Chemistry - Atoms, elements, and compounds (Atomic structure and bonding)

Atoms consist of a central nucleus containing protons ($p^+$) and neutrons ($n^0$), surrounded by electrons ($e^-$) orbiting in shells or energy levels.

The Atomic Number ($Z$) is the number of protons in the nucleus; the Nucleon Number ($A$), or Mass Number, is the total number of protons and neutrons.

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, such as $^{35}_{17}Cl$ and $^{37}_{17}Cl$.

The electronic configuration follows the $2, 8, 8$ rule for the first 20 elements, where the outer shell electrons determine chemical properties.

Ionic Bonding occurs between metals and non-metals through the transfer of electrons, resulting in electrostatic attraction between oppositely charged ions like $Na^+$ and $Cl^-$.

Covalent Bonding occurs between non-metals through the sharing of electron pairs to achieve a stable outer shell, forming molecules like $CH_4$ or $H_2O$.

Metallic Bonding is the electrostatic attraction between a lattice of positive metal ions and a 'sea' of delocalized electrons.

Noble gases (Group VIII/0) are unreactive because they possess a full outer shell of electrons (a stable octet, or duplet for $He$).