Lattice energy is the a measure of how strong an ionic bond is. An ionic bond is the joining together of two electrically charged atoms called ions in order to form a compound. A common example of a compound formed from an ionic bond is table salt, sodium chlorine NaCl. The Born-Lande equation is used to find the lattice energy of a compound, and the formula for the equation is E = [-(NA)(M)(Z+)(Z-)/4(pi)(e0)(r0)][1-(1/n)]. While this may look exceedingly complicated, most of the equation is constants, meaning the values are the same every time.

Plug in the constants. The constants in the equation are NA which is the symbol for Avogadro's constant 6.02214179(30)×10^23 mol; e, the elementary charge 1.602176487(40)×10^-19 c), and e0, the permittivity of free space, 8.854×10^−12 c^2 J^−1 mol^−1.

Fill in the variables that change depending on the compound. The information that needs to be given is the Madelung constant represented as M, which, despite being called a "constant," as it is indeed constant within the compound itself, is different for each compound; the charge of the positive ion also called a cation, represented as Z+; the charge of the negative ion also called an anion, and shown as Z-; the distance to the nearest ion, shown as r0, and the Born exponent, represented as n, which is a number between 5 and 12.

Solve the equation. The final value of lattice energy should be in kilojoules per mole.

#### Warning

Be sure not to lose the negative at the beginning of the equation. The final number for the lattice energy of a compound should always be negative.