Ionic and Metallic Bonding

Objectives Be able to determine the number of valence electrons for an element. Be able to determine the charge on an ion by considering the number of valence electrons. Understand how/why ionic bonds can form.

Valence Electrons valence electrons (v/e): electrons in the highest occupied energy level (usually s and p) that are involved in bonding S: [Ne] 3s 2 3p 4 → 6 v/e Co: [Ar] 4s 2 3d 7 → 2 v/e K: [Ar] 4s 1 → 1 v/e Sn: [Kr] 5s 2 4d 10 5p 2 → 4 v/e Group number relates to number of v/e… 1 = 1 v/e 2 = 2 v/e 3 – 12 = 2 v/e 13 = 3 v/e 14 = 4 v/e etc. octet rule: atoms lose or gain electrons until they have stable noble gas electron configuration (an octet) ion: an electrically charged atom

Forming Cations and Anions metals lose v/e forming cations (+) non-metals gain v/e forming anions (–) Na: [Ne] 3s 1 Cl: [Ne] 3s 2 3p 5 [Ne] [Ne] 3s 2 3p 6 = [Ar] (11 p + and 10 e – ) (17 p + and 18 e – ) IMPORTANT: adding electrons → negative anion losing electrons → positive cation Mg: [Ne] 3s 2 Cl: [Ne] 3s 2 3p 5 Mg 2+ Cl – Na + Cl –

Ionic Compounds The “Yellow Sheet” shows common ions and charges. anions and cations attract, form ionic compounds net charge = zero chemical formula: shows ratio of atoms or ions in a compound ionic bond: very strong attraction between cations and anions Ca 2+ Cl – CaCl 2 Cl –

Objectives Be able to write the stock name of an ionic compound when given its chemical formula. Be familiar with polyatomic ions. Be able to write the chemical formula of an ionic compound when given its stock name.

Writing Chemical Formulas Write the formula (use “criss-cross” method): barium chloride aluminum oxide tin (IV) sulfide

Polyatomic Ions polyatomic ion: a group of atoms w/ electric charge SO 4 2– sulfate S O O O O 2– NO 3 – nitrate N O O O – NO 2 – nitrite N OO – NH 4 + ammonium NH H H H +

Writing Chemical Formulas Write the formula (use parentheses if more than one polyatomic ion is present): lithium carbonate aluminum nitrate lead (IV) sulfate ammonium sulfate

Writing Stock Names nomenclature: involves the names of things Write the correct stock name: SrF 2 FeCl 3 Cu(NO 3 ) 2 FeO

Objectives Be able to write the formula of an ionic compound when given its classical name. Be able to write the classical name of an ionic compound when given its chemical formula.

Classical Names The classical naming system uses Latin prefixes and endings (-ous or -ic). IonStock Classical Pb 2+ lead (II) plumbous Pb 4+ lead (IV) plumbic Cu + copper (I) cuprous Cu 2+ copper (II) cupric

Using Classical Names Write the formula: ferric sulfate = ? cuprous nitrate = ? Write the classical name: Pb(NO 3 ) 2 = ? Pb(NO 3 ) 4 = ?

Giant gypsum crystals (CaSO 4 2H 2 O) in Naica Mine, Mexico Ionic Compounds

Objectives Understand the concept of a crystalline lattice. Be able to identify a hydrate. Be able to identify and discuss the following properties of ionic compounds:  crystal structure  high melting point  solubility  conductivity  brittleness

Ionic Compounds NaCl CaCO 3 CuSO 4 ·5H 2 O CaF 2

crystalline lattice: 3-D repeating arrangement of ions shape depends on the ratio and sizes of ions Ionic Crystals

Properties of Ionic Compounds Combining Ions FormulaMelting Point Na + Cl - NaCl801 o C K + I - KI680 o C Al 3+ O 2- Al 2 O 3 ~2000 o C ionic bonds—opposite charges strongly attract solids with high melting points

Properties of Ionic Compounds contain 1+ or 1- ions? usually soluble (will dissolve) higher charges? usually insoluble (won’t dissolve) NaCl = soluble Al 2 O 3 = insoluble Na+ Cl– Al 3+ O 2–

Properties of Ionic Compounds +– – – – – +– – – – – +– – – – – +– – – – – +– – – – – +– – – – – +– Ionic solids DO NOT conduct electricity (ions cannot move)

Properties of Ionic Compounds + – – – – – + – – – – – – – – conduct electricity when molten or dissolved (ions are free to move) +–

Properties of Ionic Compounds Ionic compounds are brittle— like charges repel when a force rearranges the lattice. +– – – – – – – – – – +– – – – – +– – – – – – – – – – crystal “cleaves” force +– – – – –

Objectives Be able to explain how metals bond together (metallic bonding). Be able to identify and explain the properties of metals.

Metals The v/e in metals are delocalized, moving freely within a sea of electrons. metallic bond: attraction between delocalized electrons (-) and metal cations (+)

Metallic Properties cations are not rigidly held in place malleable: can be flattened ductile: can be made into wire

Metallic Strength # of v/e determines the strength and hardness of a metal Li, Na, K, Cu, Ag, Au (1 v/e): soft Ti (4 v/e): very hard and strong Mg, Cr, Fe, Ni (2-3 v/e): medium

Metallic Strength large radius tend to be softer: the larger distance between the nucleus and the v/e results in weak bonding PbHg

Metallic Properties Metals conduct electricity and heat—delocalized v/e are free to move

Alloys alloy: a mixture of different elements including one or more metals Strong because different-sized cations can’t slide around.

Common Alloys bronze: ~ 90% Cu, ~ 10% Sn steel: ~ 98% Fe, ~1% C (+ Cr, Mn, Ni, Mo, etc.) brass: Cu and Zn sterling silver: ~ 90% Ag, ~ 10% Cu