1. Welcome to Chem 2010 General chemistry (I) For third Level Chemistry, Biology and Physics Departments Chapter 8 1

2. Chapter 8: STATES OF MATTER AND ENTERMOLECULARE FORCES 2

3. Matter is anything that has mass and occupies space. Mass is a measure of the quantity of matter in a sample of any material. Matter STATES OF MATTER solidliquid gas 3

4. In the solid state, substances are 1- rigid and have definite shapes. 2- Volumes of solids do not vary much with changes in temperature (Expansion on Heating slight) 3- Volumes of solids do not vary much with changes in pressure (slight compressability). 4- Intermolecular spaces are smoll 5- Attractive force between atoms is very big. 4

5. 6- Attractive force between atoms is middle. 5- Intermolecular spaces are middle. 4- Liquids are very hard to compress. (slight compressability) 3- Expansion on Heating slight 2- A liquid flows and assumes the shape of its container up to the volume of the liquid. 1- the individual particles are confined to a given volume. In the liquid state, 5

6. In the gas state, 1- Gases are much less dense than liquids and solids. 2- They occupy all parts of any vessel in which they are confined. 3- Gases are capable of infinite expansion 4- Gases are compressed easily. 5- Intermolecular spaces are big 6- Attractive force between atoms is very small 6

7. LIQUID SOLID GAS Tightly packed, in a regular pattern Vibrate, but do not move from place to place Close together with no regular arrangement. Vibrate, move about, and slide past each other Well separated with no regular arrangement. Vibrate and move freely at high speeds States of Matter 7 Lecture7: state of matter & intermolecular forces 7

8. PHASE CHANGES Sublimation is the conversion of a solid directly to a gas without passing through the liquid state; the reverse of that process is called deposition. The changes shown in blue are endothermic (absorb heat); those shown in red are exothermic (release heat). relatively fixed in position, but those in the liquid and gas can flow around each other. Physical changes that occur among the three states of matter. 8

9. INTERMOLECULAR FORCES

10. Why is water usually aliquid and not a gas? Why does liquid water boilat such a high temperature for such a small molecule? Why does ice float on water? Why do snowflakes have 6sides? Why is I2 a solid whereasCl2 is a gas? Why are NaCl crystals little? WHY? 10

11. The answers have to do with … INTERMOLECULAR FORCES

12. 12 Intermolecular Forces There are 2 types of attraction forces in matter Intramolecular bonds(chemical bond) "attraction between atoms inside the molecules” 1- ionic bond 2- polar covalent bond 3- non polar covalent bond intermolecular forces( physical bond) "attraction between molecules” ?

13. INTRAmolecularforces  —the forces holding atoms together to form molecules. INTERmolecular forces  Forces between molecules, between ions, or between molecules and ions. 13

14. Intermolecular Forces Intramolecular forces determine such molecular properties as molecular geometries and dipole moments Intermolecular forces determine the macroscopic physical properties of liquids and solids Intermolecular Forces 14

15. 15 1- Ion–Ion Interactions INTERMOLECULAR ATTRACTIONS AND PHASE CHANGES 2- Dipole– Dipole Interactions 3- Hydrogen Bonding 4- Dispersion Forces Intermolecular Forces Types of intermolecular forces( physical bond) (between 2 non-polar molecules) (between 2 “special” polar molecules) (between 2 polar molecules) (between ions in an ionic compound)

16. 16 Intermolecular Forces 1- Ion-Ion interaction The attractive force between ions in an ionic compound. Ion – Ion interaction exist in ionic compounds such as NaCl, CaBr 2, and K 2 SO 4

17. Ion-Ion Forces for comparison of magnitude  Na+—Cl- in salt  These are the strongest forces.  Lead to solids with high melting temperatures.  NaCl, mp = 800 C0  MgO, mp = 2800 Co 17

18. 2-Dipole-Dipole Forces Such forces bind molecules having permanent dipoles to one another. 18

