Just like all substances, ingredients, both man-made and those found in nature, are made from individual atoms of chemicals which are held together through chemical bonds.
The chemical bonds are caused by forces of attraction between the atoms and the strength of these attractions determines the strength of the bond.
One of the strongest types of chemical bond is a covalent bond. The other type of strong bond is an ionic bond. Covalent bonds and ionic bonds are the two types of chemical bond which hold the individual atoms of an ingredient together.