chemical
The atoms of a compound are held together by chemical bonds. Chemical bonds form when atoms share electrons. There are different types of chemical bonds, and they vary in how strongly they hold together the atoms of a compound. Two of the strongest types of bonds are covalent and ionic bonds. Covalent bonds form between atoms that have little if any difference in electronegativity, and result when atoms share electrons. Electronegativity is the power of an atom to attract electrons toward itself. Ionic bonds , in contrast, form between atoms that are significantly different in electronegativity. An ion is an atom that has gained or lost at least one electron. Ionic bonds form between ions of opposite charges.