So-called “designer solvents” named for this term are functionalized to make them task-specific. In the Debye–Hückel limiting law, the natural logarithm of the mean activity coefficient is proportional to the square root of a quantity named for this term. The quantity “square root of 12 over 12 minus coordination number, all minus one” defines the critical value of the ratio in compounds described by this term written as “r-sub-C over r-sub-A.” This term names room-temperature liquids such as BMIM-PF6 and EMIM. Compounds described by this term are described by Pauling’s five rules. The Born–Haber cycle calculates the lattice energy of compounds described by this term. For 10 points, name this term that describes bonds between two oppositely charged species (10[2])such as (10[1])sodium and chloride. (10[1])■END■ (10[1]0[1])