Ionic and covalent Bonding and Properties of Solids

1. Ionic and covalent Bonding and Properties of Solids

2. Chemical Bonding sites The Orbitron:a gallery of atomic orbitals and molecular orbitals on the WWWhttp://www.shef.ac.uk/chemistry/orbitron/Excellent sites for shapes of molecules:http://www.chemmybear.com/shapes.html

3. Electron Dot Structures • All chemistry textbooks have a chart like this

4. Loss & Gain of electron(s) • Atoms are stable when they have an “octet” or Nobel gas configuration. • Atoms form ions through the gain or loss of electrons • Opposites attract and ionic compounds are formed

5. Formation of an Ionic Compound Using Electron Configurations • Sodium looses 1 electron and chlorine gains one electron to form an “octet” or Nobel gas configuration.

6. Electron Dot Formula of an Ionic Compound • Magnesium atoms lose 2 electrons to become stable • Nitrogen atoms gain 3 electrons to become stable • 3 Mg ions (+6) and 2 nitrogen atoms (-6) = 0 net charge;)

7. Properties of Ionic Compounds • Usually solid crystals @ room temp (types of crystal structure & coordination number) • Generally have high melting points • Can conduct electricity when melted or dissolved in water • Formula represents number of ions in a representative unit

8. Metallic Bonds • Metals are made up of closely packed cations rather than neutral atoms • Valence electrons are mobile (sea of electrons) • Metallic bonds consist of attractions of the free-floating valence electrons for the positively charged metal ions

9. Metallic Properties & Structures: • Good conductors of electricity • Can be drawn into wires (ductile) • Can be hammered or forced into shapes (malleable) • Arranged in very compact & orderly patterns • Alloys are a mixture of 2 or more elements, at least one of which is a metal

10. Single Covalent Bonds • Nitrogen needs 3 additional electrons to satisfy its octet but cannot remove them from hydrogen so they share electrons • Carbon needs 4 additional electrons to satisfy its octet but cannot remove them from hydrogen so they share electrons

11. Double Bonds • Oxygen cannot remove 2 electrons from another oxygen so they share 2 pairs (double bond) • Nitrogen cannot remove 3 electrons from another nitrogen so they share 3 pairs(double bond)

12. Coordinate Covalent Bonds • Coordinate covalent bond is formed when one atom donates an unshared electron pair to the bond. In this case oxygen donates on of its unshared pairs. • This is seen frequently in polyatomic ions!

13. VSEPR (valence shell electron pair repulsion theory) Electron pairs repeland molecules adjust their shapes so that their valence shell electrons are as far apart as possible

14. VSEPR continued

15. Molecular Compounds - 2 or 3 pairs of electrons around central atom Each “-” between atoms represents a shared pair of electrons

16. Octets - 4 pairs of electrons around central atom

17. Expanded Octets - 5 pairs

18. Expanded Octets - 6 pairs

19. Covalent (polar/nonpolar) or Ionic? Bond type determined by difference in electronegativity and molecular shape

20. Intermolecular Forcesattractions between molecules

21. Intermolecular Forces -attractions between molecules • Hydrogen bonds • Strongest intermolecular attraction • Occurs between the hydrogen atom of one molecule and a very electronegative (O, N, or F) atom in another molecule

22. Dipole moment u = 1.85 D Polarizability α = 1.48 x 10-24 cm3 δ- δ+

23. Solids Crystalline: orderly array Amorphous: random jumble

24. (all crystalline!) • Forces in solids: • Metallic: metallic bonds (metal ions in electron sea) • Ionic: electrostatic (anions and cations) • Network: covalent bonds • Molecular: London, dipole-dipole, hydrogen bonds

25. Numerous Unit Cells for Different Crystal Structures Unit cell: the smallest representation of a crystal that reproduces the whole crystal. (do not memorize this table!)

26. Layered structure of metallic solids (A and B are same type of atom)

27. Hexagonal close-packed metallic structure: Coordination number is 12 (number of nearest neighbors for each atom; 6 in same plane and 3 above and 3 below) (the other major structure is cubic close-packed; Al, Cu, Ag, Au) Mg, Zn

28. Bravais Lattices for Unit Cells of Metallic Solids* * don’t memorize these! No way!

29. A metal crystallizes in a cubic cell structure with an edge length of 3.308 A. Its density is 4.401 g/cm3. What is the element? edge

30. Structures of Ionic Solids NaCl unit cell (coordination # 6) Note: anions and cations are different sizes!

31. Billions of “unit cells” to create NaCl crystals

32. Molecular Solids • Sucrose • Ice Ice H O

33. Network Solids: Strong covalent bonds Graphite: hexagonal rings of sp2 hybridized carbons Others: Diamond, ceramics

34. Properties of Solids: Density Conductivity “Luster”

35. Malleability

36. Alloys: Mixtures of Two or More Metals

37. Alloys Substitutional Interstitial Harder and stronger, but less conductive

38. Catalytic Converter Pt, Rh 2 NO  N2 + O2 2 CO + O2  2 CO2 hydrocarbons + O2  CO2 + H2O Pt, Pd Pt, Pd emissions honeycomb ceramic coated with Pt, Pd, Rh

39. Semi-Conductor • Si doped with P or As (electron rich) • Si doped with B or Ga (electron poor) No current across junction with this set-up

40. PROPERTIES OF MATTER