✅3.3: Chemistry Of The P Block Flashcards
What makes an element a p block element?
An element is a p block element if their outer electrons are located in p sub shells
What does every p block element have?
A full s sub-shell in their outer shell with between 1-6 further electrons in their p sub shell
Give an example of the electronic configuration of group 3,4,5 and 6 p block elements
Group 3= s2p1
Group 4= s2p2
Group 5= s2p3
Group 6= s2p4
What is the maximum oxidation states a p-block element can have?
The oxidation state that is equal to their group number e.g C has a maximum oxidation state of 4
What is the other common oxidation state of a p block element
Two less than the group number e.g C has an oxidation state of +2 and +4
What is the trend in oxidation states of p block elements as you descend the group
As you descend a group, the most stable oxidation state of an element decreases:
E.g in group 4 most stable oxidation state of Sn = 4 whereas oxidation state of Pb=2
Define the inert pair effect
The tendency of the s2 pair of electrons in an atom to stay paired leading to a Lower oxidation state
Define octet expansion
The ability of some atoms to use d-orbitals to have more than 8 electrons in their valence shell
What does the phrase “when a group 4 element has an oxidation state of 4, it involves all 4 electrons” mean?
It means that one electron from the S sub-shell has been promoted to the p sub-shell, allowing a maximum of 4 covalent bonds to form
What does the phrase “when a group 4 element has the oxidation state of +2, the inner two electrons do not become involved” mean?
The energy required to unpair the S orbitals > the energy released by making 2 extra bonds and :: not energetically favourable, making the lower oxidation state more stable
What is the inert pair?
The inner two electrons (s2) that do NOT become involved (not unpaired and then promoted) allowing a more stable lower oxidation state
Where does the trend of ns2 electrons to become an inert pair occur in the periodic table?
Group 3,4 and 5
What is the maximum number of outer shell electrons that can surround the atoms in the elements in the first members of each group (2nd period and above?)
8 -four pairs of electrons
Describe basic bonding in B, C, N, O2
Boron: 3 covalent bonds and is electron deficient (explaining why it makes co-ordinate bonds)
Carbon: 4 covalent bonds
Nitrogen: 3 covalent cons and 1 lone pair
Oxygen: 2 covalent bonds and 2 lone pairs
Why can elements in the p block period 3 and below expand their octet?
They have access to d-orbitals that are not present in the second shell :: every electron in the outer shell can be used to form a covalent bond as there’s no longer a limit of 8 electrons in the outer shell.
What groups are affected by the possibility of expanding the octet?
Groups 5.6 and 7
E.g: phosphorus can form 5 covalent bonds (PCl5)
Sulfur can for 6 covalent bonds (SF6)
Chlorine can form up to 7 covalent bonds (ClO4-)
Why does the effect of the inert pair effect become stronger down the group?
1) The unpairing energy must come from the energy released when bonds are formed
2) As you go down the group the bonds get weaker, so less energy is released as they form.
3) For The lowest members of the group the energy released by making extra bonds is not enough to balance the energy needed to move an electron from the s to p sub shell
Describe the p-block elements at the top and bottom.
Top= non metals such as B, C or N Bottom= metals such as Tl, Pb or Bi
Describe why there’s a change in non metallic to metallic properties as you decrease down the p block
1) Ionisation energy decreased on going down a group so it’s easier for the atoms to form positive ions.
2) This allows some atoms to contribute to form ionic bonds with non metals
3) This also helps elements form metallic bonds as the atoms form positive ions and a sea of delocalised electrons easily
Define the term Amphoteric
Amphoteric materials react with both acids and bases
Define an acid
a molecule which can donate a proton or accept an electron pair in reactions
Define a base
A molecule that can accept a hydrogen ion (H+) from another substance
What do amphoteric oxides show?
They show both acidic and basic properties (normally close to the line separating metals and non metals)
How would you show that a substance (metal oxide) is amphoteric?
Show it reacting with an acid e.g HCL and a base e.g NaCl
Name 2 amphoteric oxides
Aluminium oxide: Al2O3 + 6HCL —> 2AlCl3 + 3H2O Al2O3 + 2NaOH + 3H2O —> 2Na[Al(OH)4] Lead (||) oxide: PbO + 2HNO3 —> Pb(NO3)2 + H2O PbO + 2NaOH + H2O —> Na2[Pb(OH)4]
What happens when solutions containing amphoteric metal compounds react with NaOH?
