Here's why:
* Valence Shell: This is the outermost shell of electrons in an atom. It's the shell involved in chemical bonding.
* Nonmetals: These elements typically gain electrons to achieve a full valence shell. They are found on the right side of the periodic table (except for hydrogen).
Examples:
* Nitrogen (N): Has 5 valence electrons and needs 3 more to fill its shell.
* Oxygen (O): Has 6 valence electrons and needs 2 more to fill its shell.
* Chlorine (Cl): Has 7 valence electrons and needs 1 more to fill its shell.
Exceptions:
* Group 18 (Noble Gases): These elements have a full valence shell by definition. They are exceptionally unreactive because they don't need to gain or lose electrons.
* Some nonmetals in Group 17 (Halogens) and Group 16 (Chalcogens): Can form covalent bonds by sharing electrons, which can lead to a situation where they do not have a completely full valence shell.
Key Points:
* Nonmetals tend to gain electrons to achieve a stable, full valence shell.
* The goal is to achieve the electron configuration of a noble gas.
* Some nonmetals can form covalent bonds and share electrons, which can leave their valence shell partially filled.
