Ionic Bonding = Ca 3 P 2 Formula Unit chemical formula - shows kinds and numbers of atoms in smallest representative particle of substance. Formula Unit - smallest representative particle in ionic cmpd Ionic bonds 6:28
1. Crystalline solids - regular repeating arrangement of ions in the solid: Fig. 7.9, page 197 Ions strongly bonded Rigid structure 2. High melting points Coordination number- # of ions of opposite charge surrounding it Chemistry of salt 6:23
- Page 198 Coordination Numbers: Both the sodium and chlorine have 6 Maximizes contact btwn opp charges Both the cesium and chlorine have 8 Each titanium has 6, and each oxygen has 3 NaCl CsCl TiO 2
3. Melted ionic cmpds conduct Crystal structure breaks down ions free to move (molten or aqueous)
OBJECTIVES: Model the valence electrons of metal atoms.
OBJECTIVES: Describe the arrangement of atoms in a metal.
OBJECTIVES: Explain the importance of alloys.
How metal atoms are held together in the solid. Metals hold on to their valence e-’s weakly. positive ions (cations) floating in sea of e-’s (Fig. 7.12, p.201)
Strong Repulsion breaks crystal apart, b/c similar ions next to each other. + - + - + - +- +-+- + - +- Force
Metals are crystalline Metals w/ 1 type of atom simplest crystalline solid Compact & orderly patterns Fig. 7.14 p.202: 1. Body-centered cubic: Fig. 7.14 p.202: every atom has 8 neighbors (except atoms on surface) Na, K, Fe, Cr, W
2. Face-centered cubic: every atom has 12 neighbors Cu, Ag, Au, Al, Pb
3. Hexagonal close-packed 12 neighbors different pattern due to hexagonal Mg, Zn, Cd
We use metals every day, few pure metals Alloys made by melting a mixture of ingredients, then cooling Brass: alloy of Cu and Zn Bronze: Cu and Sn
Properties superior to pure element Sterling Ag (92.5% Ag, 7.5% Cu) harder than pure Ag Soft enough for jewelry & tableware Steels important corrosion resistant, ductility, hardness, toughness, cost efficient
Table 7.3, p.203 – lists alloys Types: a) substitutional alloy- atoms in components are about same size b) interstitial alloy- atomic sizes differ; smaller atoms fit in spaces btwn larger “Amalgam”- dental fillings, contains 50%Hg, 22%Ag, 14%Sn, 8%Cu