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

(a) $_{28}^{59}$Ni (b) $_{74}^{184}$W
(a) To write the complete symbol, we first locate the element nickel on the periodic table. We see that its chemical symbol is Ni. We also know from the periodic table that its atomic number is 28. We write the atomic number to the left of the chemical symbol as a subscript. The mass number is the number of protons and the number of neutrons. The number of protons is the same number as the element's atomic number. The number of neutrons is already given in the problem. So we have the number of protons as 28 and the number of neutrons as 31. When we add 28 to 31, we get 59; this is the mass number. We write the mass number as a superscript to the left of the chemical symbol as well. The complete symbol for this particular atom of nickel is $_{28}^{59}$Ni. (b) To write the complete symbol, we first locate the element tungsten on the periodic table. We see that its chemical symbol is W. We also know from the periodic table that its atomic number is 74. We write the atomic number to the left of the chemical symbol as a subscript. The mass number is the number of protons and the number of neutrons. The number of protons is the same number as the element's atomic number. The number of neutrons is already given in the problem. So we have the number of protons as 74 and the number of neutrons as 110. When we add 74 to 110, we get 184; this is the mass number. We write the mass number as a superscript to the left of the chemical symbol as well. The complete symbol for this particular atom of tungsten is $_{74}^{184}$W.