CH3.3 Chemistry of the p-block Flashcards
how many oxidation states do elements in the p block normally have and why this amount
2 becuase one of them equals the group number and one is is two less then that.
iner pair effect
The tendancy of S2 pairs of electrons in an atom to stay paired leading to a lower oxidation state
octet expansion
The ability of some atoms to use d-oribtals to have more than eight electrons in their valence shell.
trend of stability of oxidation states in the p block
stability of lower oxidation states become greater down the group.
name for , tendency of heavier atoms to form lower oxidation states
inert pair effect
where does the inert pair effect hapen (which groups)
lower elements of group 3,4 and 5
why can elements in period 2 not have more then 8 bonds
period 2 elements do not have accsses to the d-orbitals, so they can not octet exspand meaning there are only eight electrons in the outer shell availbale for bonding.
amphoteric
materials react with both acids and bases
how do we show that something is amphoteric
we react it with a acid and a base
p block elements form amphoteric …..
oxides
when showing that something is amphoteric what are the chemicals we normally react it with
nitric acid or hydrochloric acid
and
sodium hydroxide
equation to show that aluminium oxide is amphoteric
Al2O3 + 6HCL –> 2AlCl3 + 3H2O
AL2O3 + 2NaOH + 3H2O –> 2Na(Al(OH)4)
What happens when sodium hydroxide is added to a solution contatining a amphoteric metal compound.
a precipitate of the metal hydroxide is formed. Since the hydroxide can react with more sodium hydroxide these precipitates will then redissolve.
equation for sodium hydroxide being added to a solution of a amphoteric metal compoud (e.g.Aluminiumoxide)
amphoteric metal compound - Al2O3
Al3+ + OH- –> Al(OH)3
Al(OH)3 + OH- –> (Al(OH)4)- excess sodiumhydroxide
electron deficeitn atom
a atom that does not have a full outer shell of electrons
how many bound do group 3 elements normally form in covalent bonds
3
what type of bonding is common in electron deficient species and why
co-ordinate bonding, because it wants to gain extra electrons pairs
how do electron deficient species form co-cordinate bonds
2 possible ways
they react with outher compounds or by forming dimers.
how do dimers work
each elelctron deficient compound uses a lone pair of electons from another electron deficient species to form coordinate bones.
give a exsample of a dimer
aluminium chloride in gas phase
what type of compound is a dimer classsed as and why
a donar-acceptor compound, because one molecule donates a lone pair and the other accepts it.
name to typese of boron nitrat
hexagonal boron nitride and cubic boron nitride
hexagonal boron nitride
- structure
- forces
- electrons
- bond
- layed hexagonal network of borons and nitrogen (ionic bonds in hexagonal shapes)
- structure similiar to graphite
- atoms in different layers lie directly above each other boron has a nitrogen directly above and below (not the same as graphite)
- weak van deer waal forces joining the layers together
- no delocalised electrons meaning it can’t conduct electricity
- B-N bonds are polar
uses of hexagonal boron nitride and what allow sit to be good at this (2)
lubricant, becuase there are only weak van deer waals forces holding the layers of hexagonal structures together
good conductor so is used in electronics as a substnace for semiconductors, microwave-transparent windows, and structural material for seals, electrodes and cataltst carriers in fuel cells and batteries.
cubic boron nitride, structure and characteristics..
- combines three dimensionaly replacing the carbon in diamonds.
- very hard and britle
- high melting point (strong covalent bonds need to be brocken to melt)
uses for cubic boron nitrate and why is it good for this
wear-resistance coating and industrial abrasive, due to the strong covalent bonds.
oxidation states of group 4 elements
+2 and +4
trend in stability of oxidation state in group 4
stability of +2 oxidation state incerasises down the group as the inert pair eeffect becomes more significant. But the most stable oxidatino state for all the elements in group 4 is +4 appart from lead where the most stable is +2
most stable oxide of carbon
carbon dioxide
name the only stable compound of carbon containing +2 oxidation state
carbon monoxide
Co acts as ….. agent because ….
