The attraction of each electron in an atom is unique. This is due to the charge on the nucleus, the distance and repulsion by other electrons. Ionization Energy: The work required to remove an electron from an atom. No two electins in an atom have the same value. This increases at certain stages leading to the energy shell model of the atom. Electronegativity: The number describing a particle's ability to retain an electron in a chemical reaction. It describes and predicts the degree of polarity of a chemical bond. (grades 11-12).