ABSTRACT

Electropositive atoms, such as alkali atoms, tend to donate the weakly bound electrons of their valence shell to electronegative atoms, such as halogens, which tend to accept electrons in the empty valence orbitals, thereby completing the shell for both ions. Ordinary rock salt (NaCl) thus consists of positive ions (Na+) and negative ions (Cl−). In NaCl, one orbital is a linear combination of 3p orbitals of the liganding Cl− ions, all pointing inward toward the sodium ion. This orbital reminds of the 3s orbital in Na, but is considerably smaller, thus allowing the Na+ and Cl− ions to come closer and increase the ionic binding energy.