Nonmetals
The elements are divided into two main types, metals and nonmetals, based on their properties. The nonmetals are located on the upper right side of the periodic table. Only eighteen elements in the periodic table are generally considered asnonmetals. But nonmetals make up most of the crust, atmosphere and oceans of the earth. Bulk tissues of living organisms are composed almost entirely of nonmetals. The elements generally considered as nonmetals are:
- In Group 1: hydrogen (H) (the only nonmetal in this group)
- In Group 14: carbon (C) (the only nonmetal in this group)
- In Group 15: (the pnictogens): nitrogen (N), phosphorus (P)
- In Group 16: (the chalcogens): oxygen (O), sulfur (S), selenium (Se)
- In Group 17: (the halogens): fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At)
- All elements (with the possible exception of ununoctium) in Group 18 – the noble gases
Common properties of nonmetals:
Mostly gases at room temperature
Weak, dull, and brittle when solids
Poor conductors of heat
Poor conductors of electricity
Most have low melting point (except carbon)
Most have low boiling point
Low densities
Nonmetals form acidic oxides
Insulators (except graphite)
Nonmetals have high electronegativity
Nonmetals have high ionization energies
Most nonmetals are monatomic noble gases or form diatomic molecules in their elemental state, unlike metals which (in their elemental state) do not form molecules at all.