## Organic Chemistry, 5th Edition

Published by McGraw-Hill Education

# Chapter 1 - Section 1.1 - The Periodic Table - Problem - Page 10: 1.1

#### Answer

a) Both isotopes have 7 protons b) Nitrogen -14 has 7 neutrons, and nitrogen -13 has 6 neutrons c) Both isotopes have 7 electrons d) Both isotopes belong to group 5A of the periodic table. e) Both isotopes have 5 valence electrons

#### Work Step by Step

Isotopes are two atoms of the same element having a different number of neutrons. Thus, the number of protons is the same between isotopes. The mass number ( protons + neutrons ) is the value given. Nitrogen-14 has a mass number of 14, and Nitrogen-13 has a mass number of 13. a) To determine the number of protons, look at the periodic table and locate the atomic number. This is the number present right above the letter. For Nitrogen the atomic number is 7. This means both isotopes of Nitrogen have a total of 7 protons. b) To determine the number of neutrons present in each isotope, simply subtract the atomic number of the atom from the given mass number of the isotope. Note : # Neutrons = Mass Number – Atomic Number # Neutrons of Nitrogen-14 = 14 - 7 = 7 # Neutrons of Nitrogen-13 = 13 - 7 = 6 c) The number of electrons in a neutral atom always equals the atomic number. The atomic number of both isotopes is 7, therefore the number of electrons in both isotopes is also 7. d) The group number of an atom can be found by looking for the number at the very top of the column of which the atom is present in. The group number is the same for all isotopes of the same atom. For nitrogen, the group number is 5A. e) Valence electrons are the outermost electrons of an atom. Nitrogen has the following orbitals, 1s, 2s, and three 2p orbitals. The outermost electrons in this case belong in the second row. Nitrogen has a total of 7 electrons, 2 of which are in 1s. This means that the remaining 5 electrons are in the second row making them the outermost electrons of an atom.

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