An atom that gains one or more electrons has been reduced and forms an anion. Anions have a negative charge. Positively charged cations are attracted to negatively charged anions and this attraction is what holds the ionic bond together. With ionic compounds, the positive and negative charges must be balanced. Covalent bonds form between nonmetals.
Covalent bonds form through the sharing of valence electrons.
Hydrogen bonds result from electrostatic attraction between oppositely charged portions of neighboring polar molecules. Van der Waals interactions are much weaker than ionic or hydrogen bonds and occur between electrically neutral molecules or parts of molecules. Hydrophobic bonds result when nonpolar molecules are mixed with polar molecules, particularly water. Hydrogen bonds between water molecules result in strong ordering of the molecules. This ordering results in physical properties such as high surface tension, high boiling point, high melting point, high heat capacity and high heat of vaporization.