The ionic substances NaF, CaO, and ScN are isoelectronic (they have the same number of electrons). Examine the lattice energies for these substances in Table 8.2. Make a graph of lattice energy on the vertical axis versus the charge on the cation on the horizontal axis.

(a) What is the slope of the line?

(b) Make a graph of lattice energy on the vertical axis versus the square of the cation charge on the horizontal axis. What is the slope of this line?

(c) Compare how well the data points fall on a line for the graphs in (a) and (b). Which trend is more linear, lattice energy versus cation charge or lattice energy versus cation charge squared?

(d) Predict the lattice energy for the compound TiC, if we consider the carbon to have a 4^- charge.

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Table 8.2 Lattice Energies for Some Ionic Compounds Lattice Energy (回/mol) Lattice Energy (kJ/mol) Compound Compound LiF 1030 MgCl, 2326 LicI 834 SrCl, 2127 Lil 730 NaF 910 Mgo 3795 NaCl 788 Cao 3414 Na Br 732 SrO 3217 Nal 682 KF 808 ScN 7547 KCI 701 KBr 671 CSCI 657 CsI 600