The combining capacity of an atom is known as its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.
An atom, ion, or chemical group with a valence of one, which thus can form one covalent bond is called monovalent.
Atoms that are monovalent are
An atom, ion, or chemical group with a valence of two, is called divalent.
Atoms that are divalent are
An atom, ion, or chemical group with a valence of three, is called trivalent.
Atoms that are trivalent are