Valence are the electrons located in the outermost shell of an atom. Because they are attracted to the nucleus by a weak force, they are easily attracted to other valence electrons of other atoms.
The Lewis structure of the methyl ion is shown in the picture. As stated in the Octet Rule, each element (except exceptions like Hydrogen) must have 8 electrons surrounding them. Each single bond contains 2 electrons. Therefore, there are only two electrons in the valence shell.
