Unit 3.3 - Chemistry of the p-block Flashcards
Periodicity
How properties change across the periodic table
Name 2 compound with more than 8 electrons in their outer shell
Phosphorus (V) chloride —> PCL5
Phosphorus (V) fluoride —> PF5
What can we notice about the phosphorus compounds PCL5 and PF5?
There are 10 electrons around the central phosphorus atom
What’s the name for having more than 8 electrons in an outer shell?
Expanding the octet
Which elements are the only ones which can expand their octets?
Fluorine
Oxygen
Chlorine
What can fluorine, oxygen and chlorine expand their octets with?
Highly electronegative elements
Why are fluorine, oxygen and chlorine able to expand their octets?
They have large electronegativity values and have a very strong tendency to attract electrons to themselves
What does Florine, oxygen and chlorine expanding their octets occur with?
Elements in the 3rd row of the periodic table (Na —> Ar)
What does fluorine, oxygen and chlorine expanding their octets NOT occur with?
The elements in the 2nd row of the periodic table (Li—>Ne)
Why are fluorine, oxygen and chlorine able to expand their octets with the elements in the 3rd row of the periodic table?
As the elements in the 3rd row can expand their octet of electron as vacant 3d orbitals of suitable energy are available for bonding, allowing them to hybridise
How come Florine, oxygen and chlorine are able to expand their octet with elements from the 3rd row of the periodic table but not the second?
The energy difference between the 3s, 3p and 3d orbitals are small enough to overcome when bonding to strongly electronegative elements
With the 2nd row elements, the energy difference is too large to be overcome and no orbitals are available for expanding the octet
What happens to the gap between subshells as you get further from the nucleus?
Decreases
What does a smaller gap between subshells lead to?
Smaller energy differences
What can happen to small energy differences?
Can be overcome when bonding to strongly electronegative elements
Valency
Amount of bonds they can form
Maximum valency of second row elements
4 pairs
Maximum valency of 3rd row elements
Up to 7 pairs
Octet expansion
The ability of some atoms to use d-orbitals to have more than 8 electrons in their valence shell
Which orbitals are used to expand octets?
d-orbitals
What is the maximum covalent bonds that can be formed by boron?
3 (this is electron deficient)
What is the maximum covalent bonds that can be formed by carbon?
4
What is the maximum covalent bonds that can be formed by nitrogen
3 (this is also has 1 lone pairs)
What is the maximum covalent bonds that can be formed by oxygen?
2 (this is also has 2 lone pairs)
What type of orbitals do elements in period 3 and below have and why is this important?
d orbitals
More bonds can be formed
How is PF5 formed?
An s-electron is promoted to a d-orbital
These then hybridise forming 5 sp^3d orbitals (each having the same energy)
Trends in bonding across the p-block
Ionic to covalent
Trend in bonding down the p-block
Bonding becomes more ionic (metallic)
Metallic character
The tendency of an element to lose electrons and form positive ions or cations
Trend in metallic character across the p-block
Metallic character decreases
Trend in metallic character down the p-block
Metallic character increases
What’s related to metallic character and how?
Electronegativity
As electronegativity increases, the metallic character decreases and vice versa
Where does amphoteric character occur mainly?
In the middle of the period table, here the elements Be, Zn, Al, Ga, In, Sn and Pb are found
Elements in group 2 which show amphoteric behaviour
Beryllium
Elements in group 3 which show amphoteric behaviour
Aluminium, gallium, indium
Elements in group 4 which show amphoteric behaviour
Tin, lead
Transition elements which show amphoteric behaviour
Zinc
Amphoteric behaviour
The oxide and hydroxide will react with acids and bases to form salts
What are oxides and hydroxides of group 1 and 2?
Basic
What does the fact that the oxides and hydroxides of group 1 and 2 are basic mean?
They only react as acids
How does an element behave if it’s demonstrating amphoteric behaviour?
