Carbon must gain four electrons to attain noble gas configuration. Carbon has a total of 6 electrons of which 4 are valence electrons. The four electrons are found in the outermost shell, for a stable configuration Carbon should gain four more electrons to give a 2.8 shell configuration. Most noble gases have 8 electrons in their outer shell with the exception of Helium. By gaining 4 electrons Carbon will have the same shell configuration as Neon.
