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
group 3 elements e.g aluminium and boron are called _____ _____ and can form _____?
- electron acceptors
- dimers
the aluminium in aluminium chloride is electron deficient
because the aluminium in aluminium chloride is electron deficient, how many monomers of aluminium chloride AlCl3 are able to form a dimer of Al2Cl6?
2
when do donor acceptor compounds form?
where a lone pair is donated by one compound and accepted by another, forming a co-ordinate bond
e.g boron trifluoride accepting a lone pair from the nitrogen in ammonia to form NH3BF3
state what is meant by the term electron deficient? [1]
- OUTER shell of electrons is not full / has fewer than 8 electrons
when BCl3 is mixed with ammonia a new species is formed. identify the new species and explain how it forms [2]
- NH3.BCl3
- coordinate bond forms between lone pair on N and electron deficient BCl3
the bond between boron and nitrogen has an analogy with the _____-______ bond
carbon-carbon
both boron-nitrogen and carbon-carbon have a total of 12 electrons on the two atoms which is called ______
isoelectronic
boron nitride and carbon-carbon bonds have almost the same atomic radii and a similar relationship in their electronegativities.
what does this mean for boron nitride?
it can exist in forms similar to that of the allotropes of carbon such as graphite and diamond
what are the two forms of boron nitride?
- cubic boron nitride (c-BN)
- hexagonal boron nitride (h-BN)
hexagonal boron nitride can form a structure that is similar to _____?
graphite
what are some differences between hexagonal boron nitride and graphite?
- atoms in adjacent layers of h-BN are in register (aligned). in graphite, they are out of register
- BN is an insulator
- there is an electronegativity difference between B and N which gives polar B-an bonds, whereas there is no electronegativity difference between the carbon atoms in graphite as all of the atoms are the same
- h-BN cant conduct electricity as has no delocalised electrons
what is h-BN used in?
- electronics for semi-conductors, ceramics and in microwave windows
- as a catalyst carrier in fuel cells and batteries
- single layers of h-BN can be wrapped to create nanotubes
cubic boron nitride (c-BN) had the same properties and structure as _____?
diamond
bc c-BN has the same properties and structure as diamond, it is :
- hard
- strong
- has an extremely high melting point
what is c-BN used as? (properties)
- an industrial abrasive
- is preferred to diamond for grinding certain materials
- although diamond is harder, due to lack of electronegativity difference between atoms, c-BN is more stable
(diamond can react with transition metals like iron and above 800°C can react with air to form carbon dioxide)
hexagonal boron nitride and graphite have similar structures. describe the differences between these two isoelectronic materials in terms of their bonding and structure [4 QER]
any 3
- all atoms the same in graphite / BN alternate in boron nitride
- atoms in layer of BN lie above each other but are not in graphite
- B-an bonds are polarised but graphite is non-polar
- p-electrons in BN are localised but in graphite are delocalised
group 4 elements show oxidation states +2 and +4.
what does the stability of these oxidation states depend on?
the inert pair effect
group 4 contains both metals, e.g tin and lead, non-metals e.g carbon and semi-metals e.g silicon.
the change in chemical and physical properties from the top to the bottom of the group are the most significant of any group
carbon dioxide, where carbon has an oxidation state of +4
carbon monoxide, where carbon has an oxidation state of +2
which is more stable?
carbon dioxide with an oxidation state of +4 is more stable
carbon monoxide will act as (an oxidising / a reducing) agent?
reducing agent
- as the carbon is easily oxidised from +2 to +4
what is an example of how carbon monoxide acts as a reducing agent?
- the extraction of iron in the blast furnace
- Fe2O3 (s) + 3CO (g) —> 2Fe (s) + 3CO2 (g)
lead (II) oxide PbO, has an oxidation state of +2
lead (IV) oxide PbO2, has an oxidation state of +4
which is more stable?
lead (II) oxide PbO with an oxidation state of +2 is more stable
PbO2 will act as (an oxidising / a reducing) agent?
an oxidising agent
- because lead is easily reduced from +4 to +2
what is an example of lead (IV) oxide acting as an oxidising agent?
- in its reaction with concentrated hydrochloric acid
PbO2 (s) + 4HCl(conc.) —> PbCl2 (s) + Cl2 (g) + 2H2O (l)
carbon dioxide is (acidic/basic/amphoteric)
why + examples
acidic
- as it dissolves in water to form the weak acid carbonic acid
CO2 (g) + H2O (l) ⇌ H+ (aq) + HCO3 - (aq) - will also react with alkalis, e.g NaOH, to form a salt
CO2 (g) + NaOH (aq) —> NaHCO3 (aq)
lead (II) oxide, is (acidic/basic/amphoteric)?
examples
- amphoteric
- so will react with both acids and bases
as a base:
PbO (s) + 2HNO3 (aq) -> Pb(NO3)2 (aq) + H2O
as an acid:
PbO (s) + 2NaOH (aq) + H2O —> Na2[Pb(OH)4] (aq)
what are the stable chlorides of carbon and silicon?
