Ionic Compounds Notes

The octet rule states that atoms will gain or lose electrons in order to fill the outer valence level of eight electrons. Noble gases are the only elements that originally have complete octets, making them stable. Stability refers to how much potential energy an atom has. If something is very stable, it has a low potential energy level, and if something is not stable, it has a high potential energy level.

If an atom’s electron configuration is incomplete (and therefore unstable), it will either gain or lose electrons to become more stable. Doing this will release potential energy, resulting in a lower amount of energy left over.

Ionic Compounds Notes When atoms lose or gain electrons, they will gain or lose negative charge, becoming ions. The charge that any particular atom will tend to have as an ion can be predicted by the periodic table.

Ionic Compounds Notes Alkali metals will usually always form +1 charged ions, alkaline-earth metals will form +2 ions, and halogens will form -1 ions. Other groups that are somewhat predictable are: group 16 forms -2 ions group 15 forms -3 ions group 14 forms either +4 or -4 ions group 13 forms +3 ions

Ionic Compounds Notes Since ions have positive or negative charges, they can attract to each other and form chemical bonds called ionic bonds. The resulting compound can also be called a salt.

Ionic Compounds Notes Any bond that is formed between two atoms occurs because it lowers the amount of potential energy. When any bond is broken, the energy in the bond is released (called bond energy). The stronger the bond, the more energy that is released.

Ionic Compounds Notes The type of ion that any atom forms can be used to determine the ratio that it will be found in an ionic compound. Every ionic compound will balance out to have an overall neutral charge. Therefore, sodium (which forms a +1 ion) and chlorine (which forms a -1 ion) will have a 1:1 ratio in sodium chloride. What about calcium chloride? aluminum chloride?

Properties of Ionic Compounds An ion is an atom (or group of atoms!) that has a net charge (not zero). Any ion with a positive charge (less electrons than protons) is called a cation. Any ion that has a negative charge is called an anion.

Properties of Ionic Compounds When two oppositely charged ions are nearby, they are attracted to each other by electric forces. When they are close enough, they are held together by ionic bonds. They can then be called an ionic compound, or salt.

Properties of Ionic Compounds The electric forces in an Ionic bond are strong enough to hold more than one pair of opposite ions. Instead, they can form tightly packed structures called crystals, which have a “lattice” structure of alternating anions and cations.

Properties of Ionic Compounds Salts, when they are in their crystal form, do not melt or boil very easily because the ionic bonds are very strong. They are also very hard and brittle. Forming a lattice structure out of individual ions releases energy, making the resulting salt more stable than before.

Properties of Ionic Compounds When salts are dissolved in water, this breaks the ionic bonds and allows the individual ions to move freely in water. Only when salts are dissolved in water or melted are they able to conduct electricity (when they are called “electrolytes”).

Naming Ionic Compounds Ionic compounds that are composed of two elements are called Binary Compounds The names Binary compounds simply include the name of the cation element, and then the name of the anion element with –ide as a suffix Sodium Chloride: NaCl Barium Oxide: BaO Potassium Nitride: K 3 N Magnesium Iodide: MgI 2

Naming Ionic Compounds Ionic Compounds that include polyatomic ions (ions that are composed of more than one atom) will use specific ion names for the cation or the anion. These names are listed on the table on p Potassium Nitrate: KNO 3 Sodium Carbonate: Na 2 CO 3 Ammonium Chloride: NH 4 Cl Calcium Acetate: Ca(C 2 H 3 O 2 ) 2

Naming Ionic Compounds Transition Metals can have various charges (see pg. 219). Ionic Compounds that include Transition Metals will need to indicate the charge of the metal in the name (using a Roman Numeral). Chromium (III) Oxide: Cr 2 O 3 Iron (II) Chloride: FeCl 2 Tin (IV) Bromide: SnBr 4 Manganese (VII) Hydroxide: Mn(OH) 7