They first form a metal hydroxide precipitate
The metal hydroxide precipitate then reacts with excess sodium hydroxide meaning the precipitates redissolve
Give an example of the equation when Al3+ (amphoteric metal oxide) reacts with hydroxide
1) Al3+ +3OH- —> Al(OH)3 (s)
2) Al(OH)3 + OH- —> [Al(OH)4]- (aq)
Group 3 chemistry:
What are the two most common elements in group 3?
Boron and aluminium
Group 3 chemistry:
Name one difference in the physical properties between boron and aluminium
Boron = non metal aluminium = metal
Group 3 chemistry:
Define an electron deficient atom
An atom that does not have a full outer shell I.e has fewer than 8 electrons in its outer shell
Group 3 chemistry:
What bonds do group 3 compounds usually form?
Normally the 3 group 3 electrons form form 3 covalent bonds with halogens E.g BF3, leaving the outer shell with only 6 electrons (lone pair deficient)
Group 3 chemistry:
What do the group 3 compounds do to fill their deficient outer shell?
What does this make them?
The atoms e.g BF3 will form co-ordinate bonds to gain electron pairs
This makes them ELECTRON ACCEPTORS
Group 3 chemistry:
Name a couple specific methods group three compounds fill their outer shell?
React with other compounds or through forming dimers (see diagram pg 31 of textbook)
Group 3 chemistry:
Give an example of the formation of a dimer
AlCl3 + AlCl3 —> 2AlCl6
In this process each electron deficient aluminium atom uses a lone pair on a chlorine atom to form a co-ordinate bond.
Group 3 chemistry:
What is a donor acceptor compound?
Where one molecule donates a lone pair of electrons and the other accepts it e.g seen between the electron deficient BF3 and the lone pair on NH3.
Group 3 chemistry:
List some similarities between the B-N bond and the C-C bond
- total of 12 electrons on the two atoms
- atomic radii of boron nitride and CC similar
- similar relationship in electronegativities
Group 3 chemistry:
What are the two structures of boron nitride?
(A) hexagonal boron nitride
(B) cubic boron nitride
Group 3 chemistry:
Basically describe hexagonal boron nitride
Layers where nitrogen and boron atoms are combined in a hexagonal network (similar structure to graphite)
Group 3 chemistry:
Basically describe cubic boron nitride
Boron and nitrogen atoms combine three dimensionally replacing carbon atoms in diamond
Group 3 chemistry:
Describe one difference between hexagonal boron nitride and graphite
difference: The atoms in different layers lie directly above/below one another (boron sandwiched between 2 nitrogen atoms)
In graphite the atoms on adjoining layers are NOT directly above one another
There are no delocalised electrons present in boron nitride with electrons localised as lone pairs on nitrogen atoms :: hexagonal boron nitride can’t conduct electricity
Group 3 chemistry:
Describe one similarity between hexagonal boron nitride and graphite
The intermolecular forces between layers of boron nitride are weak so it shares the ability with graphite for layers to slip over one another :: can be used as a lubricant
Group 3 chemistry:
Why is hexagonal boron nitride an insulator?
The B-N bonds are polar due to a difference in electronegativity of the two atoms.
Group 3 chemistry:
Name some uses for hexagonal boron nitride
Substrate for semiconductors Microwave transport windows Structural materials for seals Electrodes Catalyst carriers in fuel cells and batteries
Group 3 chemistry:
Name some similarities between cubic boron nitride and diamond
Extremely hard with a high melting point as covalent bonds must be broken to melt/break solid
Group 3 chemistry:
Name some uses of cubic boron nitride
Wear-resistant coating
Industrial abrasive
Group 4 chemistry:
What is the first group 4 element and what is it’s oxidation state?
Mental/non metal?
First element = carbon
Oxidation state = +4 (only +2 in CO)
Non metal Generally forming covalent bonds
Group 4 chemistry:
What is the largest group 4 element?
Most stable oxidation state?
Metal/non metal?
Element: Lead (Pb)
Oxidation state = +2 (only +4 in PbO2)
Metal generally forming ionic bonds
Group 4 chemistry:
What is the most stable from of Carbon?
