p block elements Flashcards
What are the features of the p block elements?
Most p block elements can adopt more than one oxidation state.
- Boron, (carbon), silicon, nitrogen and phosphorus are semi/non-metals.
- Form discrete molecules and polymers (rings and chains) that are generally poor conductors of electricity.
- Down a group, there is more metallic character and larger radii that allow for higher coordination numbers.
- First element of each group shows different chemistry due to (the number of electrons?).
What is catenation?
The linkage of atoms of the same element into longer chains. Catenation occurs most readily in carbon, which forms covalent bonds with other carbon atoms to form longer chains and structures.
What are the trends down the p block groups?
Down the group, multiple single bonds between atoms of the same element are preferred to double bonds.
- Down the group, there is an increasing s-p gap, so there is less favourable hybridisation.
What are the features of group 13 (3) elements?
ns2.np1, where n is the shell number. There are 3 valence electrons, so the maximum oxidation state is +3. Aluminium is the most abundant group 13 element. There is an increase in metallic character from boron to thallium
Lewis base
A species with a pair of electrons available for donation (donor), e.g. H2O, NH3, F- and other halogens.
Lewis Acid
Species capable of accepting a pair of electrons (acceptor), e.g. BX3, AlCl3, transition metals.
The relative order of ease of electron acceptance by BX3
BF3 < BCl3 < BBr3 < BI3. Iodine accepts the most electron density.
Why is BF3 a weak Lewis acid?
One might think that as F is the most electronegative element that BF3 would be the most electron deficient molecule, but the F atom is of similar size to B, so forms a stronger p bond (as there’s better overlap)m giving the most stable BX3 structure. Therefore, BF3 needs additional electron density the least, as is a weak Lewis acid. BI3 is the strongest lewis acid in the series.
