Chapter 2 - Atoms, Molecules, and Ions: Matter Starts Here - Problems - Page 70: 43

(a)

(a) To find out the number of electrons in this ion of fluorine (F), we first look for fluorine on the periodic table. Fluorine has an atomic number of 9, so it has 9 protons. In a neutral atom, the number of protons and electrons are equal. Since this ion of fluorine has an extra negative charge (or an extra electron), it actually has 10 electrons instead of the normal 9. (b) To find out the number of electrons in this ion of chlorine (Cl), we first look for chlorine on the periodic table. Chlorine has an atomic number of 17, so it has 17 protons. In a neutral atom, the number of protons and electrons are equal. Since this ion of fluorine has an extra negative charge (or an extra electron), it actually has 18 electrons instead of the normal 17. (c) To find out the number of electrons in this ion of bromine (Br), we first look for bromine on the periodic table. Bromine has an atomic number of 35, so it has 35 protons. In a neutral atom, the number of protons and electrons are equal. Since this ion of bromine has an extra negative charge (or an extra electron), it actually has 36 electrons instead of the normal 35. (d) To find out the number of electrons in this ion of iodine (I), we first look for iodine on the periodic table. Iodine has an atomic number of 53, so it has 53 protons. In a neutral atom, the number of protons and electrons are equal. Since this ion of iodine has an extra negative charge (or an extra electron), it actually has 54 electrons instead of the normal 53. Option (a) is the correct answer because F$^{-}$ has 10 electrons.