Ionic compounds

• What Is Lattice Energy in Ionic Compounds?
  Lattice energy measures the enthalpy change associated with forming an ionic solid from gaseous ions; its sign depends on the stated convention.
• Why Does Calcium Hydroxide Have Parentheses in Its Formula?
  Calcium hydroxide is written Ca(OH)₂ because two hydroxide ions are needed to balance calcium’s charge, so the parentheses group OH.