Ionic compounds

What is a bond? A mutual electrical attraction between the nuclei and valence electrons of different atoms that binds them together. Can be formed by atoms gaining, losing, or sharing electrons. Why do atoms form chemical bonds? To become more stable (lower potential energy) ONLY valence electrons are used for bonding.

Ionic bonds Atoms lose or gain electrons to satisfy octet (become more stable) Form two kinds of ions—atom that has an electrical charge. Cations—positively charged atoms. Anions—negatively charged atoms

Periodic trends associated with ionic bonding Ionization energy—energy required to remove an electron from the outer shell of an atom. Electron affinity—the change in energy when an electron is added to the outer shell. For bonding—High IE, high EA = less likely to give electrons = anion Low IE, low EA = more likely to give electrons = cation

Formation of Cations Atoms that lose electrons: Examples: Metals Low IE - does not require a ton of energy to take an e- away Low EA - does not readily accept other e- into outer shell. Examples: Metals Li, Na, K, Be, Mg, Ca, etc. Draw orbital diagrams for the following: Li Mg Al

Transition Metals Form cations with different oxidation states (depends on what it’s bound to) Titanium: [Ar]4s23d2 Can lose two electrons for Ti2+ or four electrons for Ti4+

Formation of Anions Atoms that gain electrons: High IE—requires a ton of energy to take an e- away High EA-readily accepts other e- into outer shell. Examples: Halogens and nonmetals F, N, O, Cl, etc. Draw orbital diagrams of the valence shells of the following: F S Br

Write the oxidation states for the following elements Mg Li P Ca Ba I K O S Cl N F

Ionic Bonds Held together by electrostatic force Electrostatic force—force of attraction between positively and negatively charged particles

Crystal lattice What is it? a 3 dimensional geometric arrangement of particles where + and – ions surround each other the ions are packed into a regular repeating pattern that balances the forces of attraction and repulsion between the atoms

Crystal lattice Na Cl - In a solid state, ionic compounds are non-conductors, ions must be free to move for a current to pass through it - In a liquid state (molten) or when dissolved in water they are good conductors (ions are free to move)

Amorphous—particles are arranged randomly throughout the solid Crystalline—particles pack in an organized fashion Amorphous Crystalline

Amorphous Crystalline

Lattice energy The energy released when 1 mol of an ionic compound is formed from gaseous ions. Endothermic—energy has to be absorbed for the rxn to happen Surroundings are colder Exothermic—energy is released (Ex: -436 kJ/mol) Surroundings feel warmer since energy is given off Which is more stable?

Formation of ionic compounds is almost ALWAYS exothermic Why Formation of ionic compounds is almost ALWAYS exothermic Why??? More stable with lower potential energy

Formulas Formula unit - represents the most simple ratio of the ions in an ionic compound The total number of e-‘s gained by the nonmetal must equal the number lost by the metal atoms Oxidation states - give insight into how the atom will bond Used to determine the formula for a compound

Polyatomic Ions Two or more atoms that together carry a charge the charge given applies to the entire group of atoms acts like an individual ion if more than one polyatomic ion is required, use ( ) then subscript Ca(NO3)2 Example: Nitrate, NO3-1 and Ammonium, NH4+

Nomenclature What is it?? Rules for ionic nomenclature The naming and writing of formulas for chemical compounds. Rules for ionic nomenclature 1.) Cation is ALWAYS written first. 2.) Anion is ALWAYS written second. 3.) Use subscripts to cancel out charges 4.) Overall charge of the compound formed is always ZERO

Write the formulas for a compound formed by the following elements. Practice Write the formulas for a compound formed by the following elements. K and Cl Mg and Br Li and O

Rules for ionic nomenclature Write the name of the cation 1st using the elements name Write the root word of the anion 2nd plus change the suffix to “ide” Transition metals can have more than one ox. # Write the elemental name then give ox. # as roman numeral in parenthesis. Ex: iron (III) oxide NEVER change the name of a polyatomic ion

Write the name of the following compounds: Practice Write the name of the following compounds: MgCl2 CaCO3 MgSO4 KCN NaOH

Write the formulas for the following compounds: Practice Write the formulas for the following compounds: Magnesium Bromide Sodium Nitrate Calcium Carbonate Palladium (II) Chloride