1. The problem statement, all variables and given/known data Hi! So I stumbled upon this simple "plug n' play" exercise in my Physics textbook. Basically it gives you certain molecules/atoms, and tells you to measure the Electric Charge, and its Mass. Pretty simple, but I hit upon some hickups. Anyway, let's get to it: Find the Electric Charge and Mass of the following (the answer must be written with 3 Significant Digits): a) H+ b) Na+ c) Cl- d) Ca2+ e) N3- f) N4+ g) The nucleus of an atom N h) H2O- 2. Relevant equations Proton (p): Mass: 1.67262*10-27 kg Electric Charge: +1.6021765*10-19 C Electron (e): Mass: 9.1094*10-26 kg Electric Charge: -1.6021765*10-19 C Neutron (n): Mass: 1.67493*10-27 kg Electric Charge: 0 3. The attempt at a solution (a) H has 1 proton, and 1 electron. H+ is positively charged, a cation, so that means the sole electron has left. Therefore: EC: +1.60*10-19 C Mass: 1.67*10-27 kg (b) And here's where I get stuck. Na has 11 protons and 11 electrons. Na+ is positively charged, meaning one electron has left, and so: EC: +1.60*10-19 C Mass: 10*me + 11*mp = 1.84*10-26 kg But the book's answer is 3.82*10-26 kg. Am I missing something? Any help is appreciated!