Why are Bismuth and Nitrogen Expected to Lose and Gain Electrons Respectively?

[everything]

This isn't a HW question per se, but it arose after doing a HW problem -- feel free to move if you feel it's necessary.

I sorted four elements into two categories:

Those expected to lose electrons (Bi and Ga)
and
Those expected to gain electrons (N and Br)

I'm having difficulties grasping this conceptually -- particularly why Bi and N are in different categories if they both have 5 valence electrons. I understand that N is more electronegative than Bi, but how do you determine when this (electronegativity) will result in a net loss or gain?

 

[jbsteele]

The key to understanding why Bi and N are in different categories is to look at their electronegativity. Electronegativity is a measure of how strongly an atom attracts electrons when it forms a chemical bond with another atom. Generally, atoms with higher electronegativities will tend to gain electrons in a reaction, while atoms with lower electronegativities will tend to lose electrons in a reaction. For example, nitrogen has an electronegativity of 3.04 and bismuth has an electronegativity of 2.02. This means that nitrogen is more electronegative than bismuth, and thus is more likely to gain electrons in a reaction. Therefore, nitrogen is expected to gain electrons, while bismuth is expected to lose electrons.