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Valency in Chemistry

When elements participate in chemical reactions, they do so in fixed whole-number ratios. For instance, in the formation of HCl, one hydrogen atom combines with one chlorine atom—no other ratio is possible for this combination. In contrast, four hydrogen atoms bond with a single carbon atom to form methane (CH₄). This shows that carbon and chlorine each combine with hydrogen in specific proportions, meaning they have different combining capacities.

This combining capacity of an element is known as valency.

In simple terms, the valency of an element is the number of hydrogen atoms that will combine with or be replaced by one atom of that element in a chemical reaction. Put differently, valency represents the number of electrons an atom uses to form chemical bonds with other atoms—defining its overall ability to interact and form compounds.

In an atom, the electrons responsible for bonding are known as valence electrons. These are the electrons found in the outermost shell, also called the valence shell, and they determine how an element interacts chemically.

When an element combines with another element besides hydrogen, the ratio in which they combine is determined by their valency. For example, since both sodium (Na) and chlorine (Cl) have a valency of 1, one sodium atom will combine with one chlorine atom to form sodium chloride (NaCl). On the other hand, magnesium (Mg) has a valency of 2, meaning one magnesium atom will combine with two chlorine atoms to form magnesium chloride (MgCl₂).

Some Elements Have More Than One Valency

It is important to note that some elements can exhibit multiple valencies. For example, iron (Fe) has valencies of 2 and 3, while copper (Cu) can have valencies of 1 and 2. Here are the valencies of some common elements.

Element	Valency
Hydrogen	(-1), +1
Helium	0
Lithium	+1
Beryllium	+2
Boron	-3, +3
Carbon	(+2), +4
Nitrogen	-3, -2, -1, (+1), +2, +3, +4, +5
Oxygen	-2
Fluorine	-1, (+1)
Sodium	+1
Magnesium	+2
Aluminum	+3
Silicon	-4, (+2), +4
Phosphorus	-3, +1, +3, +5
Sulfur	-2, +2, +4, +6
Chlorine	-1, +1, (+2), +3, (+4), +5, +7
Iron	+2, +3, (+4), (+6)
Cobalt	+2, +3, (+4)
Nickel	(+1), +2, (+3), (+4)
Copper	+1, +2, (+3)
Zinc	+2
Tin	+2, +4
Antimony	-3, +3, (+4), +5
Tellurium	-2, (+2), +4, +6
Iodine	-1, +1, (+3), (+4), +5, +7

What Determines Valency?

The valency of an element is determined by the number of electrons its atoms must lose, gain, or share to achieve a stable electronic structure similar to the nearest noble gas.

For instance:

• Sodium (Na) and Lithium (Li) each need to lose one electron to attain stability, giving them a valency of 1.

• Magnesium (Mg) needs to lose two electrons, so its valency is 2.

• Chlorine (Cl) must gain one electron, giving it a valency of 1.

• Sulfur (S) must gain two electrons, meaning its valency is 2.

Valency in Metals and Non-Metals

• For metals, the valency is equal to the number of electrons in the outermost shell.

• For non-metals, the valency is found by subtracting the number of outermost electrons from 8 (since non-metals tend to gain electrons to complete their octet).

• Noble gases, which already have a full outer shell, do not typically lose or gain electrons and are assigned a valency of zero.

The good news is that you don’t need to memorize all these methods for determining valency. As you continue studying and practicing chemistry, recognizing and recalling valencies will become easier. However, if you ever forget or get confused about the valency of a particular element, you can use our Valency Electron Calculator above. Simply enter the element’s symbol or name, and the calculator will instantly display its corresponding valency or valencies.