Question

What are the $17$ nonmetals on the periodic table?

Answer 1

In addition to noble gases, the nonmetals complete their octet by accepting electrons. Most of the nonmetals are placed at the right hand side of the periodic table.

Complete step by step answer:
There is no accepted definition of nonmetal. Generally an element which lacks the properties of metal, can be a nonmetal.
Following criteria can help to identify nonmetals:
Only one element from s-block , i.e., hydrogen is nonmetal.
Most of the nonmetals have high electronegativity, thus they are located in p-block, towards the end of different periods of periodic table.
All noble gases are nonmetals.
Based on the above criteria, we can remember that following $17$elements are classified as nonmetals:
One element in the group $1$, i.e., hydrogen (${\text{H}}$).
One element in the group $14$, i.e., carbon (${\text{C}}$).
Two elements in the group $15$, i.e., nitrogen (${\text{N}}$)and phosphorous (${\text{P}}$).
Three elements in group $16$, i.e., oxygen (${\text{O}}$), sulphur (${\text{S}}$) and selenium (${\text{Se}}$).
Four elements in group $17$, i.e., fluorine (${\text{F}}$), chlorine (${\text{Cl}}$), bromine (${\text{Br}}$) and iodine (${\text{I}}$).
Six elements of group $18$, i.e., helium (${\text{He}}$), neon (${\text{Ne}}$), argon (${\text{Ar}}$), krypton (${\text{Kr}}$), xenon (${\text{Xe}}$) and radon (${\text{Rn}}$).

Additional Information:
Nonmetals have following physical properties:
Brittle in solid state
Low density
Low melting and boiling point
Poor thermal and electrical conductivity
High ionization energy and

Note: Metalloids should not be confused with nonmetals. They have properties between metals and nonmetals. These are boron (${\text{B}}$), silicon (${\text{Si}}$), germanium (${\text{Ge}}$), arsenic (${\text{As}}$), antimony (${\text{Sb}}$), tellurium (${\text{Te}}$) and astatine (${\text{At}}$).