# Nonmetals

Nonmetals can be found in groups 14–17 and all of group 18. Nonmetals tend to have properties opposite of metals: they often have low melting and boiling points, conduct electricity poorly, have high ionization energy, and generally have high electronegativity.

Chemically, nonmetals have high ionization energies so they do not give electrons away easily. Compared to metals, nonmetals have high electronegativity values, which indicates a tendency to strongly pull electrons. For these reasons, when nonmetals react with metals, they generally form ionic compounds. When nonmetals react with other nonmetals, they generally form covalent compounds.

Hydrogen is the lightest element on the periodic table and the only nonmetal element found outside groups 14–17. Hydrogen is the chemical element with the atomic number of 1. It is the smallest, lightest element and the most common atom in the universe. Hydrogen atoms are often part of other compounds. Under standard temperature and pressure, hydrogen atoms react with each other to form hydrogen gas, H2, a diatomic element. Hydrogen gas is highly flammable. Hydrogen is composed of one electron and one proton, and most hydrogen atoms do not contain neutrons. If a hydrogen atom loses its electron, the hydrogen ion (H+) that is formed is a proton.

Hydrogen is commonly produced from methane (CH4) and steam (H2O). At high temperatures, the following reaction takes place:
${\rm{CH}}_4(g)+{2{\rm H}_2\rm O}(g)\rightarrow{\rm{CO}}_2(g)+4{\rm H}_2(g)$
Hydrogen is important for synthesis of ammonia (NH3) and in the petroleum industry for processing fossil fuels.

Sulfur is an important element because sulfuric acid is the most commonly used commercial compound in the world, used in artificial fertilizers, detergents, lead-acid automobile batteries, and more. Sulfur is an element from group 16 and has six valence electrons, like oxygen. In compounds, sulfur commonly takes either a –2 or +6 oxidation state. Sulfur commonly takes a +6 oxidation state in compounds with electronegative atoms, such as fluorine. Sulfur has many allotropes. An allotrope is one of the possible physical forms in which an element can exist. The most common allotrope of sulfur is a ring of eight sulfur atoms. In this form, sulfur is a yellow solid at room temperature.

Sulfur was traditionally mined. There are multiple minerals that contain sulfur, with pyrite being a common one. It could even be found in almost pure elemental form in certain locations. Today, most sulfur is obtained from oil and natural gas. Crude oil and natural gas have sulfur atoms bonded to carbons. The carbon-sulfur bonds can be broken, and sulfur can be recovered as hydrogen sulfide (H2S).