The Chemistry of Titanium

1. The Chemistry of Titanium 1d – Intermolecular Forces

2. Learning Intentions • To examine the effects of intermolecular forces on properties of a substance • To know how Van der Waals forces arise and their effect • To Know how permanent dipole/dipole interactions occur and their effect on properties • To know how hydrogen bonding arises and it’s importance for properties of some substances

3. ++ Monatomic elements He Noble gases have full outer electron shells They do not need to combine with other atoms. They are said to be monatomic. Group 0 are all gases and exist as individual atoms. However, the monatomic gases do form weak inter-atomic bonds at very low temperatures.

4. δ+ δ+ δ+ δ- δ- δ- ++ ++ Monatomic elements Sometimes the electrons can end up on one side of the atom, i.e. the electron cloud can wobble This means that one side of the atom is more negative than the other side. i.e. 2 ‘electric poles’ are formed, otherwise called a dipole. These charges are given the symbol δ ‘delta’ A temporary dipole is therefore formed. A dipole can induce other atoms to form dipoles, resulting in dipole –dipole attraction. Van der Waals forces

5. 180 166 160 140 120 100 80 60 40 20 0 121 4 87 27 Noble gases b.p.’s Helium Neon b.p / K Argon Krypton Xeon B.p.’s increase as the size of the atom increases This happens because the Van der Waals’ forces increases with increasing size of atoms.

6. A SMALL MOLECULE COVALENT SUBSTANCE

7. covalent bonds (strong)

8. intermolecular attractions (weak) what causes them? covalent bonds (strong)

9. intermolecular bonds (weak) = van der Waal’s forces MUCH WEAKER THAN covalent bonds (strong)

10. boiling point

11. boiling point WHY?

12. wee, light molecule weak attraction big, heavy molecule strong attraction lower boiling point higher boiling point

13. the higher the boiling point. the stronger the intermolecular attraction the heavier the molecule

14. Molecular Elements Fluorine atom Fluorine molecule F2 diatomic 9+ 9+ 9+ A covalent bond is formed when a pair of electrons are shared. The atoms in a covalent bond are held together by electrostatic forces between positively charged nuclei and negatively charged electrons. Strong covalent bond WeakVan der Vaals force Strong intra-molecular bonding and weak inter-molecular bonding exist in this diatomic molecule. F 2 m.p. -220o C or 53 K F F F F

15. 500 450 400 350 300 250 200 150 100 50 0 457 332 85 238 Halogens b.p.’s Fluorine b.p./ K Chlorine Bromine Iodine As the size of the halogen atom increases, so does the size of the van der waals’ forces between the halogen molecule.

16. Polar-Polar Attractions The differing electronegativities of different atoms in a molecule and the spatial arrangement of polar covalent bonds can cause a molecule to form a permanent dipole. No permanent dipole Symmetrical molecule Permanent dipole Asymmetrical molecule + - + - - - - - - 3 polar covalent C–Cl bonds and 1 polar covalent C-H bond in CHCl3 4 polar covalent C-Cl bonds in CCl4 tetrahedral shape NON-POLAR molecule POLAR molecule e.g. also H2O e.g. also CO2

17. Polar molecules and permanent dipoles Both propanone and butane have the same formula mass of 58 however, butane boils at – 1 oC while propanone boils at 56oC Propanone is a polar molecule as it has a permanent dipole, so has polar-polar attraction as well as Van der Waals’ forces between molecules. - b.p. 56 o C + Butane has no permanent dipoles, so only Van der Waals forces between molecules. So has a lower boiling point. b.p. -1 o C

18. F H + - Hydrogen Bonding Hydrogen bonding is a special type of dipole-dipole attraction in which hydrogen atom acts as a bridge between two very electronegative atoms. It is the strongest of the weak inter-molecular forces. A - H + B - The Hydrogen atom is in a straight line between A - and B - . The bond strength is stronger than other forms of permanent dipole-permanent dipole interaction but weaker than a covalent bond. A and B are electronegative atoms, such as F, O or N. Such atoms possess one or more lone pair of electrons. Proteins consist of long chain atoms containing polar >C=O and H-N< bonds. Hydrogen bonds help give proteins their shape.

19. Group 4 5 6 7

20. Group 4 5 6 7 1st row 2nd row 3rd row 4th row

21. The intermolecular attraction is much stronger than you would expect it to be. This extra strong attraction is given the name THE HYDROGEN BOND. But what causes it?

22. A A pure covalent bond

23. A A pure covalent bond d+ d- A B polar covalent bond

24. d+ d- H X A special type of polar covalent bond X = a highly electronegative element

25. covalent bonds Hd+ Xd- Hd+ Xd- Hd+ Xd- HYDROGEN BONDS d- d+ d- d+ d- d+ (HYDROGEN BONDING) X = a very electronegative atom

26. Covalent substances that have hydrogen bonding have higher melting points have higher boiling points often have harder crystals than you would otherwise expect.

27. WATER d- O H d+ d- H d+

28. O H H - Water + + Oxygen has 2 lone pairs of electrons which can form a hydrogen bonds with two hydrogen atoms. Each water molecule, in theory, could be surrounded by 4 hydrogen bonds Pond Skater Water has a high surface tension. The molecules on the surface have in effect, hydrogen bonds. This has the effect of pulling the surface molecules closer together. Ice Skater: Water has a its greatest density at a temperature of 4oC. When, as water cools further, the molecules start to move further apart, due to the hydrogen bonding, until a more open structure formed at its freezing point. So ice floats!!

29. sugars glucose

30. amino acids an amino acid

31. proteins

32. 3 billion DNA

34. haemoglobin

35. DNA