3.3 chemistry of the p-block Flashcards
why are p-block elements called p-block elements?
as they have their outermost electron in the p-orbital
which groups are p-block elements found in?
groups 3 to 0
elements at the top of each group in the p-block are non-metal, whilst those at the bottom of groups 3-6 are metals.
what does this region of change within each group lead to?
some changes in bonding and consequential physical and chemical properties
what are the two oxidation states that p-block elements in groups 3,4,5 and 6 usually show?
- the higher oxidation state corresponds to the group number
- the lower oxidation state is usually two lower
e.g group 3 element would have oxidation states of +3 and +1
of the two oxidation states that p-block elements that groups 3,4,5 and 6 usually have, one of the oxidation states will be more stable than the other.
what will this depend on?
- octet expansion
- the inert pair effect
what is octet expansion?
the ability of elements to use available d-orbitals so that there are more than 8 electrons in the outer shell
(the molecules formed are sometimes called hypervalent)
in group 3, what are the (sometimes two) oxidation states of B, Al, Ga, In, Tl?
which one is most stable?
B = 3
Al = 3
Ga = 1, 3 (3 most stable)
In = 1,3 (1 most stable)
Tl = 1,3 (1 most stable)
in group 4, what are the (sometimes two) oxidation states of C, Si, Ge, Sn, Pb?
which one is most stable?
C = 2,4 (4 most stable)
Si = 4
Ge = 2,4 (4 most stable)
Sn = 2,4 (4 most stable)
Pb = 2,4 (2 most stable)
in group 5, what are the (sometimes two) oxidation states of N, P, As, Sb, Bi?
which one is most stable?
N = 3,5 (both most stable)
P = 3,5 (both most stable)
As = 3,5 (3 most stable)
Sb = 3,5 (3 most stable)
Bi = 3,5 (3 most stable)
the stability of the lower oxidation states (increases/decreases) down the group
increases
what is the inert pair effect?
- the tendency of the outermost electrons to remain unshared
- leading to a lower oxidation state
for an element in group 4, the outer electronic configuration is ns^2 np^2
- when the element has an oxidation state of 4, it involves all four electrons
- when the element has an oxidation state of 2, the inner two electrons do not become involved, and this ns^2 pair is called the inert pair
- some elements in groups 5,6 and 7 are able to form compounds with more than 8 electrons in the outer shell
e.g phosphorus can form PCl5 with 10 electrons in the outer shell of the phosphorus atom
- but, some group 3 elements are also an exception to the octet rule.
- aluminium and boron can form compounds with fewer than 8 electrons in the outer shell
- e.g the boron atom in BF3 will have a share of only 6 bonding electrons and we say that the boron atom is electron deficient
in groups 3,4 and 5, the lower oxidation states of the element are more stable the lower down the group you go, due to the inert pair effect
- in group 4, tin has a more stable oxidation state of +4
- so SnCl4 is more stable than SnCl2
- but lead, which is lower down the group, has a more stable oxidation state of +2
- this is because the s2 electrons in lead are not able to take part in bonding - as a result, they are called the inert pair
explain why boron forms compounds with the +3 oxidation state alone, but thallium compounds are more stable with the +1 oxidation state [2]
- +1 occurs due to inert pair of s-electrons
- inert pair effect becomes more significant down the group
what are amphoteric substances?
- ones that can act as both acids and bases
what are the examples of amphoteric substances?
- Al 3+ / Al (Al2O3)
- Pb 2+ / Pb (PbO)
what is the equation of aluminium acting as a base?
Al2O3 + 6HCl —> 2AlCl3 + 3H2O
what is the equation of aluminium acting as an acid?
Al2O3 + 2NaOH + 3H2O —> 2Na[Al(OH)4]
what is the equation of lead acting as a base?
PbO + 2HNO3 —> Pb(NO3)2 + H2O
(or PbO + 2HCl —> PbCl2 + H2O)
what is the equation of lead acting as an acid?
PbO + 2NaOH + H2O —> Na2[Pb(OH)4]
group 3 elements, like aluminium and boron, are so-called because they have 3 electrons in their outer shell. this means they are only able to form 3 covalent bonds, giving 6 electrons in the outer shell of the group 3 atoms
what does this cause?
electron deficiency
- because of electron deficiency, aluminium and boron are able to form ______ _______ with a lone pair of electrons from another atom to gain a stable octet
- coordinate bonds
therefore, they are called electron acceptors and can form dimers