Bohr model helps determine number of electrons in outer shell. How atoms react with one another is dependent upon number of electrons in outer shell. In atom with one shell, outer shell is filled when it contains two electrons. Orbital is a volume of space where rapidly moving electrons are predicted to be found. An orbital has a characteristic energy state and a characteristic shape.
Molecules are atoms held together by chemical bonds.
Ionic bonds form when electrons are transferred from one atom to another. Losing or gaining electrons, atoms participating in ionic reactions fill outer shells, and are more stable. Attraction of oppositely charged ions holds the two atoms together in an ionic bond . Covalent bond results when two atoms share electrons so each atom has octet of electrons in outer shell. Cl - , sodium has been oxidized, chlorine has been reduced.