What is the least stable form of carbon?
CO2
CO
Group 4 chemistry:
What type of agent will CO act as and why?
Give an example of when this agent is used
Act as a reducing agent as it’s easily oxidised from +2 to +4
Reducing agent used for extracting metals from their oxides
Group 4 chemistry:
Give the reaction of Iron (|||) oxide and Copper oxide with CO, showing its role as a reducing agent
Fe2O3 (s) + 3CO (g) —> 2Fe (s) + 3CO 2 (g)
CuO (s) + CO (g) —> Cu (s) + CO2 (g)
Group 4 chemistry:
When can using CO as a reducing agent for extracting metals from their oxides not be used
It can’t be used if the oxides are of more reactive metals (anything above zinc in the reactivity series) as they are too stable so won’t react
Group 4 chemistry:
What is the most stable oxide of lead?
What is the least stable oxide of lead?
Lead (||) oxide PbO
Lead (|V) oxide PbO2
Group 4 chemistry:
What form of agent does PBO2 become?
It’s a good oxidising agent as it become easily reduced from +4 to +2
Group 4 chemistry:
What are all Pb(|V) compounds?
All oxidising agents
Group 4 chemistry:
What is the equation showing the purpose of PbO2?
PbO2 + 4HCL (conc) —> PbCl2 + Cl2(g) + 2H2O (l)
Group 4 chemistry:
How should you prove an oxide is acidic?
How do you prove an oxide is basic?
Need to show it reacting with a base
Need to show it reacting with an acid
Group 4 chemistry:
Describe the oxides of carbon dioxide and silicon dioxide
Acidic
Group 4 chemistry:
Describe the oxides of geranium, tin and lead
Amphoteric
Group 4 chemistry:
What is the general classification of oxides in group 4
Metal oxides are basic oxides
Non metal oxides are acidic oxides
Group 4 chemistry:
What is carbon dioxide?
A colourless gas made up of small covalent molecules, it’s an acidic oxide as it’s soluble in water to give an acid
CO2 + H2O —> H+(aq) + HCO3-
Group 4 chemistry:
Name a characteristic property of all acidic oxides and show this in an equation
All acidic oxides react with alkalis to form a salt.
CO2 (g) + 2NaOH (aq) —> Na2CO3 (aq) + H2O (l)
With CO2 this always produces a carbonate or hydrocarbonate salt
Group 4 chemistry:
What is lead (||) oxide
An orange solid
An amphoteric oxide :: it reacts with acids and bases
Group 4 chemistry:
Show PbO amphoteric nature in 2 equations
Acting as a base
PbO + 2HNO3 —> Pb(NO3)2 (aq) + H2O (l)
Acting as an Acid
PbO + 2NaOH + H2O —> Na2[Pb(OH)4] (aq)
Group 4 chemistry:
What are the stable chlorides of carbon and silicon?
Tetrachlorides CCl4 and SiCl4, both colourless liquids containing individual covalent molecules
Group 4 chemistry:
Why are CCl4 and SiCl4 tetrahedral?
Because they both contain 8 electrons in the valence shell
For instance CCl4 electronic configuration = 2 6
2s 2p
4 carbon electrons and 4 chlorine electrons
Group 4 chemistry:
How does CCl4 react with water?
Does NOT react with water
Forms a separate layer under the water
The carbon atom can’t combine easily with water molecules
Group 4 chemistry:
Why doesn’t CCl4 react readily with water
The absence of available d orbitals in the valence shell means that the octet can’t be expanded to allow the water molecule to combine with the carbon atom
Group 4 chemistry:
How does SiCl4 react with water?
Reacts quickly with water in a hydrolysis reaction.
Produces fumes of hydrogen chloride gas and silicon dioxide SiO2 as a solid ppt.
Group 4 chemistry:
Describe the trend of reactivity with water as you descend group 4
The reaction becomes more vigorous down the group as the bonds in the compound become weaker
SiCl4 + 2H2O —> SiO2 + 4HCL
Or
SiCl4 + 4H2O —> Si(OH)4 + 4HCL
Group 4 chemistry:
What’s the reason behind silicons increased reactivity with water
Silicon can access 3d orbitals in addition to 3s and 3p orbitals involves in the bonding to chlorine atoms. The lone pairs of the water can from co ordinate bonds with these empty d orbitals
Group 4 chemistry:
What is the most stable chloride of lead?
