Definition of valence. A study of the formulas of various binary compounds shows that the elements differ between themselves in the number of atoms of other elements which they are able to hold in combination. This is illustrated in the formulas
| HCl, | H2O, | H3N, | H4C. |
| (hydrochloric acid) | (water) | (ammonia) | (marsh gas) |
It will be noticed that while one atom of chlorine combines with one atom of hydrogen, an atom of oxygen combines with two, an atom of nitrogen with three, one of carbon with four. The number which expresses this combining ratio between atoms is a definite property of each element and is called its valence.
DEFINITION: The valence of an element is that property which determines the number of the atoms of another element which its atom can hold in combination.
