Chapter 6 Intermolecular Forces and Shapes

109.5 degrees

Reduces bonding angle by 2.5 degrees

Solid Wedge= Towards us (too real too close) Dashed Wedge= Away from us (running away, fading)

Electrons are a cloud of negative charge. The theory is that electrons pairs will repels each other, occupying the position which will minimise repulsion the most.

1= Tetrahedral 2= Pyramidal 3= Non Linear

1=Trigonal Planar, 120 degrees 2=Octahedral, 90 degrees

• Find the number of bonding regions (double bonds count as one entity) on the central atom • Find the number of lone pairs of electrons • The total number of both of these will determine the starting angle e.g PH3, 4, start with 109.5 degrees, minus 2.5*n.of.lone pairs • Figure out shape dependent on number of bonding regions and lone pairs leg PH3, 3 bonds, 1 lone, pyramidal

Bonded Pair/ Bonded Pair Bonded Pair/ Lone Pair Lone Pair/ Lone Pair

The strong electrostatic force of attraction between a shared pair of electrons and the nuclei of the bonded atoms

The measure of the tendency of an atom to attract a shared pair of electrons in a covalent bond

It is formed when there is a different in electronegativity between the atoms in a covalent bond. The one with higher electronegativity forms a slight negative change, pulling the electrons more, and the other a slight positive charge. It is caused by the unequal distribution of electron density in a covalent bond.

Atomic radius increases as more shells are present There is more electron shielding Electronegativity decreases

Same number of shells, so same amount of shielding Nuclear charge increases as number of protons increases Atomic radius increases slightly due to increased charge, pulled inwards So electronegativity increases

The separation of opposite charges

0-0.4= Pure Covalent 0.4-1.8=Polar >1.8=Ionic

A difference in electronegativity The molecules is not symmetrical, so the dipoles do not directly oppose and do not cancel out (Dependent on shape)

Weak interactions between dipoles of different molecules

Due to the random movement of electrons, there is an unequal distribution of negative charge. At any instant, an instantaneous dipole is produced. An instantaneous dipole will induce a dipole on a neighbouring molecules These induced dipoles will induce dipoles on further neighbouring molecules, which are then attracted to one another

The larger the number of electrons, the larger the instantaneous dipoles, producing greater attraction More energy is needed to overcome the stronger London forces

F2 has only London forces to overcome. H-Cl has both London forces and permanent-dipole-dipole interactions as it is a polar molecule. The intermolecular forces is therefore stronger. This means more energy is needed to overcome the intermolecular forces and a higher melting point

In solid, simple molecular lattice Molecules held together by weak intermolecular forces- London forces, maybe permanent dipole These are broken at low temperatures, as little energy is needed to overcome them Atoms in the molecule are covalently bonded, not overcome

Will dissolve in non-polar solvents Interactions between non polar simple and non polar solvent, cause dissolving Will not dissolve in polar solvents Intermolecular forces within solvent too strong to overcome by interactions between the two

Depends on the strength of the dipoles, shape… Some have hydrophobic and hydrophilic components

No. No mobile charge carriers