As either an acid or a base
If something reacts with an acid, how does it behave?
As a base
If something reacts with a base, how does it behave?
As an acid
Describe the electronegativity values of elements that show amphoteric character
Intermediate
Describe the bonding of elements that show amphoteric character
It’s changing in character from ionic to covalent
Describe whether the elements that show amphoteric character are metals or non-metals
On the region of the periodic table where the elements are changing from being metals to non-metals
What are all of the elements which show amphoteric characters?
Metals with relatively high electronegativity
What type of bonding do elements that demonstrate amphoteric character have?
Ionic or covalent bonding
How does a hydroxide form in the amphoteric character equations?
By the addition of sodium hydroxide solution to a salt solution of the metal
Aluminium hydroxide showing basic behaviour equation
Al(OH)3 + 3H+ —> Al3+ + 3H2O
Aluminium hydroxide showing acidic behaviour equation
Al(OH)3 + OH- —> [Al(OH)4]-
Tetrahydroxe aluminate (III)
[Al(OH)4]-
Lead hydroxide showing basic behaviour equation
Pb(OH)2 + 2H+ —> Pb2+ + 2H2O
Lead hydroxide showing acidic behaviour equation
Pb(OH)2 + 2OH- +H2O —> [Pb(OH)4]2-
Tetrahydroxo plumbate (II)
[Pb(OH)4]2-
What happens if lead (II) hydroxide is reacted with nitric acid?
An aqueous solution of lead (II) nitrate is formed
What happens when lead (II) hydroxide is reacted with sodium hydroxide?
An aqueous solution of sodium plumbate is formed
What do we need in an question if we have a metal oxide and a base?
Water to balance it out
Equation for lead oxide showing basic behaviour
PbO + 2H+ —> Pb2+ + 2H2O
Equation for lead oxide showing acidic behaviour
PbO + 2OH- + H2O —> [Pb(OH)4]2-
Which elements react with sodium hydroxide solution violently to form a salt and release hydrogen gas?
Aluminium, zinc and beryllium
What do alumnimum, zinc and beryllium do when reacting with sodium hydroxide?
React violently to form a salt and release hydrogen gas
What is it that usually reacts with NaOH to release hydrogen gas?
Acids
What is an additional characteristic property of amphoteric behaviour?
Aluminium, zinc and beryllium reacting with sodium hydroxide solution violently to form a salt and release hydrogen gas
Equation for the reaction between aluminium and hydroxide
2Al + 2OH- + 6H2O —> 2[Al(OH)4]- + 3H2
Which elements does the violent reaction with sodium hydroxide NOT occur with?
Tin and lead
What is the only amphoteric group II element?
Beryllium
What is the only thing really that beryllium has in common with the other group II elements?
It has 2 electrons in the s-orbital
How is beryllium different to the other group 2 elements?
It’s oxide and hydroxide are amphoteric
How are many of beryllium’s compounds?
Covalent
Example of a covalent compound contains beryllium
BeCl2
Why are many of beryllium’s’ compounds covalent?
A consequence of its small size and comparatively large electronegativity which favours the formation of covalent bonds
Why does beryllium favour the formation of covalent bonds?
Small size and comparatively large electronegativity
What are the properties of beryllium closer to than the properties of other group II elements?
Closer to those of aluminium
Alkali
A soluble base
Silicon oxide (IV)
SiO2
Phosphorus pentoxide
P2O5
Describe the elements on the right hand side of the periodic table
Acidic
How can we investigate amphoteric behaviour in a practical?
By adding aqueous sodium hydroxide solutions to a number of aqueous salt solutions
Method for investigating amphoteric behaviour by adding aqueous sodium hydroxide solutions to a number of aqueous salt solutions
1.) place 4cm^3 of the zinc sulfate solution in a test tube
2.) to this solution, add sodium hydroxide solution drop wise until a precipitate forms
3.) divide the precipitate into 2 equal amounts
4.) to the first portion, add nitric acid slowly until it is in excess
5.) to the second portion, add sodium hydroxide solution slowly until it is in excess
6.) note all observations
7.) repeat the experiment with lead (II) nitrate and aluminium chloride
What do zinc, lead and aluminium all have in common?
