Chapter 1 - Additional Exercises - Page 51d: 55

a. phosphorus 15 protons 16 neutrons b. iodine. 53 protons 74 neutrons c. potassium 19 protons 20 neutrons d. ytterbium 70 protons 103 neutrons

a. This element with an atomic number of 15 is phosphorus. We know this because the subscript on the left-hand side of the chemical symbol denotes the atomic number as well as the number of protons. Therefore, this atom contains 15 protons. To figure out the number of neutrons in this atom, we use the mass number, which is the superscript to the left of the element's chemical symbol. Because the mass number if the number of protons plus the number of neutrons, we merely subtract the number of protons or atomic number (15) from the mass number (31) to get the number of neutrons (16). b. The element with an atomic number of 53 is iodine. We know this because the subscript on the left-hand side of the chemical symbol denotes the atomic number as well as the number of protons. Therefore, this atom contains 53 protons. To figure out the number of neutrons in this atom, we use the mass number, which is the superscript to the left of the element's chemical symbol. Because the mass number if the number of protons plus the number of neutrons, we merely subtract the number of protons or atomic number (53) from the mass number (127) to get the number of neutrons (74). c. The element with an atomic number of 19 is potassium. We know this because the subscript on the left-hand side of the chemical symbol denotes the atomic number as well as the number of protons. Therefore, this atom contains 19 protons. To figure out the number of neutrons in this atom, we use the mass number, which is the superscript to the left of the element's chemical symbol. Because the mass number if the number of protons plus the number of neutrons, we merely subtract the number of protons or atomic number (19) from the mass number (39) to get the number of neutrons (20). d. The element with an atomic number of 70 is ytterbium. We know this because the subscript on the left-hand side of the chemical symbol denotes the atomic number as well as the number of protons. Therefore, this atom contains 70 protons. To figure out the number of neutrons in this atom, we use the mass number, which is the superscript to the left of the element's chemical symbol. Because the mass number if the number of protons plus the number of neutrons, we merely subtract the number of protons or atomic number (70) from the mass number (173) to get the number of neutrons (103).