SHAPES OF MOLECULES.
Shapes of molecules:
5 groups=trigonal bipyramidal-90/120
3 pairs and 1 lone=pyramidal-109
2 pairs and 2 lone=bent-109
3 groups=planar triangular-120
2 groups=linear 180
REMEMBER! Electrons repel eachother as far as possible=shape of molecules.
Enthalpy change of combustion (kJmol-1) =Energy transferred (kJ)/moles of fuel used.
Shorter bonds have higher bond enthalpies than longer ones.
Shorter bonds are stronger than longer ones.
Double bonds are shorter than single bonds.
Standard enthalpy change of combustion-the enthalpy change when 1 mole of a substance burns completely in oxygen under standard conditions=298K
Aliphatic=No ring structures: Alkanes, Alkenes, Cycloalkanes.
Aromatic=Contain one or more benzene rings
Saturated=No double bonds.
Unsaturated=Contains one or more double bonds.
Group 2 oxides/hydroxides=bases that allow them to react with carbon dioxide/acids to form group 2 carbonates.
Solubility of group 2 carbonates decreases down the group.
Reactivity of group 2 increases down the group.
Thermal stability of group 2 carbonates increases down the group.
Cracking-breaking up long chain molecules, into shorter, branched and unsaturated molecules.
Zeolites-small sieve like holes, only allow straight chain molecules through.
Wedges-bonds in front of the plane of paper
Dotted lines-bonds behind the plane of paper.
Same element same protons different numbers of neutrons.