All show amphoteric behaviours
What was the observation for adding the initial sodium hydroxide to zinc sulfate, lead (II) nitrate and aluminium chloride?
White precipitate
Why do we add the initial sodium hydroxide in the investigating amphoteric behaviour experiment?
To get the elements which show amphoteric behaviour (zinc, lead (II) and aluminium) to be as hydroxides
What’s the observation when adding both excess nitric acid and excess sodium hydroxide to the zinc, lead (II) and aluminium hydroxides?
Precipitate dissolves
Colourless solution
What word do we always use to describe a “clear” solution?
Colourless
What’s happened to a precipitate when it’s no longer visible?
Dissolved
Why do we add both excess nitric acid and excess sodium hydroxide in the investigating amphoteric behaviour experiment?
To see the hydroxides of zinc, lead (II) and aluminium react in the same way with both acids and bases = amphoteric behaviour
equation for the reaction between lead (II) ions and hydroxide ions
Pb ^2+ (aq) + 2OH- (aq) –> Pb(OH)2 (s)
equation for the reaction between lead (II) hydroxide and sodium hydroxide solution
Pb(OH)2 + 2OH- –> [Pb(OH)4]^2- (aq)
(sodium is a spectator ion)
equation for the reaction between aluminium ions and hydroxide ions
Al^3+ (aq) + 3OH- (aq) –> Al(OH)3 (s)
equation for the reaction between aluminium hydroxide and sodium hydroxide solution
Al(OH)3 + OH- (aq) –> [Al(OH)4]- (aq)
how do we identify complex ions?
placed in square brackets
what type of ion is one in square brackets?
a complex one
[Pb(OH)4]2-
tetrahydroxo plumbate (II)
[Al(OH)4]-
tetrahydroxo aluminate (III)
what do the roman numerals represent in the complex ions equations?
the oxidation state of the lead/aluminium
tetrahydroxo plumbate (II)
[Pb(OH)4]2-
tetrahydroxo aluminate (III)
[Al(OH)4]-
latinised name of lead
plumbum
latinised name of aluminium
alum
how do we explain why metals form amphoteric oxides and hydroxides?
their electronegativity values are intermediate (lie between a metal and a non-metal
what happens to an aluminium metal when exposed to oxygen?
forms an oxide spontaneously
why would there be no initial reaction when trying to react an aluminium metal with something?
aluminium forms an oxide spontaneously when exposed to oxygen –> need to get through the oxide layer first
what are the group II elements we will study the most?
boron and aluminium
boron electronic configuration
1s^22s^22p^1
aluminium electronic configuration
[Ne]3s^23p^1
what do both boron and aluminium have in common?
both have 3 electrons in their outer shell
oxidation state of boron and aluminium in their compounds
+3
general formula of group III halides
MX3
(x is the halide)
structure of boron (III) chloride or boron fluoride
trigonal planar
number of electrons around boron and aluminium
6
what can we see about boron and aluminium due to the fact that they have 6 electrons around them?
they’re short of an octet = electron deficient
what does it mean if something is short of an octet?
is electron deficient
can boron and aluminium gain a pair of electrons readily?
yes
how come boron and aluminium can gan a pair of electrons readily?
they have strong electron acceptor properties
what are the electron acceptor properties of aluminium chloride reflected in?
the ready formation of the dimer Al2Cl6
what is Al2Cl6?
a dimer
what is the dimer Al2Cl6 made up of?
