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2 types of Intermolecular forces 1. Van der Waal’s forces (attraction between partial + charge on one molecule & partial - charge on another molecule)

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Presentation on theme: "2 types of Intermolecular forces 1. Van der Waal’s forces (attraction between partial + charge on one molecule & partial - charge on another molecule)"— Presentation transcript:

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2 2 types of Intermolecular forces 1. Van der Waal’s forces (attraction between partial + charge on one molecule & partial - charge on another molecule) 2. Hydrogen bonding >

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8 hydrogen bond Formation of hydrogen bonds between HF molecules. Electrostatic attraction exists between partial positive charge of H atom and the lone pair electrons of F atom of another HF.

9 Formation of hydrogen bonds between H 2 O molecules. hydrogen bond Electrostatic attraction exists between partial positive charge of H atom and the lone pair electrons of O atom of another H 2 O.

10 Formation of hydrogen bonds between NH 3 molecules. hydrogen bond Electrostatic attraction exists between partial positive charge of H atom and the lone pair electrons of N atom of another NH 3.

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12 Class practice 27.3 Identify the hydrogen atoms of the following species that are capable of forming hydrogen bonding with water molecules. (a) CH 3 OH (b) (c) Hydrogen bond -- between H atom (bonded to F,O,N) and lone pair of electron (on F,O,N)

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14 P. 13 / 2 (a) CH 3 OH (b) A27.3 (c) (b)

15 Boiling point (°C) Period H2OH2O H2SH2S H 2 Se H 2 Te HF HCl HBr HI NH 3 PH 3 AsH 3 SbH 3 CH 4 SiH 4 GeH 4 SnH 4

16 Molecular size of hydride molecules increases down a group  the van der Waal’s forces between molecules increases down a group Boiling point (°C) Period H2OH2O H2SH2S H 2 Se H 2 Te HF HCl HBr HI NH 3 PH 3 AsH 3 SbH 3 CH 4 SiH 4 GeH 4 SnH 4

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19 High electronegativities of F, O and N. Besides van der Waal’s forces, there are hydrogen bonds between molecules of NH 3, H 2 O and HF. However, there is weak van der Waal’s forces between other molecules only. Hydrogen bond is stronger than van der Waal’s forces A lot more energy is needed to break hydrogen bonds between molecules  The melting and boiling pt of NH 3, H 2 O and HF are much higher than expected.

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24 Molecular size of hydride molecules increases down a group  the VDW forces between molecules increases down a group

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26 Besides van der Waal’s forces, there are hydrogen bonds between H 2 O molecules. However, In H 2 S, H 2 Se, H 2 Te, there are weak van der Waal’s forces between molecules only. Hydrogen bond is stronger than van der Waal’s forces A lot more energy is needed to break hydrogen bonds between molecules  The melting and boiling pt of water are much higher than expected.

27 Fig Droplets of water are caused by high surface tension that pulls water molecules into a sphere. 2. Surface tension

28 There are extensive hydrogen bonds between water molecules. The surface tension of water is much higher than that of most other common liquids. hydrogen bond

29 LiquidRelative surface tension C 6 H ( no of H bonding per molecule= 0) CH 3 OH(methanol)22.6 ( no of H bonding per molecule= 1) CH 3 CH 2 OH22.8 ( no of H bonding per molecule= 1) H2OH2O72.3 ( no of H bonding per molecule= 2) hydrogen bond

30 3. Viscosity The resistance of a liquid to flow. The higher the viscosity of a liquid, the more slowly it flows. Viscosity

31 Strong intermolecular forces hold molecules together and do not allow them to move past one another easily. Liquid water molecules Benzene molecules Hydrogen bonds Weak intermolecular forces held by

32 LiquidRelative viscosity Benzene1 Water15 Table 27.4 Relative viscosities of some liquids at 25°C. Water has high melting and boiling points, high surface tension and is more viscous than benzene. Experiment 27.1

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34 P. 33 / 15 The oxygen atom of each water molecule forms hydrogen bonds with two hydrogen atoms of nearby water molecules. Structure and bonding of ice a water molecule hydrogen bond hydrogen bond hydrogen atom oxygen atom

35 P. 34 / 15 The two hydrogen atoms of each water molecule also form hydrogen bonds with oxygen atoms of nearby water molecules. hydrogen bond hydrogen bond hydrogen atom oxygen atom

36 P. 35 / The central oxygen atom of each water molecule has a tetrahedral arrangement of two lone pairs (forming hydrogen bonds) and two bond pairs. Fig A water molecule can form hydrogen bonds with four other water molecules.

37 P. 36 / 15 In solid ice, the tetrahedral arrangement repeats over and over again, resulting in a regular open network structure of water molecules.

38 P. 37 / 15 hydrogen bond empty space a water molecule Fig The structure of ice.

39 P. 38 / 15 Fig The oxygen atoms in the structure of ice are arranged in a hexagonal shape.

40 P. 39 / 15 Fig The hexagonal symmetry of a snowflake reflects the structure of ice.

41 P. 40 / 15 Explanation In ice, water molecules are arranged in an orderly manner in an open network structure because of extensive hydrogen bonding. Open network structure!

