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A2 Chemistry > 3.3 P-Block > Flashcards

3.3 P-Block Flashcards

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1
Q

How many oxidation states do p-block elements usually have?

A

Two. The maximum oxidation state which is the group number and a lower oxidation state which is two less

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2
Q

Draw out the table for the oxidation states of groups 3,4,5

A
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3
Q

What is the inert pair effect?

A

The tendency of the S2 pair of electrons in an atom to stay paired leading to a lower oxidation state

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4
Q

In which groups does the inert pair effect occur? What is the trend of these groups?

A
    1. 3,4,5. Effect increases as you go down group due to the poor sheilding effect of the d and f orbital electrons.
    1. The electrons present in the intervening d- (and f-) orbitals do not effectively shield the s-electrons of the valence shell down the group. As a result, the inert pair of ns electrons remains more tightly held by the nucleus and hence participates less in bond formation .
    1. The inert-pair effect is caused by the increasing energy difference between s and p electrons as atoms get larger within families. As the s-p energy difference grows, it becomes harder to bring the s-electrons into play when forming bonds.
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5
Q

What is octet expansion?

A

the ability of some atoms (third period and below) to use available d-orbitals to have more than 8 electrons in their valence shell

For example, phosphorus can use all outer shell electrons to form coordinate bonds as valance electron numbers are no longer limited to 8. e.g. PCl5

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6
Q

What is meant by amphoteric?

A

Materials react with both acids and bases

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7
Q

What type of oxides do p-block elements form?

A

Amphoteric oxides, and these are typically metals close to the line separating metals and non-metals.

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8
Q

When is a precipitate formed?

A

When solutions containing amphoteric metal compounds react with sodium hydroxide, metal hydroxide precipitates are formed. Since the hydroxides can react more with sodium hydroxide, these precipitates will then redissolve

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9
Q

What is special about aluminium?

A

It is a metal but highly electronegative so some of its compounds are covalent and show similarities to compounds of boron (element above Al in group 3 and non-metal)

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10
Q

What is an electron deficient atom?

A

one that does not have a full outer shell e.g. fewer than 8 electrons in its outer shell

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11
Q

How many covalent bonds do group 3 elements form? What is the name of this compound?

A

They usually form 3 bonds (e.g. AlCl3), so to fill their outer shell they will often form coordinate bonds with other compounds. They are electron acceptors.

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12
Q

What is the name of other molecules (not necessarily group 3) that can form coordinate bonds to remove their electron deficiency?

A

donor-acceptor compounds. One molecule donates a lone pair (e.g. nitrogen) and the other accepts it (e.g. boron)

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13
Q

What are the similarities between the BN and the CC bond?

A
  • total of 12 electrons between the two atoms
  • similar atomic radii (carbon is almost exactly the average of boron and nitrogen)
  • electronegativity of carbon lies midway between boron and nitrogen
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14
Q

What is hexagonal boron nitride?

A
  • similar hexagonal sheets to those found in graphite
  • in this case atoms in different layers lie directly above one another with each boron having a nitrogen atom directly below it (this differs from graphite as the layers are arranged so that atoms on adjoining layers are not directly above one another)
  • weak forces between layers so BN layers can slip over eachother making it soft so can be used as a lubricant
  • no delocalised electrons present but electrons localised as lone pairs on nitrogen
  • B-N bonds are polar due to differences in electronegativities.
  • This makes BN an insulator and leads to its use in electronics as a substrate for semi-conductors
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15
Q

What is cubic boron nitride?

A
  • like diamond cubic boron nitride is extremely hard with a high melting point as covalent bonds must be broken to break or melt the solid
  • this leads to its use as wear-resistant coating or an industrial abrasive
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16
Q

What are top and botton of group 4?

A

Carbon and lead

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17
Q

What is the most stable oxidation state for the group 4 elements?

A

Most stable for all is +4 except lead where +2 is most stable. The stability of the +2 oxidation state increases down the group, however only lead has +2 as the most stable

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18
Q

Why does CO act as a reducing agent?

A

It becomes easily oxidised from +2 to +4.

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19
Q

What is CO used for?

A

extracting less reactive metals (anything below zinc in the reactivity series) from their oxides

20
Q

Why are all lead (IV) compounds oxidising agents? What is the most stable lead oxide?

A

They are easily reduced from an oxidation state of +4 to +2. PbO is the most stable oxide of lead.

21
Q

Metal oxides and non-metal oxides, are they basic or acidic?

A

Metal oxides= basic
non-metal oxides= acidic

This is reflected in group 4 as it changes from non-metals to metals. CO2 is acidic whereas PbO is amphoteric

22
Q

What happens when you react CO2 with alkalis?

A

Salt is formed. All salts produced in this way are carbonates or hydrogen carbonates

23
Q

What colour and state is lead (II) oxide?

A

orange solid, bonding is mainly ionic

24
Q

why is lead (II) oxide an amphoteric oxide?

