The numerical value of the charge on an ion (cation or anion), describing the number of bonds which can be formed by the ion. Valencies may be respresented in different ways, that is, descriptively (e.g. divalent), with numbers (e.g. 2-) or with roman numerals (e.g. II) and may or may not include description of the charge (- or +). Examples of valancies are sodium (Na+) which is monovalent or univalent and the carbonate ion (CO32-) which is divalent. Chrome can occur in -(II) to +(VI) valencies, but is most common in the elemental (0), divalent (II), trivalent (III) and hexavalent (VI) forms.