Chapter 6

• The electrons pair surrounding the central atom determine the shape of the molecule or ion • the electron pairs repel each other is they are arranged as far as possible • the arrangement of electron pairs minimises repulsion and holds the bonded atoms in definite shape • different numbers of electron pairs result in different shapes

• electron pairs repel as far away as possible • lone pairs repel more strongly than bonded pairs • lone pairs repel bonded pairs slightly closer together, decreasing the bond angle

2.5

• The central carbon atom is bonded to 2 other atoms • There are 2 regions of electron densities • The two bonded regions repel each other as far as possible • this gives the carbon dioxide molecule a linear shape • with bond angles of 180 degrees

Increases across periods Decreases down group Ignoring noble gases

A difference in charge between the 2 atoms caused by a shift of electron density in the bond

In a covalent bond, the bonding electrons are pulled towards the more electronegative atom This makes the bond polar The difference in electronegativity between the bonding atoms causes a permanent dipole • the d+ and d- on polar molecules cause weak electrostatic forces of attraction between molecules called permanent dipoles

Forces between molecules Weaker than covalent ionic and metallic

Induced dipole-dipole (London forces) Permanent dipole-dipole Hydrogen bonding (strongest)

They cause all atoms and molecules to be attracted to each other

• electrons in charge clouds are constantly moving • at any given point there will always be more electrons on one side of the cloud than the other, creating a temporary dipole • this causes another temporary dipole in the other direction of a neighbouring atom • because the electrons are constantly moving the dipoles are created and destroyed all the time

Size - larger molecules have larger electron clouds - stronger forces Surface area - they have a bigger exposed electron cloud This causes a higher boiling point

Low melting points - weak intermolecular forces , easily overcome by heat Polar molecules - compounds with hydrogen molecules can form hydrogen bonds with water and dissolve Not conductors - don’t have an overall charge

When a simple molecular compound is added to a non polar solvent intermolecular forces form between them Interactions weaken the intermolecular forces breaking them so that it dissolves

Too strong to be overcome No Interactions

Attract each other Depend on London forces

Lone pair Oxygen Fluorine Nitrogen