42 P. 41 / 15 liquid water In this open structure, water molecules are further apart than they are in liquid water. melts open structure collapses water molecules tend to pack more closely together Think about ice

43 P. 42 / 15 Ice presence of extensive hydrogen bonding between water molecules regular open network structure low density relatively high melting point High viscosity

44 Ethanol CH 3 CH 2 OH hydrogen bond The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another ethanol molecule. The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another water molecule.

45 Ethanol CH 3 CH 2 OH hydrogen bond The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another ethanol molecule. The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another water molecule. High Solubility in water

46 Ethanol CH 3 CH 2 OH hydrogen bond The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another ethanol molecule. The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another water molecule. High boiling point

47 Ethanol CH 3 CH 2 OH hydrogen bond The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another ethanol molecule. The hydrogen atom of an ethanol molecule can form a hydrogen bond with the oxygen atom of another water molecule. High viscosity

48 Ethanol is completely miscible with water, and has high boiling point. It is as viscous as water.

49 Ethanoic acid CH 3 COOH

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51 Fig There are hydrogen bonds between the base pairs on the nucleic acid chains. hydrogen bonds

52 Effect of hydrogen bonding on DNA Hydrogen bonds between specific base pairs hold two nucleic acid chains of a DNA molecule together. The presence of hydrogen bonds helps maintain the double helical shape of the molecules.

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54 b.p / density/ viscosity of molecules Affected by Strength of van der Waal’s forcesPresence and no. of hydrogen bonds Molecular size Shape Polarity of molecules Affected by (1. Presence of lone pair electrons on F,O,N on one molecule 2. Presence of H attached to F,O,N on another molecule) No. of hydrogen bonds per molecule = minimum no. of lone pair electrons on F,O,N / no, of H attached to F,O,N

55 Molecular crystals Crystals having an ordered arrangement of molecules are called molecular crystals. table sugar ice Examples: ice, table sugar and iodine

56 Fig The crystal structure of iodine. Iodine molecules are arranged orderly in iodine crystal. These molecules are closely packed together, but they are still separate molecules. These molecules are held together by relatively weak intermolecular forces.

57 P. 56 / 15 The oxygen atom of each water molecule forms hydrogen bonds with two hydrogen atoms of nearby water molecules. Structure and bonding of ice a water molecule hydrogen bond hydrogen bond hydrogen atom oxygen atom

58 P. 57 / The central oxygen atom of each water molecule has a tetrahedral arrangement of two lone pairs (forming hydrogen bonds) and two bond pairs. Fig A water molecule can form hydrogen bonds with four other water molecules.

59 P. 58 / 15 In solid ice, the tetrahedral arrangement repeats over and over again, resulting in a regular open network structure of water molecules. Learning tip

60 P. 59 / 15 hydrogen bond empty space a water molecule Fig The structure of ice. ice (ball) ice (ball)

61 P. 60 / 15 Explanation In ice, water molecules are arranged in an orderly manner in an open network structure because of extensive hydrogen bonding. Open network structure!

62 P. 61 / 15 liquid water In this open structure, water molecules are further apart than they are in liquid water. melts open structure collapses water molecules tend to pack more closely together Think about ice

63 P. 62 / Melting point Water has a high melting temperature compared with substances of similar molecular masses. SubstanceRelative molecular massMelting point (°C) Nitrogen18 − 210 Ammonia17 − 78 Water180

64 P. 63 / 15 Ice presence of extensive hydrogen bonding between water molecules regular open network structure low density relatively high melting point

65 P. 64 / 13 Structure and bonding of fullerenes Fullerenes are molecules composed entirely of carbon atoms, in the form of hollow spheres or hollow tubes.

66 P. 65 / 13 Buckminsterfullerene (or buckyball) The first fullerene discovered was buckminsterfullerene. Fig (a) The structure of buckminsterfullerene. (b) A soccer ball.

67 P. 66 / 13 Each carbon atom is connected to three other carbon atoms by one double covalent bond and two single covalent bonds. The atoms are arranged in a pattern of 20 hexagons and 12 pentagons on the surface of the sphere.

68 P. 67 / 13 Do you know? Other related molecules composed of only carbon atoms were also discovered. Class practice 28.2 C 28 C 32 C 50 C 70 Fig Some of the more stable members of the fullerene family. (a) C 28 (b) C 32 (c) C 50 (d) C 70

69 P. 68 / 13 GraphiteGraphite DiamondDiamond insoluble in all liquid solventsinsoluble solvents C 60 dissolves in organic in organicsolventdissolves solvent 1. Solubility

70 P. 69 / 13 buckminsterfullerene (C 60 ) is an electrical insulator. 2. Electrical conductivity SubstanceElectrical conductivity Graphite√ (with delocalized e-) DiamondX C 60 X (simple molecular structure, No ions, no delocalized electrons

71 P. 70 / 13 SubstanceMelting point (°C) Graphite3730 (Giant covalent structure) Diamond3550(Giant covalent structure) C (Simple molecular structure) C 60 molecules are held together by weak van der Waals’ forces. 1. Melting point

72 P. 71 / 13 buckminsterfullerene molecule (C 60 ) Buckminsterfullerenes are relatively strong and hard compared with most other molecular solids. Fig The C 60 molecules are packed closely together in solid state. 3. Strength and hardness


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