Having 8 valence electrons is stable because it achieves a full electron shell, resembling a noble gas configuration.
The Octet Rule and Stability
The octet rule is the guiding principle here: atoms "want" to have 8 valence electrons. They achieve this by forming chemical bonds. Why 8? Because having 8 valence electrons completes the outermost electron shell for most atoms, resulting in a significantly stable state. According to the reference, atoms will tend to form compounds that give them 8 valence electrons; the reason for 8 is that it completes a full shell, which is the most stable configuration (noble gas config).
Electron Shells and Energy Levels
Electrons occupy specific energy levels, or shells, around an atom's nucleus. The first shell can hold up to 2 electrons, and subsequent shells (second, third, etc.) can ideally hold up to 8 electrons. When a shell is "full," the atom becomes exceptionally stable.
Noble Gas Configuration
Noble gases (Helium, Neon, Argon, Krypton, Xenon, and Radon) already have full valence shells. Helium has 2 valence electrons (filling its first shell), while the rest have 8. This is why they are so unreactive; they don't need to gain, lose, or share electrons to become stable. Atoms strive to achieve this noble gas configuration through bonding.
Examples
- Sodium Chloride (NaCl): Sodium (Na) readily loses one electron to become Na+, achieving a full outer shell. Chlorine (Cl) readily gains one electron to become Cl-, also achieving a full outer shell of 8. Both ions now have a stable noble gas configuration.
- Methane (CH4): Carbon (C) shares four electrons with four Hydrogen (H) atoms. Carbon ends up with 8 valence electrons (4 of its own + 4 from the hydrogens), and each hydrogen atom ends up with 2 valence electrons, achieving stable configurations.
In essence, the stability associated with having 8 valence electrons arises from the completed outer electron shell, mirroring the stable electron configurations of noble gases.