2 aluminium chloride molecules have combined
what type of bonds form to form an Al2Cl6 dimer?
co-ordinate bonds
how are co-ordinate bonds formed in the Al2Cl6 dimer?
by each aluminium atom accepting a lone pair of electrons from one of the chlorine atoms in the other molecule
why is the Al2Cl6 dimer able to form?
aluminium has a vacant 3d orbital
chlorine has a lone pair of electrons
is aL2cL6 electron deficient?
no
bonding in AlCl3
covalent
bonding in AlF3
ionic
bonding in Al2O3
ionic
properties of AlCl3 with its covalent bonding
sublimes at 180 degrees celcius (fairly low temperature)
decomposes in water
exists as dimers, Al2Cl6, when solid and as monomers
AlCl3 in the gaseous state
state of AlCl3
gaseous
when does AlCl3 exist as Al2Cl6??
when solid and as monomers
properties of AlF3 with its ionic bonding
melts at around 1300 degrees celcius
dissolves readily in water
molten alumnium fluoride is a good conductor of electricity
properties of Al2O3 with its ionic bonding
melts at 2100 degrees celcius
insoluble in water
conducts electricity when molten
which bonding is exhibited between aluminium and oxygen and fluorine and why?
ionic
large electronegativity
with which elements does aluminium exhibit ionic bonding and why?
with oxygen and fluorine
large electronegativity
what type of bonding does a large electronegativity usually lead to?
ionic
which type of bonding happens with less electronegative elements?
covalent
apart from with oxygen and fluorine, when else does aluminium exhibit ionic bonding?
when hydrated with water
why does ionic bonding occur in aluminium when hydrated with water?
large hydration energy owing to the very small size of the aluminium ion
list some aluminium elements that exhibit ionic bonding
AlF3
Al2O3
[Al(H2O)6]^3+
list some aluminium elements that exhibit covalent bonding
Al2Cl6
AlBr3
Al2H6
give an example of a donor-acceptor compound
ammonia-boron trifluoride
ammonia-boron trifluoride equation
NH3BF3
when is ammonia-boron trifluoride formed?
when ammonia reacts with boron trifloride, forming a co-ordinate bond
how are donor-acceptor compounds formed?
when one atom, having a lone pair of electrons to donate, reacts with another atom, which is electron deficient (i.e - has an empty orbital to accept the electron)
what type of bonding is in a donor-acceptor compound?
coordinate
what does each central atom have around it in a donor-acceptor compound?
an octet
why is ammonia-boron trifloride able to form?
nitrogen in ammonia: has a lone pair of electrons which is available for bonding
boron in boron trifluroride: has only 6 electrons in its outer shell
therefore, boron attains a full shell of electrons in forming a co-ordinate bond with the lone pair of electrons from the nitrogen
which group element is nitrogen?
group V
describe boron
electron deficient group III element
how many electrons does aluminium have in its outer shell in aluminium chloride and what does this mean?
6
is electron deficient
what happens when aluminium chloride reacts with a chloride ion?
aluminium will readily accept a lone pair of electrons from a chloride ion to form the complex ion tetrachloroaluminate (III)
[AlCl4]-
tetrachloroaluminate (III)
tetrachloroaluminate (III) ion
[AlCl4]-
equation for the reaction between aluminium chloride and chloride ions
AlCl3 + Cl- ⇌ AlCl4-
why will aluminium readily accept a lone pair of electrons from a chloride ion to form the complex ion tetrachloroaluminate (III)?
since aluminium in aluminium chloride only has 6 electrons in its outer shell (is electron deficient)
What leads to aluminium chloride being an industrially important catalyst?
the affinity of AlCl3 for chlorine species
what does the affinity of aluminium chloride for chlorine species lead to?
it’s an industrially important catalyst
examples of industrially important catalysts that aluminium chloride forms
AlCl3 - catalysed Friedel-crafts reactions. there is no need to heat when carrying out reactions = saves energy
Low melting temperature ionic liquids, which contain the chloroaluminate (III) ion, [AlCl4]- are being developed as “clean technology” catalysts for the polymerisation of alkenes. the ionic liquid contains the chloroaluminate (III)) ion and a large organic cation.
