Chapter 2 - Sections 2.1-2.9 - Exercises - Problems by Topic - Page 81: 61

$Symbol \space \space \space \space \space Ion Formed \space \space \space \space \space Number\space \space \space \space \space electrons \space \space \space \space \space Number protons:$ $Ca \space \space \space \space \space Ca^{2+} \space \space \space \space \space 18 \space \space \space \space \space 20$ $Be \space \space \space \space \space Be^{2+} \space \space \space \space \space 2 \space \space \space \space \space 4$ $Se \space \space \space \space \space Se^{2-} \space \space \space \space \space 36 \space \space \space \space \space 34$ $In \space \space \space \space \space In^{3+} \space \space \space \space \space 46 \space \space \space \space \space 49$

Ca- because Calcium is an alkaline earth metal, it forms +2 cation which means it has two fewer electrons than protons. The atomic number for Calcium is 20 (which means it has 20 protons) and 20(protons)-2(fewer electrons than protons)= 18 electrons Be- Be$^{2+}$ means that the element is Be. Beryllium has two fewer electrons than protons, and because its ion has two electrons, it has 4 protons. Alternatively, you could just check what the atomic number for Be is. Se- Since Selenium is a Group 16 nonmetal, it forms a -2 anion which means it has two more electrons than protons. Selenium has 34 protons, and 34+2= 36 electrons In- Since Indium is group 13 post-transition metal, it forms a +3 cation which means it has three fewer electrons than protons. It has 49 protons and 49-3=46, an Indium ion has 46 electrons.