How do you find out the number of bonds that an element can make?

Question

example:

carbon is said to have FOUR bonds

where do you find that information?

Answer 1

A carbon will have 4 bonds because it wants to have 8 valence electrons in it's outermost shell, which would satisfy the octet rule.  This forms a stable electron configuration similar to noble gas elements ( Ne, Ar, Kr, Xe...)  Since there are two electrons involved in each bond, 4 bonds would equal 8 electrons.  This is more easily seen if you write the compound in a Lewis structure, because each electron is shown.  Some exceptions to the octet rule include H, which only has 2 valence electrons in its outermost shell, and elements found in or beyond the 3rd period of the periodic table can have more than 8 valence electrons because some of the valence electrons occupy the d orbital.

For example, in the compound CH4,  all four H's would be attached to the central Carbon.  That would give 4 bonds to the carbon (2 electrons for each bond = 8 valence electrons = satisfied octet rule) and one bond to each of the hydrogens.  Remember, that H only needs 2 electrons, and since there is only one bond (2 electrons) between the H and C, then H is stable.