Electronegativity, Polar Bonds, and Polar Molecules Thursday February 23 rd, 2006 .

Electronegativity, Polar Bonds, and Polar Molecules

Thursday February 23rd, 2006

http://charlescurtis.ca

Polar Covalent Bond

When the two atoms in a covalent bond are different, one atom will have a greater attraction towards the electrons.

On average the electrons will spend more time around the atom with a greater electronegativity.

This creates a polar bond. Slight build up of charge on an each atom in

the covalent bond.

Electronegativity

Measure of the attraction of the electrons towards an atom in a covalent bond.

A higher value means a greater attraction.

Polar Bond

One atom in the bond will become slightly positively charged while the other atom will become slightly negatively charged.

The atom with the higher electronegativity will be slightly negatively charged (δ-)

The atom with the lower electronegativity will be slightly positively charge (δ+)

Methanol

Using Electronegativity to Predict the type of bonding (Ionic vs Covalent)

Polar Molecules

Covalently bonded molecules, (which contain bonds from two different atoms), which are not symmetrical will form POLAR MOLECULES

The symmetry of symmetric molecules cancels out the effect of polar bonds.

Polar Molecules will have a positive end and a negative end. CH4

CCl4 CO2

Intermolecular Forces

van der Waals Forces dipole-dipole forces London Dispersion Forces

Hydrogen Bonding

Dipole-dipole

Much weaker than ionic or covalent bonds

London Dispersion Forces

There are always weak forces holding molecules together.

Causes by temporary dipole-dipole interactions caused by fluctuations of electron cloud.

Weaker than dipole-dipole forces

Hydrogen Bonding

Water Molecule vs Chlorine Gas Compare Molecular Masses.

Water = 18 g/mole Chlorine gas =70 g/mol

All things being equal (but mass), which would boil easier?

Hydrogen Bonding

High or Low Intermolecular Forces

Atmospheric Gases H2

CH4

N2

O2

Sugar NH3

In Class Homework Assignment

p84 #1-4 p88 #8-12

Due at the end of class

When done homework, start reading section 2.5, which is on naming compounds.

Section 2.5 is the last section of Chapter 2.

Quiz Friday on section 2.1 to 2.3

Test sometime mid next week.

Article Assignment Due Next Tuesday. A lot of Article Assignment #1 not handed in.