
Valency in chemistry refers to the combining capacity of an element, indicating how many bonds an atom of that element can form. It represents the number of hydrogen atoms that an atom of an element can combine with or displace, or, more broadly, the number of electrons an atom needs to gain, lose, or share to achieve a stable electron configuration.
How Valency is Determined
An atom's valency is primarily determined by the number of electrons in its outermost shell, known as valence electrons. Atoms tend to react in ways that allow them to achieve a stable electron configuration, typically an octet (eight valence electrons) or a duet (two valence electrons for hydrogen and helium). The number of electrons an atom gains, loses, or shares to reach this stability is its valency.
Valency in Action: Examples
For instance, hydrogen has one valence electron and needs one more to complete its duet, so its valency is 1. Oxygen has six valence electrons and needs two more for an octet, giving it a valency of 2. Carbon has four valence electrons and needs four more, resulting in a valency of 4. This explains why water is H₂O (two hydrogens with valency 1 combining with one oxygen with valency 2), and methane is CH₄ (one carbon with valency 4 combining with four hydrogens with valency 1).
Importance in Chemical Bonding
Understanding valency is crucial for predicting the chemical formulas of compounds and comprehending how atoms interact to form molecules. It provides a simple rule for determining the ratios in which elements combine, allowing chemists to predict the structure and properties of countless substances. It's a foundational concept for studying all types of chemical bonds, including ionic and covalent bonds.