- the tetrachlorides (form using covalent bonding)
- CCl4
- SiCl4
(both colourless liquids)
what type of bonding does lead (II) chloride have? therefore, does it react with water?
ionic bonding
- therefore doesn’t react with water
(only dissolves in hot water)
what colour and state is lead (II) chloride?
white solid
does CCl4 react with water? why?
no
- forms a separate layer under the water
- bc carbon doesnt have the available d-orbital in valence shell
- so carbon cant expand its octet to form a coordinate bond with the lone pair of electrons from water molecule
- (also
- bc the chlorine atoms are very bulky and the carbon atom is very small so its hard for the oxygen to get near the carbon atom
- there is a lot of repulsion between the various lone pairs as the oxygen atom gets close to the chlorine atoms, which makes this transition state very unstable)
does SiCl4 react with water? why?
- yes
- reacts very quickly with water in hydrolysis reaction
- silicon had empty 3d orbitals which can accept a lone pair of electrons from the oxygen atom
(also maybe bc the silicon atom is relatively big so there is space for the oxygen atom on water to attack the silicon atom)
what does the reaction between SiCl4 react with water to form?
- a white precipitate of silicon dioxide
- steamy, white fumes of hydrogen chloride HCl gas
SiCl4 (l) + 2H2O (l) —> SiO2 (s) + 4HCl (g)
how is SiCl4 able to react with water in the way it does?
- as silicon has vacant 3d orbitals with which the water can form co-ordinate bonds
what are the 4 reactions of solutions of lead compounds Pb2+ (aq) you need to know?
- with NaOH (aq) (OH-)
- with excess NaOH (aq) (OH-)
- with HCl (Cl-)
- with KI (I-)
what is the observation of the reaction of lead with NaOH?
- a white ppt of lead hydroxide will be formed
Pb2+ (aq) + 2OH- (aq) —> Pb(OH)2 (s)
what is the observation of the reaction of lead with excess NaOH? equation?
- the white ppt redissolves to form the tetrahydroxoplumbate (II) ion
Pb(OH)2 (s) + 2OH- (aq) —> [Pb(OH)4] 2- (aq)
what is the observation of the reaction of lead with HCl?
- dense/heavy white ppt of lead chloride formed
Pb2+ (aq) + 2Cl- (aq) —> PbCl2 (s)
what is the observation of the reaction of lead with KI?
- dense bright yellow precipitate of lead (II) iodide is formed
Pb2+ (aq) + 2I- (aq) —> PbI2 (s)
USED IN INDENTIFYING Pb2+ IONS
the oxidising power of halogens (increases/decreases) down the group?
decreases
(can be shown by electrode potentials. the more positive the standard electrode potential, the greater the oxidising power:
Cl2 + 2e- ⇌ 2Cl- Eθ/volts = +1.35
Br = +1.09
I = +0.54)
chlorine has a (greater/lower) oxidising power than bromine. this means that chlorine will displace bromine from a solution of bromine ions
greater
(solution will change colour to orange)
the value for the standard electrode potential of (iodine/chlorine/bromine) is the least positive?
iodine / iodide
this means its easier to oxidise iodide than it is to oxidise chloride or bromide ions
since oxidising power of halogens decreases down group 7, their reactions with conc sulfuric acid, which is also strong oxidising agent, will show gradual change going down group
all the halide ions chloride, bromide and iodide are oxidised by sulfuric acid
can sodium chloride NaCl be oxidised by sulfuric acid? why?
- steady fumes of HCl gas produced, but CANNOT be oxidised by sulfuric acid
- bc the sulfuric acid has a less positive electrode potential than the Cl2/2Cl-
- no further reaction takes place
NaCl(s) + H2SO4 (c) —> NaHSO4 (s) + HCl(g)
can sodium bromide NaBr be oxidised by sulfuric acid? why?
- at first steady fumed of HBr gas is produced:
NaBr(s) + H2SO4 (c) —> NaHSO4 (s) + HBr (g) - but as bromide ion CAN be oxidised by sulfuric acid, a redox reaction then takes place producing bubbles of colourless gas and orange fumes of bromine Br2
2HBr (s) + H2SO4 (c) —> SO2 + Br (g) + HBr (g)
can sodium iodide NaI be oxidised by sulfuric acid? why?
