Chapter 10

1. Chapter 10

2. Intramolecular bonding-sharing electronsIntermolecular bonding- interactions between particles (atoms, molecules or ions)

3. condensed states of matter- liquids and solids***Changes in state are due to changes in intermolecular bonding (physical changes), not intramolecular bonding(chemical changes).

4. Intermolecular Forces(imf)

5. Dipole-dipole attraction-attraction of molecules having dipole moments for each other. (negative-positive)Polar molecules have dipole-dipole attractions for each other.

6. Dipole-dipole attractions are only about 1% as strong as covalent or ionic bonds. Molecules orient themselves to minimize repulsion and maximize attractions. Examples: HCl, H2S

7. Hydrogen bonding- unusually strong dipole-dipole attractions involving hydrogen atoms which are covalently bonded to a very electronegative element and a small, very electronegative atom (F,O,N) ( usually on an adjacent atom) with unshared electrons.

9. Two reasons for strength:1. small size of H atom allows closeness2. great polarity Substances with much H bonding have higher boiling points compared to similar substances. Ex. H2O, NH3, HF

10. While we normally think of hydrogen bonding only occurring between two different molecules, very large molecules such as proteins have different parts of the same Molecule forming hydrogen bonding within the same molecule. This helps to form the secondary structures of proteins.

11. London dispersion forces (LDFs) -relatively weak forces (usually) that exist between noble gas atoms and between nonpolar molecules. LDFs also exist in compounds that have dipole-dipole and/or hydrogen bonding. LDFs may be the most important force in large molecules of these types.

12. LDFs occur because of momentary electron imbalance (temporary dipole) which can induce the same in adjacent molecules.

14. At a given moment, there may be more electrons on one end of an atom or molecule than on the other end. This makes one end a little positive and the other end a little negative. This is a temporary dipole and can induce (cause) the same thing in an adjacent molecule (think chain reaction!). Polar molecules and even ions can cause an induced dipole in nearby nonpolar molecules.

15. This force is often very weak, thus the low freezing point of noble gases. The freezing point of noble gases increases as we go down the group because larger atoms have more electrons and an increased chance of temporary dipoles. We say that they are “more polarizeable” when they have more electrons.This causes London dispersion forces to increase down a group.

16. The boiling point of covalent hydrides increases with increasing molar mass(more electrons!) in Group 4. In other groups, the first hydride has a high boiling point because of hydrogen bonding.

18. Metallic bonding- Metallic elements have metal cations in a sea of mobile valence electrons.Ionic bonding- Cations and anions (usually metal and nonmetal) held together by electrostatic (Coulombic) attraction.

19. Covalent network bonding- This is extensive covalent bonding between atoms resulting in giant molecules. Group 4 elements often are involved (C, Si, SiO2, SiC)Metallic, ionic and covalent network bonding will be discussed further later on in this chapter.

20. General trends in strength of attractionLDFWeakest attractiondipole-dipoleH-bondingmetallic bondingionic bondingcovalent network solid Strongest attraction

21. Determine the type of intermolecular force each of the following substances have: • H2 • HCl • Fe • H2S • SiC • CO2

22. Rank these substances from lowest boiling point to highest boiling point. Justify your answers. NaCl, Ge, NH3, H2O, F2, SO2

23. Surface tension- resistance of a liquid to an increase in its surface area.Liquids with relatively large intermolecular forces have high surface tensions. ↑ imf = ↑ surface tensionPolar molecules have more surface tension than nonpolar molecules.

24. Capillary action- spontaneous rising of a polar liquid in a narrow tube.-caused by 2 forces:

25. cohesive forces: intermolecular forces among the liquid moleculesadhesive forces: forces between the liquid molecules and their container. The container must be made of polar material such as glass.

26. A concave meniscus forms because the water’s adhesive forces toward the glass are stronger than its cohesive forces.A nonpolar liquid (or liquid mercury) can produce a convex meniscus (cohesive > adhesive)

27. viscosity- resistance of a liquid to flowLiquids with large intermolecular forces tend to be highly viscous. Ex. glycerol (glycerine) ↑ imf = ↑ viscosityMore complex molecules are more viscous because they tangle up.

28. SOLIDS:amorphous solids- very disordered, usually long chain-like molecules twisted up like spaghetti. (plastics, asphalt, rubber)crystalline solids- highly regular arrangement of components

29. lattice- a 3-D system of points designating the centers of the components (atoms, ions or molecules)unit cell - smallest repeating unit of the lattice. (You don’t have to memorize these.)

31. coordination number- number of nearest neighbors surrounding a particle in a crystal For particles of the same size, the higher the coordination number, the greater is the number of particles packed into a given volume of the crystal.

32. X-ray diffraction- method of determining crystal structure.X-rays of a single wavelength are directed at a crystal and are scattered by it, producing a diffraction pattern which can be used to determine the crystal structure.

33. Types of crystalline solids

34. ionic solids (NaCl) -have ions at lattice points, held together byelectrostatic (Coulombic) forces.

35. Molecular solids (sucrose) - have molecules at lattice points, held together by LDF, dipole-dipole, &/or hydrogen bonding

36. metallic solids (gold)- have metal cations at lattice points, held together by metallic bonds

37. atomic solids (argon) - have noble gas atoms at lattice points, held together by LDF

38. covalent network solid(diamond and silicon compounds) (essentially one giant molecule)- covalently bonded, have an atom at each lattice point, held together by covalent bonds

39. The properties of a solid depend on the nature of the forces that hold the solid together. Diamond has very strong forces.

40. Metallic crystals- have nondirectional covalent bonding-spherical atoms packed together and bonded to each other equally-called metallic bonding

41. Bonding in Metals-strong and nondirectional-atoms are difficult to separate, but easy to move

42. Two models are used to describe metallic bonding. They are:

43. Electron sea model - This is the simplest model. The metal cations are in a sea of valence electrons. The mobile electrons can conduct heat and electricity. The cations can be easily moved around .

45. Band model (MO model) -This is a more detailed model. The electrons are assumed to travel around the metal crystal in molecular orbitals formed from the valence atomic orbitals of the metal ions. The MOs that result are very closely spaced in energy levels, thus they form a continuous band. Some MOs are empty. Mobile electrons are excited into these empty MOs. The electrons are free to move throughout the metal crystal.

47. Metal alloy - substance that contains a mixture of elements and has metallic properties

48. 2 types:substitutional alloy - some of the host metal atoms are replaced by other metal atoms of similar size. Ex. brass, sterling silver, pewter

49. interstitial alloy -holes in closest packed metal structure are filled by small atoms. The density of an interstitial alloy is higher than a substitutional alloyEx. steel (carbon in iron)

50. Network solids -atomic solids with strong directional covalent bonds-brittle and don’t conduct heat or electricity-Ex. C and Si-strongest type of bonding