Here's why:
* Stability: Atoms strive for a stable configuration, typically having a full outer shell of electrons.
* Reactivity: Atoms with incomplete outer shells tend to be more reactive, seeking to gain, lose, or share electrons to achieve a stable configuration.
* Noble Gases: Noble gases (like Helium, Neon, Argon) are very unreactive because they already have a full outer shell.
Examples:
* Sodium (Na): Has 1 electron in its outer shell. It easily loses this electron to become a positively charged ion (Na+), becoming less reactive.
* Chlorine (Cl): Has 7 electrons in its outer shell. It readily gains an electron to become a negatively charged ion (Cl-), achieving a stable configuration and becoming less reactive.
Therefore, changing the number of electrons in the outermost shell directly influences an atom's reactivity.