19. 2- Dipole-Dipole Forces Attractive forces between polar covalent molecules Intermolecular Forces The positive end of the polar compound is attracted to the negative end of a nearby molecule. dipole–dipole interactions become less important as temperature increases. 19

20. 20 Intermolecular Forces The hydrogen bond is a special case of dipole-dipole interaction. occurs between hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. 3- Hydrogen bonding

21. 21 Intermolecular Forces 4- Dispersion (London) Forces Non-polar molecules ( as hydrocarbons) do not have dipoles like polar molecules. How, then, can non-polar compounds form solids or liquids? 1- Because electrons are moving around the nucleus, sometimes, the charge around the nucleus is not symmetrical and a temporary dipole occur. 2- The temporary dipole forms in one atom or molecule, induce a dipole in the neighboring atoms.

22. Intermolecular Forces 22

23. 23 Intermolecular Forces The larger the molecule, the greater it’s Dispersion Forces are. Dispersion (London) forces are present between all types of molecules in condensed phases

24. Because the boiling point of alkanes increase with the length of the carbon chain. i.e. Long-chain alkanes have larger dispersion forces than short-chains. Decane C 10 H 22 has greater boiling point than C 5 H 12 Why? Intermolecular Forces 24

25. 25 Intermolecular Forces Dispersion forces usually increase with molar mass.

26. To detect the type of intermolecular forces in a compound, It is important to be able to tell whether a substance is ionic, nonpolar covalent, or polar covalent. Compound in Question Ionic or Molecular? ionic has Ion –ion interactions Molecular Polar or NonPolar? Polar Non-Polar Has Dipole-dipole force Has dispersion forces Can it hydrogen bond ? hydrogen bonding will be formed if compound has H and O, F, or N 26

27. 27 Intermolecular Forces 920 kJ is required to break the covalent bonds between H and O in one mole of water. Intermolecular forces ( physical bonds) are weaker than intramolecular forces( chemical bonds), Example Whiles only 40.7 kJ is required to convert one mole of liquid water into steam at 100°C.

28. S O O What type(s) of intermolecular forces exist between each of the following molecules? HBr 1- HBr is a polar molecule: dipole-dipole forces. 2- There are also dispersion forces between HBr molecules. CH 4 CH 4 is nonpolar: only dispersion forces. SO 2 1- SO 2 is a polar molecule: dipole-dipole forces. 2- There are also dispersion forces between SO 2 molecules. 28

29. 29 Properties of the liquid state We will briefly discuss the evaporation process and vapor pressure Capillary action Surface tension viscosity Evaporation Vapor pressure

30. 30 Vaporization Vaporization ( evaporation), is the process by which molecules on the surface of a liquid break away and go into the gas phase. To break away, the molecules must have enough kinetic energy to overcome the intermolecular forces. The rate of vaporization increases as temperature increases.

31. 31 “Amount of heat needed to change 1 gram of liquid to gas at its boiling point.” Boiling (Condensing) Point of Water = 100°C Heat of Vaporization (water) = 2260 J/g Heat of vaporization

32. 32 Dispersion forces generally increase with increasing molecular size, so substances composed of larger molecules have lower vapor pressures. The relation between the intermolecular forces and vapor pressure of a liquid The relation between the intermolecular forces and vapor pressure of a liquid The very strong hydrogen bonding in water is the reason for its unusually low vapor pressure.

33. 33 1- Detect the intermolecular forces that are present in each of the following compounds. (a) CH 3 OH (methyl alcohol) (b) NH 3 ( c ) HCl (d) C 6 H 14 (hexane) (e) H 2 O Exercise (g ) NaCl (h) BrF (f ) SO 2 A, b, e Hydrogen bonding + dispersion force d Dispersion force g Ion –ion interaction c, f, h Dipole- dipole interaction + dispersion force

34. 34 Explain why? (a) CH 3 OH boils at 65°C while CH 4 boils at -161°C. (b) Boiling point of C 5 H 12 is greater than that of C 2 H 6 ( c ) at definite temperature, vapor pressure of C 5 H 12 is lower that vapor pressure C 2 H 6 Exercise