A

reacts with acids and bases. If its reacting with a base it also needs water as a reactant. In both cases lead changes to the oxidation state of +4. Example of a compound of lead from reaction with sodium hydroxide is Na2[Pb(OH)4]

25
Q

Which two elements from group 4 form stable tetrchlorides?

A

carbon and silicon. Both colourless liquids with tetrahedral molecules with full outer shells

26
Q

Why does CCl4 not react with water?

A

absence of d-orbitals in the valence shell means it cannot undergo octet expansion to allow the water molecules to combine with the carbon atoms

27
Q

What happens when silicon tetrachloride reacts with water?

A
  • rapid hydrolysis reaction
  • produces fumes of HCl and SiO2 as a precipitate
  • reason: silicon possess available 3d-orbitals in addition to the 3S/P involved in bonding to chlorine atoms. The lone pairs of water can form coordinate bonds to empty d orbitals, giving a complex intermediate wthat eliminates two HCl molecules to give Si(OH)2Cl2.
  • This molecule can then eliminate two more molecules of HCl to leave SiO2

reaction becomes more vigorous down the group as the bonds in the compounds become weaker

28
Q

What is the equation for the overal reaction of silicon tetracloride with water?

A

SiCl4 (l) +4H2O (l) –> Si(OH)4 (s) + 4HCl (g)

29
Q

What colour and state is lead (ii) chloride?

A

white ionic solid made up of Pb2+ and Cl- ions.

30
Q

Can lead (ii) chloride react with water?

A

No it is an ionic compound. It can be dissolved in hot water but not in cold

31
Q

What are the only lead (II) compounds that dissolve readily in cold water?

A

lead nitrate and lead ethanoate

32
Q

How would you form a white precipitate of Pb(OH)2?

Using a solution of lead nitrate or lead ethanoate as a source of Pb2+

A

add aqueous sodium hydroxide.

If you add this in excess the precipitate redissolves to form [Pb(OH)4]2-

33
Q

How do you form lead chloride? what colour and state is this?

Using a solution of lead nitrate or lead ethanoate as a source of Pb2+

A

Add HCl. lead chloride is a dense white precipitate

34
Q

How do you form PbI2? What colour and state is this?

Using a solution of lead nitrate or lead ethanoate as a source of Pb2+

A

Add KI. PbI2 is a bright (canary) yellow precipitate.

35
Q

What is the trend in halogens?

A

Oxidising power decreases down the group

36
Q

How do you form a hydrogen halide? What state are these?

A

react concentrated sulphuric acid with sodium halides. Hydrogen halides all appear as steamy gasses

37
Q

How does concetrated sulfuric acid react as an oxidising agent?

A

it can oxidise the lower halides but not chloride.

38
Q

What happens when you add concentrates H2SO4 to NaCl?

A

HCl gas produced. But as HCl is difficult to oxidise no redox reaction occurs.

NaCl (s) + H2SO4 –> NaHSO4 (s) + HCl (g)

39
Q

What happens when you add concentrates H2SO4 to NaBr?

A

Observation: steamy fumes of HBr and orange fums of Br2
Initial reaction produces HBr gas. Sulfuric acid then oxidises some of the HBr to form brown fumes of Br2 and SO2 gas. Redox reaction occurs.
2HBr (S) + H2SO4 (conc) –> Br2 +2H2O

40
Q

What happens when you add concentrates H2SO4 to NaI?

A
  • Initially produces HI gas
  • oxidises HI(S) further to produce SO2(g), I2 (S), H2O(l)
  • further reduction of the sulfuric acid to S and H2S can occut as HI is a better reducing agent than the other hydrogen halides
  • Observations: steamy fumes of HI, purple fumes of I2 or brown/black solid solution, smell of rotten eggs (H2S), yellow solid (S)
41
Q

What is disproportionation? What is an example of a disproportionation reaction?

A

Same element oxidised and reduced. Example, chlorine bubbled through water sets up a reversible reaction with HCl and Hydrogen chlorate (HOCl)

42
Q

What is the trend for higher oxidation states (+1 to +5) of halides as you go down the group?

A

they become more stable

43
Q

How do you form OCl-?

A

bubble chlorine gas through alkaline sodium hydroxide at room temperature

44
Q

How do you form ClO3-?

A

heat concentrated sodium hydroxide and chlorine gas. The products are 5Cl-, 3H2O and ClO3-

45
Q

What are the similarities between ClO- and Cl2?

A

They are both oxidising agents. This leads to its ability to kill bacteria as the microbe cells are oxidised and this is the basis of chlorination of water supplies to disinfect them

46
Q

Why does aluminium (a metal) show similarities to analogous compounds of boron (non-metal)?

A

Aluminium has a high electronegativity so some of its compounds are covalent

47
Q

What are electron acceptors?

A

Form coordinate bonds to gain electron pairs to fill their outer shells

A2 Chemistry (3 decks)

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