Nonmetals often share or gain electrons. The nonmetals in the periodic table increases as you move to the right and decreases as you go down. This is because, the smaller the atom, the reactive it gets due to less electron attached to the orbits of the atom. The reactivity of nonmetals is arranged in decreasing order.
Carbon
Nitrogen
Oxygen
Fluorine
Phosphorus
Sulfur
Chlorine
Selenium
Bromine
Iodine