Electron shells are important because they help determine how atoms can bond with each other.

Every atom has a specific way its electrons are arranged in layers, which are called shells, around its central part (nucleus).

These shells fill up in a certain order, following rules called the Aufbau principle.

1. Shell Structure:

• First Shell: Can hold up to 2 electrons.
• Second Shell: Can hold up to 8 electrons.
• Third Shell: Can hold up to 18 electrons, but it usually stays stable with just 8 in main-group elements.

2. Valency and Electron Configuration:

Valency is mainly about how many electrons are in the outer shell. These outer electrons are called valence electrons.

For example:

• Group 1 Elements (like Sodium, Na): They have 1 valence electron, so their valency is 1.
• Group 7 Elements (like Chlorine, Cl): They have 7 valence electrons, so their valency is 1 because they need 1 more electron.

3. Ionic and Covalent Bonds:

Atoms will either lose, gain, or share electrons to fill up their outer shell.

This can be seen in ionic bonds (like in table salt, NaCl). Here, Sodium (Na) loses 1 electron so it can look like Neon, a stable gas. Chlorine (Cl) then gains that electron.

By looking at these examples, we can understand how electron shells affect the valency of atoms and how they can form different types of bonds with each other.