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 Need more convincing? Draw orbital diagram for F.

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+ Sometimes they will rearrange to have a pseudo-noble gas configuration (full outer shell, but not really) Copper usually has its electrons fully rearrange to form [Cu]4s13d10 instead of [Cu]4s23d9

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)

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

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

Nomenclature Naming Cation ALWAYS goes first. If transition metal—write roman numeral to specify oxidation state Anion ALWAYS goes second. Monoatomic—drop suffix and add –ide Polyatomic—use name of polyatomic ion

Practice Write the names for the following compounds: CaCl2 KF NH4Cl Na2SO4 NH4NO3 MnO MnO2

Practice Write the formulas for the following compounds: Platinum (IV) chloride Potassium bromide Magnesium sulfate Copper (II) chlorate Silver (I) dichromate Ammonium perbromate

Hydrides Hydrogen can gain or lose one e- depending on what it binds with… WHY? When bonding with metals, H gains an e- Since it is an anion, it gets the “-ide” suffix Examples: LiH, MgH2, NaH, etc.

Hydrates Contain water in crystalline lattice Can remove water without chemically altering substance Nomenclature is the same as ionic compounds, except take water molecules into account. How? Use prefixes to show number of water molecules

Practice Name the following compounds: NaCl∙2H2O MgSO4∙7H2O CuSO4∙5H2O CoCl2∙5H2O NiCl4∙3H2O

Practice Write the names for the following compounds: Iron (II) fluoride tetrahydrate Barium hydroxide octahydrate Lead (II) perchlorate pentahydrate Copper (II) acetate monohydrate Tin (II) chloride dihydrate