What is the difference between valence, and number of valence electrons?

Question

Mateo Aguilar · Accepted Answer

Valence electrons are the outermost electrons of an atom.

Here is a video which discusses how to draw Lewis structures for atoms showing their number of valence electrons.
Video from: Noel Pauller

Valence refers to the ability of an element to combine with other atoms. There are two competing definitions.

Valence is the maximum number of hydrogen or chlorine atoms that can combine with an atom of the element.
According to this (official) definition, the valence of carbon is four, because carbon can form CH₄ and CCl₄.
- Valence is the number of hydrogen atoms or twice the number of oxygen atoms that can combine with an atom of the element.
  Many chemists use the second definition. By this definition, carbon has more than one valence. The valence of carbon can be either two or four, because carbon forms CO and CO₂.
  
  According to the first definition, nitrogen has a valence of 4, because it forms NH₄⁺ ions.
  
  But nitrogen also forms NO and NH₃. According to the second definition, it also has valences of 2 and 3.

Peyton Adams · Answer

undefined Valence refers to the number of bonds an atom can form with other atoms, while the number of valence electrons refers to the number of electrons in the outermost shell of an atom, which determines its chemical properties and ability to form bonds.