CBSE Class 10 Science 2017 · Paper 31/2/1 · Question 8

Carbon (atomic number 6) has the configuration 2, 4, with four valence electrons, so it would have to gain or lose four electrons to attain a noble gas configuration. It does not form ${\text{C}}^{4-}$: gaining four electrons would be difficult, because a nucleus with six protons cannot easily hold on to ten electrons. It does not form ${\text{C}}^{4+}$: losing four electrons would require a large amount of energy, and would leave six protons holding on to just two electrons. Instead, carbon shares its four valence electrons with other atoms and forms covalent bonds. Since the electrons are shared and no ions are formed, such covalent compounds are poor conductors of electricity. The bonds within their molecules are strong, but the forces of attraction between the molecules are weak, so they have low melting and boiling points.