3.3 chemistry of the p block Flashcards
p-block groups 3,4 ,5 and 6 show how many oxidation states
2 oxidation states,
the higher oxidation state corresponds to the group number and the lower oxidation state is usually 2 and lower.
what is octet expansion
is the ability of elementws to use the available d orbitals so that there are more than 8 electrons in the outer shell.
the molecule formed are sometimes called HYPERVALENT,
What groups can expand their octet?
Some elements in Groups 5, 6 and 7 are able to form compounds with more than 8 electrons in the outer shell. For example, phosphorus can form PCl5 with 10 electrons in the outer shell of the phosphorus atom.
what group 3 elements are an exception to the octet rule
Aluminium and Boron can form compounds with fewer than 8 electrons in the outer shell. For example, the boron atom in BF3 will have a share of only 6 bonding electrons and we say that the boron atom is electron deficient.
Nitrogen is also in group 5 but cannot form 5 covalent bonds. why can’t it expand its octet?
2s electron cannot be moved because theres no space to move electrons to 2s2 to 3s
Explain why boron forms compounds with the +3 oxidation state alone, but thallium
compounds are more stable with the +1 oxidation state
+1 occurs due to inert pair of s-electrons (1)
Inert pair effect becomes more significant down the group (1)
define electron deficient
is one that does not have a full outer shell.
ie has fewer than 8 electrons in outershell.
what is the inert pair effect
is the increasing reluctance as you move down the group of the s2 pairs of electrons in the bonding level to become involved in bonding.
what is the trend of the inert pair effect as you go down the groups
As you go down the groups 3,4,5 the lower oxidation states become more stable the lower down you go.
what is the exception to the inert pair effect rule
tin is more stable in its +4 oxidation state than lead, despite lead being more lower down.
this is because the s2 electrons in lead are not able to take part in bonding and as a result are called an inert pair.
define amphoteric
Amphoteric substances can react with both acids and bases.
Write the equation of aluminium as a base
Al2O3 + 6HCl —> 2AlCl3 + 3H2O
write the equation of aluminium as an acid
Al2O3 + 2NaOH +3H2O —> 2Na[Al(OH)4]
write the equation of lead as a base
PbO + 2HNO3 –> Pb(NO3)2 +H2O
Write the equation of lead as an acid
PbO + 2NaOH +H2O –> Na2[Pb(OH)4]
Define dimer
formed when two of the same molecule join together
how do aluminium and boron form a stable octet
form co ordinate bonds with a lone pair of electrons from another atom to gain a stable octet.
how do you form Al2Cl6
two monomers of alcl3 are able to form dimer of al2cl6
define a donor acceptor compound
Donor acceptor compounds form where a lone pair is donated by one compound and accepted by another, forming a co-ordinate bond
define isoelectric
same number of electrons
what is hexagonal boron nitride
Hexagonal boron nitride (h-BN) can form a structure that is similar to graphite.
DIFFERANCES TO GRAPHITE.
Atoms in adjacent layers of h-BN are in register (aligned). In graphite they are out of register.
Π-electrons are relatively evenly delocalised in graphite but more localised in h-BN, as each nitrogen atom in h-BN has a lone pair of electrons. This makes BN an insulator.
There is an electronegativity difference between B and N which gives polar B-N bonds, whereas there is no electronegativity difference between the carbon atoms in graphite as all of the atoms are the same.
What is H-BN used for
h-BN is used in electronics for semi-conductors, ceramics and in microwave windows. It can also be used as a catalyst carrier in fuel cells and batteries
what is cubic boron nitride
Cubic boron nitride (c-BN) has the same properties and structure as diamond.
It is therefore hard, strong and has an extremely high melting point.
It is used as an industrial abrasive and is preferred to diamond for grinding certain materials. Although diamond is harder, due to the lack of electronegativity difference between atoms, c-BN is more stable. Diamond can react with transition metals like iron and above 800oC can react with air to form carbon dioxide.
