## Chemistry: Principles and Practice (3rd Edition)

(a) $^{16}_{8}$O$^{2-}$ (b) $^{79}_{34}$Se$^{2-}$ (c) $^{59}_{28}$Ni$^{2+}$
(a) The element with 8 protons in the nucleus, which means the atomic number is 8, is oxygen, chemical symbol O. The superscript to the left of the chemical symbol would be the mass number, which is the total number of protons and neutrons in the nucleus of that atom. We add the number of protons, 8, to the number of neutrons, 8, to get a mass number of 16. The left subscript is the atomic number, which is 8. The superscript to the right of the chemical symbol is the charge of the ion. We figure this out by adding up the negative and positive charges to get a net charge. There are 8 protons, each with a single positive charge for a total charge of +8. The number of electrons is 10, each with a single negative charge for a total charge of -10. We add +8 to -10 to get a net charge of -2. The symbol for this ion would be $^{16}_{8}$O$^{2-}$. (b) The element with 34 protons in the nucleus, which means the atomic number is 34, is selenium, chemical symbol Se. The superscript to the left of the chemical symbol would be the mass number, which is the total number of protons and neutrons in the nucleus of that atom. We add the number of protons, 34, to the number of neutrons, 45, to get a mass number of 79. The left subscript is the atomic number, which is 34. The superscript to the right of the chemical symbol is the charge of the ion. We figure this out by adding up the negative and positive charges to get a net charge. There are 34 protons, each with a single positive charge for a total charge of +34. The number of electrons is 36, each with a single negative charge for a total charge of -36. We add +34 to -36 to get a net charge of -2. The symbol for this ion would be $^{79}_{34}$Se$^{2-}$. (c) The element with 28 protons in the nucleus, which means the atomic number is 28, is nickel, chemical symbol Ni. The superscript to the left of the chemical symbol would be the mass number, which is the total number of protons and neutrons in the nucleus of that atom. We add the number of protons, 28, to the number of neutrons, 31, to get a mass number of 59. The left subscript is the atomic number, which is 28. The superscript to the right of the chemical symbol is the charge of the ion. We figure this out by adding up the negative and positive charges to get a net charge. There are 28 protons, each with a single positive charge for a total charge of +28. The number of electrons is 26, each with a single negative charge for a total charge of -26. We add +28 to -26 to get a net charge of +2. The symbol for this ion would be $^{59}_{28}$Ni$^{2+}$.