Valency and formula of some common compounds

Understanding Valency and Writing Chemical Formulas

In chemistry, atoms combine with other atoms to form compounds. But how do we know how many atoms should come together? This is where the concept of valency helps us.

What is Valency?

Valency refers to an atom’s ability to combine with other atoms. It indicates the number of electrons an atom can give up, accept, or share in order to reach a stable configuration. In most cases, atoms aim to have eight electrons in their outermost shell — a principle known as the octet rule.

Examples:

• Hydrogen contains one electron and requires one additional electron to achieve stability. So, its valency is 1.
• Oxygen has 6 electrons in the outer shell, and it needs 2 more. So, its valency is 2.
• Sodium has 1 electron in the outer shell and can lose it. So, its valency is 1.

Steps to Write a Chemical Formula

You can determine the formula of a compound by using these steps:

1. Write the chemical symbols of the elements involved.
2. Note down their respective valencies underneath the symbols.
3. Exchange the valency numbers and use them as subscripts for the opposite element.
4. Reduce the subscripts to the simplest whole-number ratio, if needed.

Examples:

• Water (H₂O): Hydrogen (valency 1), Oxygen (valency 2). Swap the numbers → H₂O
• Sodium Chloride (NaCl): Sodium (valency 1), Chlorine (valency 1) → NaCl
• Magnesium Chloride (MgCl₂): Magnesium (2), Chlorine (1) → MgCl₂

Why Valency is Important

• It helps us know how elements combine to form compounds.
• It helps in writing correct chemical formulas.
• It is useful in balancing chemical equations.

Valency is a basic and very important idea in chemistry. It explains how atoms form compounds and helps us write formulas correctly. Once you understand valency, it becomes easy to work with chemical reactions and equations.