Chapter 2 - Atoms, Ions, and Molecules - Questions and Problems - Page 71: 22

(a) 5 protons 5 electrons 6 neutrons (b) 9 protons 9 electrons 10 neutrons (c) 53 protons 53 electrons 78 neutrons (d) 86 protons 86 electrons 136 neutrons

(a) To determine the number of protons in this atom, we must determine to what element this atom belongs. From the periodic table, we find that B is the chemical symbol for boron. Its atomic number is 5. Therefore, the number of protons in that atom is 5 because the atomic number is also the number of protons in that atom. In a neutral atom, the number of electrons equals the number of protons; thus, there are also 5 electrons in this atom. The mass number is the number of protons and the number of neutrons in the nucleus of the atom and is the superscript to the left of the chemical symbol. If we subtract the number of protons (5) from the mass number (11), we get the number of neutrons (6) in the atom. (b) To determine the number of protons in this atom, we must determine to what element this atom belongs. From the periodic table, we find that F is the chemical symbol for fluorine. Its atomic number is 9. Therefore, the number of protons in that atom is 9 because the atomic number is also the number of protons in that atom. In a neutral atom, the number of electrons equals the number of protons; thus, there are also 9 electrons in this atom. The mass number is the number of protons and the number of neutrons in the nucleus of the atom and is the superscript to the left of the chemical symbol. If we subtract the number of protons (9) from the mass number (19), we get the number of neutrons (10) in the atom. (c) To determine the number of protons in this atom, we must determine to what element this atom belongs. From the periodic table, we find that I is the chemical symbol for iodine. Its atomic number is 53. Therefore, the number of protons in that atom is 53 because the atomic number is also the number of protons in that atom. In a neutral atom, the number of electrons equals the number of protons; thus, there are also 53 electrons in this atom. The mass number is the number of protons and the number of neutrons in the nucleus of the atom and is the superscript to the left of the chemical symbol. If we subtract the number of protons (53) from the mass number (131), we get the number of neutrons (78) in the atom. (d) To determine the number of protons in this atom, we must determine to what element this atom belongs. From the periodic table, we find that Rn is the chemical symbol for radon. Its atomic number is 86. Therefore, the number of protons in that atom is 86 because the atomic number is also the number of protons in that atom. In a neutral atom, the number of electrons equals the number of protons; thus, there are also 86 electrons in this atom. The mass number is the number of protons and the number of neutrons in the nucleus of the atom and is the superscript to the left of the chemical symbol. If we subtract the number of protons (86) from the mass number (222), we get the number of neutrons (136) in the atom.