molecules

shape of SF6 molecule (6 bonding pairs)

-octahedral

-90 degree bond angles

shape of H2O molecule

-non linear

-109.5 - (2x2.5)= 104.5

pi bond

-formed by sideways overlap of 2 p-orbitals

-weaker than sigma bonds because electron density is spread out above and below nuclei

dative covalent bond

-a covalent bond where both electrons being shared originate from the same atom

covalent bond

-the electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms

average bond enthalpy

-a measurement of the strength of a covalent bond

BeCL2 molecule? (2 electrons bonding pairs)

-linear

-180 degree bond angle

BF3 molecule

-trigonal planar

-120 degree bond angle

CH4 molecule (4 electron bonding pairs)

-tetrahedral

-109.5 degree bond angles

PCl5 molecule(5 electron bonding pairs)

trigonal bipyramidal

120 and 90 degree bond angle

sigma bond

-formed when 2 s-orbitals overlap

-overlap in a straight line, giving highest electron density between 2 nuclei

-thus there are strong electrostatic forces between nuclei and electron pair

-e.g. C-H

What are some anomalous properties of water resulting from hydrogen bonding?

-ice is less dense than water bacause in ice, water molecules are held in a LATTICE by hydrogen bonds, which break when ice melts

-so ice has more hydrogen bonds than water and hydrogen bonds are relatively long, holding molecules further apart

-water has relatively high melting and boiling points because hydrogen bonds have to be broken

What are the requirements of induced dipole-dipole forces (London dispersion forces)

-only needs electrons, more electrons=stronger forces

-they're the weakest intermolecular force

What are the requirements for permanent dipole-dipole forces and how do they form?

-electronegativity difference between atoms (polar bond)

-asymmetric molecule (polar molecules have permanent dipoles)

-strength is intermediate, stronger when electronegativity difference is bigger

-negative end of molecule will attract postiive end of another

-e.g. HCl

What are the requirements for hydrogen bonds and how are they formed?

-hydrogen 

-attached to a lone pair

-an electronegaative atom (fluorine, oxygen, nitrogen)

-fromed by attraction between delta + and delta -

-they're the strongest, if number of lone pair matches number of H atoms, maximum number of hydrogen bonds form per molecule

What's the definition of electronegativity and what are polar bonds?

-the ability of an atom to attract a shared pair of electrons within a covalent bond

-fluorine, oxygen, chlorine and nitrogen are the most electronegative elements (top right of the periodic table)

-this makes polar bonds

lone pairs

-2 electrons in same orbital that aren't involved in forming covalent bonds

-for every lone pair around central atom, minus 2.5 from original bond angles without lone pairs

electron pair repulsion theory

-used to explain the shape and bond angles of molecules

-electrons pairs repel each other to get as far apart as possible

-lone pairs repel more than bonding pairs, pushing bonding pairs closer together

WHt's the shape of a molecule woth 6e- pairs? (4 bonding, 2 lone)

-square planar

-90 degree bond angle

What's the shape of a molecules with 3e- pairs, 1 lone and 2 bonding?

-non-linear

-120 - 2.5 = 117.5 degree bond angle

WHat's the shape of an NH3 molecule? (4 e- pairs, 3 bonding, one lone)

-trigonal pyramidal

-109.5-2.5 = 107 degree bond angle

requirements for polar molecule

-polar bond

-asymmetric molecules (so dipoles don't cancel out when they act in opposing directions

how are induced-dipole forces formed

-due to electrons moving quickly/randomly, giving molecule a temporary dipole

-instantaneous dipole on one atom/molecule induces a dipole on neighbouring atom/molecule