Understanding Ionic Compounds
* Ionic Bonds: Ionic compounds are formed when a metal atom (like sodium or calcium) donates one or more electrons to a nonmetal atom. This transfer of electrons creates positively charged ions (cations) and negatively charged ions (anions). The opposite charges attract, forming a strong electrostatic bond.
Sodium (Na)
* Sodium Ion (Na+): Sodium is in Group 1 of the periodic table, meaning it has one valence electron (electron in its outermost shell). It readily loses this electron to achieve a stable electron configuration. When it loses the electron, it becomes a positively charged ion (Na+).
Calcium (Ca)
* Calcium Ion (Ca2+): Calcium is in Group 2 of the periodic table, having two valence electrons. It loses both of these electrons to become a stable ion, forming a +2 charge (Ca2+).
Forming Ionic Compounds
Ionic compounds always contain both a cation (positive ion) and an anion (negative ion). To predict the formula of an ionic compound, you need to consider the charges of the ions involved:
* Sodium Chloride (NaCl): Sodium (Na+) combines with chlorine (Cl-), which gains an electron to form a -1 charge. The charges balance out, resulting in a 1:1 ratio of ions in the compound.
* Calcium Chloride (CaCl2): Calcium (Ca2+) combines with chlorine (Cl-). To balance the +2 charge of calcium, two chloride ions are needed (-1 each).
* Sodium Oxide (Na2O): Sodium (Na+) combines with oxygen (O2-), which gains two electrons to form a -2 charge. Two sodium ions are needed to balance the -2 charge of the oxide ion.
Key Points
* Predicting Formulas: The number of each ion in the formula is determined by the charges of the ions to ensure a neutral overall charge.
* Empirical Formulas: Ionic compound formulas are usually empirical formulas, meaning they represent the simplest whole-number ratio of ions in the compound.
* Crystalline Structures: Ionic compounds form crystal lattices where the ions are arranged in a repeating pattern.
