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Chapter 10 Liquids, Solids, and Phase Change. Why Do Solids and Liquids Exist?. Intermolecular Forces gases – Little to no attraction between molecules. Why Do Solids and Liquids Exist?. Intermolecular Forces liquids – Fairly strong forces between a

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why do solids and liquids exist
Why Do Solids and Liquids Exist?
  • Intermolecular Forces

gases – Little to no attraction between

molecules

CHM 112 M. Prushan

why do solids and liquids exist3
Why Do Solids and Liquids Exist?
  • Intermolecular Forces

liquids – Fairly strong forces between a

few molecules

CHM 112 M. Prushan

why do solids and liquids exist4
Why Do Solids and Liquids Exist?
  • Intermolecular Forces

solids – Strong forces prevent large amount of motion between molecules/atoms

CHM 112 M. Prushan

what makes a molecule polar
What makes a molecule polar?
  • Polar molecules are said to possess a permanent dipole moment.
  • Dipole moment measured in units of

Debye (Q x r ) [charge x distance]

1 D = 3.336 x 10-30 coulomb meters

Prof. Peter Debye

Noble Prize 1936

CHM 112 M. Prushan

dr prushan enough physics what does it mean
Dr. Prushan, enough physics, what does it mean?
  • OK… Let’s go back to Lewis Structures and VSEPR
  • Examples:

Draw Lewis Structures and Predict the Geometry of : NH3, H2O, CH4, CH3Cl,CHCl3 CO2, CCl4

(Yes, there was a reason you needed this)

CHM 112 M. Prushan

examples

CH4

CH3Cl

CHCl3

CCl4

NH3

H2O

CO2

Trigonal Pyramidal

Bent

Linear

Examples

Tetrahedral

CHM 112 M. Prushan

slide8

NH3

H2O

CO2

Trigonal Pyramidal

Bent

Linear

Polar or Not Polar That is the Question?

CHM 112 M. Prushan

slide9

NH3

H2O

CO2

Trigonal Pyramidal

Bent

Linear

Polar or Not Polar That is the Question?

m = 1.47 D

m = 1.85 D

m = 0 D

d -

d -

d +

d +

d -

d +

d -

CHM 112 M. Prushan

slide10

CH4

CH3Cl

CHCl3

CCl4

d -

d +

d -

d +

Polar or Not Polar That is the Question?

m = 0 D

m = 1.87 D

m = 1.90 D

m = 0 D

CHM 112 M. Prushan

types of intermolecular forces
Types of Intermolecular Forces
  • 4 main types of intermolecular forces

(1) London (Dispersion) Forces

(2) Dipole-Dipole Forces

(3) Ion-Dipole Forces

(4) Hydrogen Bonds

Increasing

Strength

CHM 112 M. Prushan

london dispersion forces
London (Dispersion) Forces

Weakest of the IM forces. All molecules have Dispersion forces

Result of interactions between instantaneous dipole moments.

Prof. Fritz London

CHM 112 M. Prushan

dipole dipole forces
Dipole-Dipole Forces
  • Result of permanent dipole moments in polar molecules

CHM 112 M. Prushan

ion dipole forces
Ion-Dipole Forces

The force which dissolves ionic compounds

A result of interactions between ions and solvent molecules

CHM 112 M. Prushan

hydrogen bonds
Hydrogen Bonds
  • Strongest of the intermolecular forces
  • NOT a chemical bond
  • MUST contain hydrogen covalently bonded to F, Cl, O or N.
  • Essential for Life!

CHM 112 M. Prushan

hydrogen bonds16
Hydrogen Bonds

If the boiling point of CO2 is , and CS2 is

Molecules with larger molecular weights have higher boiling points.

So why is H2O a liquid, but H2S is a gas?

CHM 112 M. Prushan

bonds
BONDS…

Hydrogen Bonds

CHM 112 M. Prushan

hydrogen bonds and life
Hydrogen Bonds and Life
  • Life Depends of H-bonds
  • The “Stuff” of Life relies on them to stay together

Proteins, Enzymes

Nucleic Acids (DNA, RNA)

Sugar-phosphate Backbond and

Base Pairs

Amino Acids

CHM 112 M. Prushan

slide20

Amino acids bond together to make polypeptides

The polypeptides fold to make the secondary structure of proteins

How and Why does the alpha structure form??

Linus Pauling Discovered How, in 1948

While in bed with a cold…. Lets let him describe how…

CHM 112 M. Prushan

slide21

Now let’s try that…

Come on down and get a polypeptide

CHM 112 M. Prushan

slide24

Which goes with which ???

A – T

G – C

Right??? BUT WHY????

Come on down and get some base pairs

CHM 112 M. Prushan

effect of intermolecular forces on melting and boiling points of molecular covalent substances
Effect of Intermolecular forces on melting and boiling points of molecular covalent substances

Why does HF have the highest BP?

Molecular wts.

132

20

77

81

32

16

128

37

Molecular wts.

BONDS…

Hydrogen Bonds

Increase only due to increase in MW,

Since all are non-polar

CHM 112 Summer 2007 M. Prushan