Intermolecular Bonds

Special Properties of Water

- much weaker and determine physical state of substance

Three types of intermolecular bonds:

Intermolecular BondsIntramolecular bonds - hold atoms in a molecule together

London forces

Dipole-dipole forces

Hydrogen bonds

Intermolecular bonds - hold two or more molecules together

Collectively known as van der Waals forces

London Forces - cause bonds that are formed due to a temporary unequal distribution of electrons in an atom

London Forces

Very weak, occur between small nonpolar molecules (ex: methane)

CH4

That is why methane is a gas at room temperature

Each molecule is weakly

attracted to its neighbour

Cumulative effect of London forces become more significant in large nonpolar molecules (ex: octane)

London ForcesLondon Forces - cause bonds that are formed due to a temporary unequal distribution of electrons in an atom

Very weak, occur between small nonpolar molecules (ex: methane)

In larger molecules, many weak attractive

forces result in a closer association

C8H18

As a result, octane is a

liquid at room temperature

Slightly positive end of one polar molecule is attracted to slightly negative end of another polar molecule

Stronger than London forces

Dipole-dipole Forces

δ+

δ-

δ+δ-

δ+

δ-

δ+δ- δ-

δ+

HCl

Dipole-dipole Forces - occur between polar molecules, like HClT

Hydrogen Bonds

δ+δ+

δ-

δ-δ+δ+

δ-δ+δ+

δ- δ+

δ+

δ+δ-δ+δ+

δ+δ-

δ+δ+

δ-δ+

δ-δ+

δ+

δ-δ+

Hydrogen Bonds - dipole-dipole forces that form between electropositive H of one polar molecule and an electronegative N, O, or F of anotherStrongest intermolecular force

IntRAmolecular IntERmolecularHolds one molecule

togetherHolds many molecules

togetherStrong attraction between

atomsWeak attraction between

molecules

Commonly called “bonds” Known as van der waals forces

Determines if electrons are transferred or shared

Determines state of substance

Ex: Ionic, covalent, polar covalent

Ex: London forces, dipole-dipole, hydrogen bonds

Special Properties of Water

Unique Properties of Water

Water is an excellent solventi.

Hydrogen bonding and the angular shape of a water molecule gives it unique properties essential to existence of living things

Solvent - substance that is able to dissolve other substances

Water is a polar molecule

Break ionic bonds

Unique Properties of Water

Water is an excellent solventi.Water is both adhesive and cohesiveii.

Adhesive - tendency of dissimilar particles/surfaces to cling to one another

Cohesive - tendency of similar or identical particles/surfaces to cling to one another

Hydrogen bonding and the angular shape of a water molecule gives it unique properties essential to existence of living things

Unique Properties of Water

Water is an excellent solventi.Water is both adhesive and cohesiveii.Water has a high specific heat capacityiii.

Hydrogen bonding and the angular shape of a water molecule gives it unique properties essential to existence of living things

Specific Heat Capacity - amount of energy needed to change the temperature of 1 kg of a substance by 1°C

Water resists change in temperature

Unique Properties of Water

Water is an excellent solventi.Water is both adhesive and cohesiveii.Water has a high specific heat capacityiii.Water has a high heat conductivityiv.

Hydrogen bonding and the angular shape of a water molecule gives it unique properties essential to existence of living things

Water has a high boiling/freezing pointv.Water is more dense as a liquid then as a solidvi.