## Chemistry: Molecular Approach (4th Edition)

From the periodic table, the atomic number of calcium is 20. Thus, the number of protons in calcium is 20. The number of electrons is equal to the number of protons. Calcium has a +2 charge, which means it will lose two electrons. So, the number of electrons in $\text{C}{{\text{a}}^{2+}}$ is 18. From the periodic table, the atomic number of beryllium is 4. Thus, the number of protons in beryllium is 4. The number of electrons is equal to the number of protons. Beryllium has a +2 charge, which means it will lose two electrons. So, the number of electrons in $\text{B}{{\text{e}}^{2+}}$ is 2. From the periodic table, the atomic number of selenium is 34. Thus, the number of protons in selenium is 34. The number of electrons is equal to the number of protons. Selenium has a −2 charge, which means it will gain two electrons. So, the number of electrons in $\text{S}{{\text{e}}^{2-}}$ is 36. From the periodic table, the atomic number of indium is 49. Thus, the number of protons in indium is 49. The number of electrons is equal to the number of protons. Indium has a +3 charge, which means it will lose three electrons. So, the number of electrons in $\text{I}{{\text{n}}^{3+}}$ is 46.