why is boron nitride of interest to us?
as the B-N bond is similar to the C-C bond
which 2 words can be used to describe boron nitride and its comparisons to carbon?
isoelectronic (with the elemental forms of carbon)
isomorphism (occurs between the 2 species)
isoelectronic
the same number of electrons or the same electronic structure
isomorphism
similar chemical composition and exist in the same crystalline form
the same number of electrons or the same electronic structure
isoelectronic
similar chemical composition and exist in the same crystalline form
isomorphism
how many electrons do both C-C and B-N bonds have between the 2 atoms?
12
describe the structure of boron nitride
giant covalent
what are the giant covalent structures of boron nitride?
hexagonal
cubic
what is hexagonal boron nitride isomorphic with?
graphite
what is hexagonal boron nitride with graphite?
isomorphic
similarities between hexagonal boron nitride and graphite
high melting and boiling points
softness
insoluble
why do both hexagonal boron nitride and graphite have high melting and boiling points?
each atom forms 3 or 4 covalent bonds which require a lot of heat energy to overcome
why are both hexagonal boron nitride and graphite soft?
weak van der waal forces allow them to slide over each other
what does the feature that both graphite and hexagonal boron nitride are soft allow them to be used as?
a lubricant
how come hexagonal boron nitride and graphite can be used as a lubricant? explain this
they’re both soft
weak van der waal forces allow them to slide over each other
why are both hexagonal boron nitride and graphite insoluble?
no charges particles to react with the permanent dipole of water molecules
differences between hexagonal boron nitride and graphite
hexagonal boron nitride is an electrical insulator, whereas graphite is an electrical conductor
atoms in adjacent layers in hexagonal boron nitride are in register. in graphite, they’re out of register
electronegativity difference between boron and nitrogen = polar B-N bonds. no electronegativity difference between the carbon atoms in graphite (all atoms are the same).
how come the bonds between B and N in boron nitride are polar?
electronegativity difference
how come hexagonal boron nitride is an electrical insulator whilst graphite is an electrical conductor even though they’re isomorphic?
hexagonal boron nitride only has localised electrons due to the large electronegativity difference between the nitrogen and boron atoms = no free electrons
in graphite, electrons are evenly delocalised (non-bonding electrons)
uses of hexagonal boron nitride
used in electronics as a substrate for semi-conductors
ceramics
microwave windows
catalyst carrier in fuel cells and batteries
single layers can be wrapped to create nanotubes
how are nanotubes created?
single layers of hexagonal boron nitride are wrapped
which property of hexagonal boron nitride allow them to be used in electronics as a substrate for semi-conductors?
electrical insulator
what can hexagonal boron nitride be used for due to it being an electrical insulator?
can be used in electronic as a substrate for semi-conductors
what is cubic boron nitride isomorphic with?
diamond
what is cubic boron nitride with diamond?
isomorphic
similarities between cubic boron nitride and diamond
hard
strong
extremely high melting and boiling points
insoluble
electrical insulator
Tetrahedral arrangement of atoms
why are both cubic boron nitride and diamond hard?
each atom is bonded to 4 others with a strong covalent bond = structure held together in a rigid 3D structure
why do both cubic boron nitride and diamond have extremely high melting and boiling points?
each atom has 3 or 4 covalent bonds which require a lot of heat energy to overcome
why are both cubic boron nitride and diamond electrical insulators?
no delocalised electrons in the structure to carry voltage
differences between cubic boron nitride and diamond
cubic boron nitride isn’t as hard as diamond = preferred for grinding certian materials
cubic boron nitride is more stable due to the lack of electronegativity difference between the atoms
diamond can react with transition metals like iron and above 800 degrees celcius can react with air to form CO2
Cubic boron nitride is a good thermal conductor