Ionic and Metallic Bonding Chapter 7 Chemistry 2

Ions 7.1

Valence Electrons 7.1 the e- in the highest occupied energy level Elements are alike b/c same # of valence e- Look at group # to find He = exception Group 1A = 1 Group 2A = 2 Group 3A = 3 Usually used in bonding Electron Dot Configuration – diagram that shows valence e-

The Octet Rule 7.1 When forming compounds, elements try to achieve an e- configuration like noble gases Set of 8 Metallic elements tend to lose e- Nonmetallic tend to gain or share e-

Formation of Cations 7.1 + charge ion Loses valence e- Name the same as Neutral Element (Na) = Sodium  (Na+) = Sodium ion Chemical differences when changes Na loses 1 e- so now has e- configuration of Neon Mg (group 2A) loses 2e- = Mg2+ = now e- conf of Neon Ions with more than 3 charge can happen but are not likely

Formation of Anions 7.1 Negative charge Gain e- Name not the same as the neutral element Ends in –ide (Cl) Chlorine = (Cl-) Chloride ion Cl gains 1 e- to have same e- configuration as Ar Halide Ions – ions produced when halogens gain e- Halogens = 7 valence e-  gain 1 e- = octete rule

Ionic Bonds and Ionic Compounds 7.2

Formation of Ionic Compounds 7.2 Cations + anions = ionic compounds Neutral Ex: table salt = NaCla Transfer of e- Attracted to one another b/c of opposite charge = ionic bonds = electrostatic force Equal number of cations and anions Chemical formula – shows kinds and umbers of atoms in smallest representative units Ex: NaCl Formula Unit – lowest whole-number ratio of ions in an ionic compound NaCl = 1:1 MgCl2 = 1:2 AlBr3 = 1:3 Page 196 – Practice Problems 12 - 13

Properties of Ionic Compounds 7.2 Most solid at room temp Some form crystals = repeating 3-D pattern NaCl = each Na surrounded by 6 Cl ions Each Cl surrounded by 6 Na and so on = very strong and stable compounds High Melting Points Coordination number - # of ions of opposite charge that surround the ion in a crystal NaCl = 6 Conduct electric current when melted or dissolved in water Cations(+) migrate to cathode (-) Anions (-) migrate to anode (+)

Bonding in Metals 7.3

Metallic Bonds and Metallic Properties 7.3 Metals = closely packed cations (+) Valence e- are mobile and drift from one part of metal to another = sea of electrons Metallic Bonds – attraction of free-floating valence e- for the positively charged metal ions Good conductors b/c electrons can flow freely in them Ductile (drawn into wire) Malleable e- slide past one another

Crystalline Structure of Metals 7.3 Metals are crystalline Atoms arranged in very compact and orderly pattern Patterns Body Centered Cubic Every atom, besides those at surface have 8 neighbors Ex: Na, K, Fe, Cr, W Face-Centered Cubic 12 neighbors Ex: Cu, Ag, Au, Al, Pb Hexagonal Close-Packed Hexagonal shape Mg, Zn, Cd

Alloys 7.3 Mixtures composed of 2 or more elements (1 which is a metal) Ex: Brass – copper and zinc Properties are normally better Sterling Silver (silver and copper) Harder and more durable than silver Bronze (7 parts copper, 1 part tin) Harder and more easily cast Steel Iron, Carbon, Boron, Chromium, Manganese, Molybdenum, nickel, tungsten, and vanadium

Technology and Society Building With Alloys Taller, lighter, buildings b/c of steel Support large, open interior w/o supporting walls