definition of chemistry definition of periodic table

The two tables below show examples of different compounds, their structural formulas, and the valences for each element of the compound. The structural formula of a compound represents the connectivity of the atoms, with lines drawn between two atoms to represent bonds. Phosphorus has a valence 3 in phosphine ( PH 3) and a valence of 5 in phosphorus pentachloride ( PCl 5), which shows that an element may exhibit more than one valence. Chlorine, as it has a valence of one, can be substituted for hydrogen in many compounds. In methane, carbon has a valence of 4 in ammonia, nitrogen has a valence of 3 in water, oxygen has a valence of 2 and in hydrogen chloride, chlorine has a valence of 1. The valence is the combining capacity of an atom of a given element, determined by the number of hydrogen atoms that it combines with. Valence is not to be confused with the related concepts of the coordination number, the oxidation state, or the number of valence electrons for a given atom. In most compounds, the valence of hydrogen is 1, of oxygen is 2, of nitrogen is 3, and of carbon is 4.

Double bonds are considered to be two bonds, and triple bonds to be three. For a specified compound the valence of an atom is the number of bonds formed by the atom. Valence is generally understood to be the number of chemical bonds that each atom of a given element typically forms. In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules.

Definition of chemistry definition of periodic table