- at first steady fumes of HI produced
NaI (s) + H2SO4 (c) —> NaHSO4 (s) + HI (g) - but as iodide ions CAN be oxidised by sulfuric acid, it reacts further in a redox reaction to produce purple I2 fumes which can sublime into a black/brown solid or solution
2HI (s) + H2SO4 (c) —> SO2 + I2 (g) + 2H2O (g) - since iodide an even stronger reducing agent, further reduction of H2SO4 can also occur producing yellow solid of sulfur, and may be smell of rotten eggs from H2S
if cold dilute sodium hydroxide used in reaction between chlorine and sodium hydroxide, what happens?
- disporportionation reaction occurs (chlorine both oxidised and reduced)
Cl2 (g) + 2NaOH (aq) —> NaCl (aq) + NaOCl (aq) + H2O (l)
if heated concentrated sodium hydroxide used in reaction between chlorine and sodium hydroxide, what happens?
- another disproportionation reaction occurs
- but sodium chloride and sodium chlorate (V) are formed
3Cl2 (g) + 6NaOH (aq) —> 5NaCl + NaClO3 (aq) + 3H2O (l)
what is the oxidation state of chlorine in Cl2?
0
what is the oxidation state of chlorine in sodium chloride?
-1
what is the oxidation state of chlorine in sodium chlorate (V), NaClO3?
+5
what colour are iodine fumes?
purple
what colour are bromine fumes?
orange
what is the reason that chlorine and chlorate ions (ClO3 -)can be used as bleach and can kill bacteria?
bc of the oxidising power of chlorine and chlorate ions
- chlorine is used as disinfectant in water supplies as the microbe cells (bacteria) are oxidised
what is the use of sodium chlorate (I)?
used for bleach
(made by reaction with cold dilute sodium hydroxide)
what is the use of sodium chlorate (V)?
used for weed killer
what type of reaction is bleaching?
an oxidation reaction
write the equation for the reaction of hot concentrated aqueous sodium hydroxide with chlorine? [1]
6NaOH + 3Cl2 —> NaClO3 + 5NaCl + 3H2O
what is meant by the term disproportionation?
- where the same element is both oxidised and reduced
carbon is the first element in group 4. two of its allotropes are diamond and graphite. a compound that forms structures corresponding to diamond and graphite is boron nitrite.
describe the structure of graphite and explain why hexagonal boron nitride can adopt the same structure yet have different electrical conductivity properties [5 QER]
- each C atom covalently bonded to three other C atoms forming layers
- layers held together by weak intermolecular forces
- BN is isoelectronic with C so it forms similar structures
- graphite conducts electricity since electrons are delocalised but in BN, each N has a full unbonded p-orbital and each B has an empty unbonded p-orbital so it doesn’t conduct electricity
(accept electrons are no delocalised in BN so it doesn’t conduct electricity)
state one use for the cubic boron nitride structure [1]
- wear-resistant coatings
- catalyst suppirt
- for mounting high power electronic components
- drills in industry
- cutting instruments
what is the chemical equation for the reaction between aluminium oxide and sulfuric acid?
Al2O3 + 3H2SO4 —> Al2(SO4)3 + 3H2O
describe how the stability of oxidation states changes down group 3?
- the stability of the +1 oxidation state increases down the group
- while the stability of the +3 oxidation state reduces down the group
describe the structure and bonding in Al2Cl6:
- aluminium hexachloride (Al2Cl6)
- is a donor-acceptor dimer
- made of two separate, identical molecules which are linked together by two coordinate bonds
- two atoms of chlorine share their lone pair of electrons with two atoms of aluminium to form the coordinate bonds
describe the structure and bonding in NH3BF3:
- NH3BF3 is a donor-acceptor compound
- there is a coordinate bond formed between the nitrogen and boron atoms, where nitrogen supplies both the electrons for the bond
explain which boron nitride structure is suitable to be used as a lubricant:
- the hexagonal boron nitride structure
- has weak intermolecular forces between the layers
- and so these layers can slide, making it suitable to be used as a lubricant
identify the reducing agent in the following reaction:
CuO + CO —> Cu + CO2
Cu: 2+ —> 0 (reduced)
C: 2+ —> 4+ (oxidised)
the reducing agent is carbon monoxide
does PbCl2 react with water?
- no
- but is partially soluble in cold water and more soluble in hot water
what is the chemical equation for the reaction of SiCl4 with water?
SiCl4 + 2H2O —> SiO2 + 4HCl
what is the chemical equation for the disproportionation reaction that chlorine undergoes with water?
Cl2 + H2O ⇌ 2H+ + Cl- + ClO-
why are chlorine and chlorate ions used in water treatment?
- they kill bacteria which makes the water safe
- this is a result of their oxidising power
isoelectronic definition
having the same number of e- or same electronic structure
BN vs C = 12e-