Describe this
Lead (||) chloride White ionic solid made up of Pb2+ and Cl- ions Does not react with water as it’s ionic Does not dissolve in cold water Does dissolve in hot water
Group 4 chemistry:
What are all lead compounds generally?
Bar which 2 compounds does this apply to?
Generally insoluble in cold water.
Apart from lead nitrate Pb(NO3)2 and lead ethanoate Pb(Ch3COO)2.
Group 4 chemistry:
What happens if you add NaOH (aq) to Pb2+ (aq)
Name the Anion present
Anion present: OH-
Observation: initial white precipitate of Pb(OH)2 is formed
Pb2+ (aq) + 2OH- (aq) —> Pb(OH)2 (s)
Group 4 chemistry:
What happens if you add excess NaOH (aq) to Pb2+ (aq)
Name the Anion present
Anion present: OH-
The white precipitate from when adding initial NaOH to Pb2+ redissolves in excess OH- to form tetrahydroxoplumbate ion
Pb(OH)2 + 2OH- —> [Pb(OH)4]2-
Group 4 chemistry:
What happens if you add HCL (aq) to Pb2+ (aq)
Name the Anion present
Anion present: Cl- (aq)
A dense white ppt of lead chloride forms
Pb2+(aq) +2Cl- —> PbCl2 (s)
Group 4 chemistry:
What happens if you add KI to Pb2+ (aq)
Name the Anion present
Anion present: I- (aq)
A dense bright yellow ppt of lead iodide, PbI2 is formed
Pb2+ (aq) + 2I- (aq) —> PbI2 (s)
Group 4 chemistry:
What are the two compounds that produce a yellow ppt and describe their yellow ppt
1) silver iodide- pale yellow ppt
2) Lead iodide- bright/canary yellow
Group 7 chemistry:
group 7 elements metals/non metals?
All elements are non metals
Group 7 chemistry:
Describe the trend in oxidising agent power as you descend as you descend the group.
Oxidising agent power decreases down the group, as the E value decreases :: Cl2 is easiest to reduce
Group 7 chemistry:
Why does the power of group 7 oxidising agents decrease down the group
As the E value of chlorine is most positive, it readily gains electrons to form chloride ions
Cl2(g) + 2e- —> 2Cl-
As the E value of iodine us least positive, it gains electrons less readily than bromine and chlorine.
I2(s) + 2e- —> 2I- (aq)
(This also shows it’s easier to oxidise iodide ions than bromide or chloride ions)
Group 7 chemistry:
What is a halogen?
What is a halide?
Halogen is a positive ion such as I+
Halide is a negative ion such as I-
Group 7 chemistry:
What is the expected result if you were to bubble chlorine gas into a solution containing bromide ions?
The solution would go orange showing that bromine is being formed
Cl2(g) + 2Br- —> Br2(aq) + 2Cl- (aq)
Group 7 chemistry:
Explain the expected result if you were to bubble chlorine gas into a solution containing bromide ions?
Cl2(g) + 2Br- (aq) —> Br2 (aq) + 2Cl- (aq)
The orange solution occurs as chlorine is a stronger oxidising agent than bromine (more positive E value( meaning chlorine is able to oxidise bromide to for bromine molecules.
Group 7 chemistry:
Describe concentrated sulfuric acid
Concentrated sulfuric acid is a strong acid and an oxidising agent
Group 7 chemistry:
Describe what happens when concentrated sulfuric acid is added to sodium chloride (NaCl)
NaCl(s) + H2SO4 —> NaHSO4 (s) + HCL (g)
Observation:
1) steamy fumes of HCL
The HCL is difficult to oxidise (E=1.36V) and :: sulfuric acid doesn’t cause redox reaction
Group 7 chemistry:
Describe what happens when concentrated sulfuric acid is added to sodium bromide (2)
NaBr(s) + H2SO4 —> NaHSO4(s) + HBr (g)
Observation:
1) Steamy fumes of HBr
2)Orange fumes of Br2
Group 7 chemistry:
Explain the observation when concentrated sulfuric acid is added to sodium bromide
Sulfuric acid oxidises some of the HBr to to brown fumes of Br2 and So2 gas.
