Solution. Having lost its two original valence electrons, the Lewis electron dot diagram is just Ca 2+. Ca2+. The O 2− ion has gained two electrons in its valence shell, so its Lewis electron dot diagram is as follows: Test Yourself. The valence electron configuration of thallium, whose symbol is Tl, is 6 s2 5 d10 6 p1. As per the NCl3 lewis dot structure, nitrogen is the central atom that has 3 bonded pairs of electrons and one lone present on it. Hence the formula of NCl3 becomes AX 3 N 1 So, according to the VSEPR chart , if the molecule has the formula of AX 3 N 1 then the molecule shape of that molecule is trigonal pyramidal, and electron geometry is ... Lewis Dot Diagrams… Gilbert Lewis used a different model than Bohr, and he only showed the valence e- in it. His model is called the . Lewis dot structure . He put dots around the symbols so that we can . see. just the . valence electrons . for the elements (so we can easily see which e- are going to react) Lewis dot d...