In the energy-level diagram, the electrons are place in accordance with the quantum chemistry principles: excited state- a state of a system at higher energy than the ground state. Ionization potential- the energy it takes to remove an electron from an atom or a molecule: the 1s electrons have the highest ionization potential, valence electrons- outer-shell electrons, valence shell- the energy level valence electrons are found in. Lewis dot structure- the symbol of an element surrounded by a number of dots equal to the number of electrons in the valence shell of the atom. Section 1. 2: lewis model of bonding: octet rule- group 1a-7a elements react to achieve an outer shell of eight valence electrons, atoms acquire completed valence shells in two ways, an atom may become ionic, gains electrons = anion. Loses electrons = cation: a positively charged ion (cation) and a negatively charged ion (anion) attract each other, which can lead to the formation of ionic crystals.