This is because hydrobromic acid is slightly easier to oxidise (E= 1.09V) so the sulfuric acid causes the redox reaction:
2HBr (s) + H2SO4 —> SO2 (g) + Br2 (g) + 2H2O (l)
Sulfur is reduced from +6 to +4
Bromine is oxidised from -1 to 0
Group 7 chemistry:
Describe what happens when concentrated sulfuric acid is initially added to sodium iodide
Initially HI (g) is produced
NaI (s) + H2SO4 —> NaHSO4 + HI(g)
Initial observation: Steamy fumes of HI
Group 7 chemistry:
Describe what happens when concentrated sulfuric acid is added to NaI after oxidation
Sulfuric acid easily oxidised the HI(g) with E=0.54V into mixture of I2(s), SO2 (g) and H2S (g)
2HI(s) + H2SO4 —> SO2(g) + I2 (s) + 2H2O (l)
S is reduced from +6 to +4
I is oxidised from -1 to 0
Group 7 chemistry:
State all possible observations when concentrated sulfuric acid is added to sodium iodide (5)
1) steamy fumes of HI
2) purple fumes of I2
3) black solid/brown solution (I2)
4) smell of rotten eggs (H2S)
5) Yellow solid (S)
Group 7 chemistry:
Why can further reduction of sulfuric acid occur with HI?
Further reduction of H2SO4 to S and H2S can occur as the HI is a better reducing agent (least positive E value) than HBr or HCl
Group 7 chemistry:
What is the maximum possible oxidation state of a group 7 element, give an example, explain what happens to such compounds
- Compound e.g ClO4- can have halogens with a +7 oxidation state.
- These ions can be very unstable and many shock sensitive
- They decompose explosively to form compounds with the chlorine in a less positive oxidation state
Group 7 chemistry:
What are the most common oxidation states of group 7 atoms?
1) -1 as halide ions e.g I-
2) 0 in the element e.g I2 (g)
3) +1 as a halogen e.g I+
4) +5
Group 7 chemistry:
Describe the trend in oxidation states in group 7
Higher oxidation states become more stable as you go down the group e.g Fluoring can’t acces high oxidation states but all other members can form compounds with oxidation states up to +5 (with very electronegative elements like oxygen or fluorine)
Group 7 chemistry:
How are the ClO- ion and ClO3- ion formed?
Ions are formed by reaction of the elements with an alkali
Group 7 chemistry:
What happens when chlorine is bubbles through water?
Reversible reaction occurs: Cl2(g) + H2O —> HCl(aq) + HOCl (aq)
Chlorine is being both oxidised and reduced e.g oxidation state in Cl2 =0, HCl =-1 and HOCl =+1 in HOCl.
1st disproportionation reaction
Group 7 chemistry:
What is a disproportionation reaction?
A reaction where the same element end up in two different compounds, one with a higher oxidation state (oxidised) and one with a lower oxidation state (reduced)
Group 7 chemistry:
What happens when NaOH is added to chlorine
Equilibrium reaction:
The products are both acids :: the addition of alkali instead of water will shift the equilibrium to the RHS of the new equation:
Cl2(g) + 2OH- —> Cl- + OCl- + H2O
(2nd disproportionation equation)
Group 7 chemistry:
What happens when Cl2 is heated with concentrated sodium hydroxide?
ClO- ion is stable at room temperature but not on heating.
3Cl2 (g) + 6OH- —> 5Cl- + ClO3- + 3H2O
(3rd disproportionation equation)
This gives chlorate (V) ion where chlorine is in +5 oxidation state
Group 7 chemistry:
Are the ions (Cl-, ClO3-) oxidising or reducing agents, give an example
They are oxidising agents:
E.g ClO- + 2H+ + 2e- —> Cl- + H2O
Group 7 chemistry:
Is elemental chlorine an oxidising or reducing agent?
It is an oxidising agent:
E.g Cl2 + 2e- —> 2Cl-
Group 7 chemistry:
Name some uses of chlorine and chlorate ions
The oxidising power is the basis of their use in bleaches, as material is oxidised to become colourless
The oxidising ability of ClO3- allows it to kill bacteria, as the microbe cells are oxidised. This is the basis of chlorination of water supplies to disinfect them.
