The kinetic Molecular Theory of Liquids and solids

Transcription

1 The kinetic Molecular Theory of Liquids and solids

2 States of Matter The fundamental difference between states of matter is the distance between particles Pearson Education, Inc. Intermolecular Forces

3 Characteristics properties of gases, liquids,and solids Definite volume Definite shape density compressibility Molecular motion gas liquid solid no no low high free yes no high slight slide yes yes high no vibrate

4 . States of matter solid Liquid Gas. the various states of matter can be understood by examining attractive forces between molecules Intermolecular Forces

5 Intermolecular Forces Attractive forces between molecules

6 Intermolecular Forces ion-ion ion-dipole ion-induced dipole dipole-dipole dipole-induced dipole induced dipole-induced dipole

7 Intermolecular Forces Van der Waals forces dipole-dipole dipole-induced dipole induced dipole-induced dipole

8 Ion-ion attractive force + cation anion. is an ionic bond very strong

9 ion-dipole attractive forces attractive forces between an ion and a polar molecule

10 ion-dipole attractive force

11 dipole -dipole attractive forces attractive forces between polar molecules

12 dipole-dipole attractive force

13 Hydrogen bonding A special type of dipole- dipole interaction A very strong dipole interaction

14 Hydrogen Bonding The dipole dipole interactions experienced when H is bonded to N, O, or F are unusually strong. We call these interactions hydrogen bonds. Intermolecular Forces 2012 Pearson Education, Inc.

15 dipole-dipole attractive force Hydrogen bonding δ δ+ δ+ δ δ+ δ δ δ+ δ δ+ δ δ+

16 dipole-dipole attractive force Hydrogen bonding

17 Importance of Hydrogen Bonding boiling point depends on intermolecular forces in liquid state compound MW µ Bp, C CH 3 CH 2 CH CH 3 CH 2 OH

18 B.P. ( C) H 2 0 Hydrogen bonding in H O 2 H Se 2 H 2 Te -100 H 2 S SnH CH 4 SiH 4 GeH 4 period

19 Hydrogen bonding important in compounds with OH bonds water, alcohols, acids, carbohydrates NH bonds ammonia, amines, peptides, proteins, nucleic acids FH bonds

20 Importance of Hydrogen Bonding hydrogen bonding in - proteins - nucleic acids (DNA and RNA)

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24 Dispersion forces attractive forces that result from temporary dipoles induced in an atom or molecule

25 ion-induced dipole attractive force Polarizability: the ease with which the electron distribution surrounding an atom is distorted by an external electric field

26 Polarizability increases with size of atom fluorine very nonpolarizable ( hard ) iodine very polarizable ( soft )

27 Dipole-induced dipole attractive forces + +

28 Induced dipole-induced dipole attractive forces (London Forces) + +

29 London Dispersion Forces London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole Pearson Education, Inc. Intermolecular Forces

30 Factors Affecting London Forces The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n-pentane) tend to have stronger dispersion forces than short, fat ones (like neopentane). This is due to the increased surface area in n-pentane Pearson Education, Inc. Intermolecular Forces

31 Factors Affecting London Forces The strength of dispersion forces tends to increase with increased molecular weight. Larger atoms have larger electron clouds that are easier to polarize. Intermolecular Forces 2012 Pearson Education, Inc.

32 Which Have a Greater Effect? Dipole Dipole Interactions or Dispersion Forces If one molecule is much larger than another, dispersion forces will likely determine its physical properties. If two molecules are of comparable size and shape, dipole dipole interactions will likely be the dominating force Pearson Education, Inc. Intermolecular Forces

33 Approximate magnitudes of intermolecular forces Force Energy, kj/mol ion-ion ion-dipole ion-induced dipole dipole-dipole dipole-induced dipole induced dipole induced dipole