# Chapter 2 - Atoms, Molecules, and Ions - Questions and Exercises - Exercises - Page 87: 2.98

(a) Ca$_3$N$_2$ (b) Cr(ClO$_4$)$_3$ (c) SnF$_2$ (d) KMnO$_4$

#### Work Step by Step

(a) Ca$_3$N$_2$ According to the periodic table, calcium (Ca) is an alkaline earth metal and has a valence of 2+. Nitrogen (N), an element in group 15, has a valence of 3-. Therefore, we will need three calcium atoms for every two nitrogen atoms to balance the charges in this compound. (b) Cr(ClO$_4$)$_3$ Chromium (Cr) is a transition metal and has more than one valence; in this compound, chromium has a valence of 3+, as is evident by the Roman numeral III following its name. Perchlorate (ClO$_4$$^-), according to Table 2.2 on page 65 of our book, has a valence of 1-. Therefore, we will need one chromium atom for every three perchlorate ions to balance the charges in this compound. (c) SnF_2 Tin (Sn) is a transition metal and has more than one valence; in this compound, tin has a valence of 2+, as is evident by the Roman numeral II following its name. Fluorine (F), an element in group 17, has a valence of 1-. Therefore, we will need one tin atom for every two fluorine atoms to balance the charges in this compound. (d) KMnO_4 According to the periodic table, potassium (K) is an alkali metal and has a valence of 1+. Permanganate (MnO_4$$^-$), according to Table 2.2 on page 65 of our book, has a valence of 1-. Therefore, we will need one potassium atom for every one perchlorate ion to balance the charges in this compound.

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