How does an atom's electronegativity change as it becomes more negatively charged? I had a question about the carbon atom specifically. Carbon has 4 valence electrons, with electronegativity 2.55 (approx). If I was to fire electrons at the carbon atom, each carbon will occupy up to 4 electrons (8 in total in outer shell) to complete the octet. Now, let's assume that this happens slowly such that we have time to observe each carbon atom as it changes its charge, from $\ce{C-, C^2-, C^3-, C^4-}$

My question is: how would the electronegativity of the carbon ions will vary from each other? Will it increase as electrons are added and becomes zero after obtaining full octet? What would happen upon taking away electrons from carbons through help of highly electronegative elements?
Electronegativity is a measure of the ability of an atom to attract electrons to itself (usually in a bonding framework; outside of a bonding framework the ability to attract electrons is electron affinity). 

So from simple Coulombic considerations, we can surmise that as your carbon becomes more and more negatively charged, the less it will be able to attract electrons to itself.