Scribd
Upload
621 views18 pages

Intermolecular Forces

The document discusses different types of intermolecular forces (IMF) that exist between molecules, including dispersion forces, dipole-dipole forces, hydrogen bonding, and ion-dipole forces. Dispersion forces are the weakest and result from instantaneous dipoles that induce dipoles in nearby molecules. Dipole-dipole forces occur between polar molecules with partial charges. Hydrogen bonding is an even stronger attraction between a hydrogen atom covalently bonded to an electronegative atom like N, O, or F, and another electronegative atom. Ion-dipole forces involve attractions between ions and polar molecules. The strength of IMF increases from dispersion to dipole-dipole to hydrogen

Uploaded by

api-263909505
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
621 views18 pages

Intermolecular Forces

The document discusses different types of intermolecular forces (IMF) that exist between molecules, including dispersion forces, dipole-dipole forces, hydrogen bonding, and ion-dipole forces. Dispersion forces are the weakest and result from instantaneous dipoles that induce dipoles in nearby molecules. Dipole-dipole forces occur between polar molecules with partial charges. Hydrogen bonding is an even stronger attraction between a hydrogen atom covalently bonded to an electronegative atom like N, O, or F, and another electronegative atom. Ion-dipole forces involve attractions between ions and polar molecules. The strength of IMF increases from dispersion to dipole-dipole to hydrogen

Uploaded by

api-263909505
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 18

INTERMOLECULAR

FORCES

Strength of intermolecular attraction

INTRAparticle VS
Forces within compound
bonds

INTERparticle
Attractive force between particles.
*keeps matter in solid or liquid
phase*

Types of Intermolecular Forces (IMF)


Dispersion (aka London Dispersion)
Dipole-Dipole

Hydrogen Bonding
Ion- Dipole

Dispersion

(London Dispersion)

Forces

Motion of e- in atom or molecule can


create an instantaneous dipole

Dispersion

(London Dispersion)

Forces

Instantaneous dipoles causes attraction


between atoms
Strength of attraction depends on Polarizability
Polarizability is ease of charge distribution

(how easy

is it to squash e-cloud)

# of e- in atom/molecule = Polarizability
Mass = Polarizability

Polarizability = Strength Dispersion Force

What accounts for the difference in boiling


points between the two molecules?
SiH4

bp 161K

CH4

bp 91K

Dipole-Dipole Forces
Permanent dipole in polar molecules

Attraction between positive and negative ends in polar molecules


Align themselves to maximize attraction & minimize repulsion

Larger dipole = Stronger Attraction

Dipole-Dipole Forces
Acetonitrile, CH3CN

Dipole-Dipole Forces
Acetonitrile, CH3CN

41 amu
bp 355K

Propane C3H8

44 amu
bp 231K

Propane

Dimethyl ether

CH3CH2CH3
MW 44amu
= 0.1 D
bp 231K

CH3OCH3
MW 46amu
= 1.3 D
bp 248K

Acetaldehyde

CH3CHO
MW 44amu
= 2.7 D
bp 294K

Acetonitrile

CH3CN
MW 41amu
= 3.9 D
bp 355K

Moving from left to right, do the dispersion forces


get stronger, get weaker, or stay roughly the same
in these molecules?

Hydrogen Bonding
Attraction between a H atom attached to highly electronegative
atom and nearby electronegative atoms

Occurs when H bonded to N, O, or F atoms


H atoms interacts w/ nonbonding e- pairs
H F

H F
H
H O

H N

Hydrogen Bonding
Makes water incredibly amazing & unique!!!

Ion-Dipole
Focuses on making solutions (dissolving in solvents)
Solubility: measure of how easily dissolved something is in another
substance

Attraction between ions & polar molecules

Cl-

Comparing IMF
no

no

Are ions present?

Are polar molecules


present?

yes

Are polar molecules


present?

Are H atoms
bonded to N, O, or
F atoms?
no

Dispersion
Forces Only

DipoleDipole
Forces

yes

no

yes
yes

Hydrogen
Bonding

Increasing Interaction Strength

Ion-Dipole
Forces

Ionic
Bonding

Comparing IMF
It is important to note that while the chart is a great indicator
of the strengths of forces of attraction, ALL substances have
dispersion forces and sometimes the stronger forces (dipoledipole) make a smaller contribution so may not be greater for
the molecule overall.
Name
Dichloromethane

Lewis Dot Diagram


Cl

Boiling Point (C)

Vapor Pressure at 20
C (mmHg)

39.6

353

76.7

89

H C Cl
H

Carbon Tetrachloride

Cl
Cl C Cl
Cl

You might also like