## Chemistry: An Atoms-Focused Approach

Published by W. W. Norton & Company

# Chapter 2 - Atoms, Ions, and Molecules - Questions and Problems - Page 71: 21

#### Answer

(a) 6 protons 6 electrons 8 neutrons (b) 26 protons 26 electrons 33 neutrons (c) 38 protons 38 electrons 52 neutrons (d) 82 protons 82 electrons 128 neutrons

#### Work Step by Step

(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 C is the chemical symbol for carbon. Its atomic number is 6. Therefore, the number of protons in that atom is 6 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 6 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 (6) from the mass number (14), we get the number of neutrons (8) 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 Fe is the chemical symbol for iron. Its atomic number is 26. Therefore, the number of protons in that atom is 26 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 26 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 (26) from the mass number (59), we get the number of neutrons (33) 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 Sr is the chemical symbol for strontium. Its atomic number is 38. Therefore, the number of protons in that atom is 38 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 38 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 (38) from the mass number (90), we get the number of neutrons (52) 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 Pb is the chemical symbol for lead. Its atomic number is 82. Therefore, the number of protons in that atom is 82 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 82 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 (82) from the mass number (210), we get the number of neutrons (128) in the atom.

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