Co acts as a reducing agent because it is easily oxidised from +2 to +4
carbon monoxide is used for..
give a equation
reducing agent for metals from their oxides e.g.
copper
CuO + CO –> Cu +CO2
in general metal oxides can be classed as ……. and non-metals oxides as ……
in general metal oxides can be classed as BASIC OXIDES and non-metals oxides as ACIDIC OXIDES
what are the stable chlorides of carbon and silcion
the tetra chlorides CCl4 and SiCl4
what colour is CCl4
colourless
what colour is SiCl4
colourless
what shape is CCl4 and SiCl4
tetrahedral
octet exspansion
Is the ability of an atom to form species with more than eight electrons in the valence shell. These may be stable compounds such as SF6 or intermediate stage in a reaction mechanism such as the coordinate bonding of water and SiCl4
does CCl4 form with water? why
no, because it forms a sepreate layre under the water, this is because the carbon atoms can not combine bery easily with the water molecules due to there not being a orbital available in the valance shell meaning that octet exspansion can not occur.
observations when:
a solution containing lead(II) compounds (Pb2+) is added to NaOH
with equation
An inital white precipitate of Pb(OH)2 is formed
Pb+2(aq) + 2OH-(aq) –> Pb(OH)2 (s)
observations when:
a solution containing lead(II) compounds (Pb2+) is added to excess NaOH
with equation
The white precipitate redissolves in excess OH- (aq) to form the tertahydroxoplumbate (II) ion:
Pb(OH)2 (s) + 2OH- (aq) –> (Pb(OH)4)2- (aq)
observations when:
a solution containing lead(II) compounds (Pb2+) is added to HCL(aq)
with equation
A dense white precipitate of lead chloride, PbCl2 is formed
Pb2+ (aq) + 2Cl- (aq) –> PbCl2 (s)
observations when:
a solution containing lead(II) compounds (Pb2+) is added to KI (aq)
with equation
A dense bright yellow precipirate of lead iodide, PbI2 is formed:
Pb2+ (aq) + 2I- (aq) –> PbI2(s)
key observations reaction in orer to determin Pb(II) ions
a solution conatining Pb(II) ions produces a bright yellow precipitate when mixed with a solution of KI
the precipitate is (PbI2)
Trend of reaction of group four chlorides with water
reaction becomes more vigorous down the group as the bonds in the compound become weaker.
most stable chloride of lead
lead(II) chloride
Lead (II) chloride, colour, reaction with water,
white ionic solid that does not react wiht water and it can be dissoblev in hot water
oxidising power of group 7 elements and standard electrode potential trend
Oxidation power increases down the group therefore the standard electrode potential of the halogens also decreases down the group.
sodium chloride and sulfuric acid reaction
produces HCl gass
HCl is difficult to oxidise and so the sulfuric acis dosen’t cause any redox reactino
observation HCl steamy fumes
NaCl(s) + H2SO4(conc.) –> NaHSO4(s) + HCl(g)
sodium Bromide and sulfuric acid reaction
produces HBr gas,
sulfuric aci oxidises some of the HBr to form brown fumes of Br2 and SO2 gas
The hydrobromic acid is slightly easier to oxidise and so the sulfuric acid causes a redox reaction
observation -steady fumes of HBr gas, orange fumes of Br2
2HBr(s) + H2SO4(conc.) –> SO2(g) + Br2(g) + 2H2O(l)
reaction of sodium iodide to sulfruic acid
intially produces HI gas.
sulfuric acid easily oxidises the HI to form complex mixture of product including I2 SO2 and H2O
2HI(s) + H2SO4(conc.) –> SO2(g) + I2(s) + 2H2O(l)
observation - steady fumes of HI, purple fumes of I2 or black solid/brown solution ; smell of rotten eggs (H2S), yellow solid.
stabilty of higher oxidation states in group seven
higher oxidation states become more stable as you go down the group
Dispropotionation reaction
IS one in which the same lement is both oxidiesd and reduced, forming products contatining the elemt in two different oxidation states.
reaction when chlorine is bubbled through water
Cl2(g) + H2O(l) HCl(aq) + HOCl (aq)
