p block (G13-15) Flashcards
what is the trend for metallic character in the p block and how does it relate to ionisation energy?
increase in metallic character means an element has a low ionisation energy
metallic character decreases across and period and increases down a group
why do the size of atoms in G13 and G14 not change as much as you move down the group?
d block contraction: electrons in d orbitals have different screening properties compared to s and p, they screen the outer electrons less, thus the outer electrons experience a greater than expected Zeff
f block contraction: electrons in f orbitals have different screening properties compared to s and p, they screen the outer electrons less, thus the outer electrons experience a greater than expected Zeff
What is the name of the product formed by combining a Lewis acid and base
Lewis acid Lewis base adduct
Why are the properties of period 2 elements slightly different than the periods below
Period 2 elements cannot have an expanded octet as they do not have d orbitals of similar energy (low lying) to fill
How does the oxidation state change down G13 and why?
+3 for top of group and goes down to +1
Inert pair effect:
1. orbitals become more diffuse due to poorer overlap (bond energies decrease)
2. Due to the d and f block contraction promotional energy from s to p (for bonding) required increases
As you go down the group the energy required for promotion is much greater than the energy released by formation of a bond, thus the +1 is favoured over + 3
Why does boron lack metallic character
High ionisation energies due to its reluctance to form a positive charge
Why is aluminium corrosion resistant?
Forms an oxide layer that is impermeable
What is rule of thumb for +3 or +1 oxidation state in G13
2 bond energies > promotional energy then +3
2 bond energies < promotional energy
then + 1
Why are borotrihalide bonds shorter than expected?
The sp2 hybridized boron has an empty p orbital orthogonal to the trigonal plane. The empty orbital is parallel to the lone pairs of the halides thus electron density can be transferred which partially stabilises and shortens the bond
What is the order of Lewis acidity of boron trihalides and why?
BF3 is the least Lewis acidic because it has the best orbital overlap thus most donation into the lone pair (which decreases the availability of the empty orbital to be attacked by a Lewis base)
> thus BI3 is the best Lewis acid due to least electron donation into empty B orbital
What occurs when AlCl3 is vaporised and why?
Forms dimers Al2Cl6 because it’s valence electrons are in a more diffuse orbital thus overlap is poorer, and it cannot rely on electron donation in the same way that boron halides do (to relieve electron deficiency)
What determines the reaction between a boron trihalide and a Lewis base?
HSAB theory
What is the boron dimer and why does it form
BH3 is unstable as the H has no lone pairs to stabilise the empty p orbital so it dimerizes to form B2H6
What is the bonding found in diborane?
3 center 2 electron bonds (MO theory)
dimer
what are the names of the compounds that G14 elements form and what is the oxidation state of those compounds?
+ 4: dioxides
-4: hydrides
how does the oxidation state change going down G14?
+4 to +2 due to the inert pair effect
how does metallic character change down G14?
metallic character increases from non metal to metaloides to metals
what are the 5 main allotropes of carbon?
diamond: sp3 (hard, electrical insulator but thermal conductivity is good)
graphite: sp2 (electrical conductor parallel to layers, staggered layers, weak attraction between layers makes good lubricant, 3 sigma 1 pi that can be delocalised, can intercalate -> put positive ion between)
fullerenes
graphene
carbon nanotubes
Describe the conductivity of graphite
Only conductive within the layer due to the overlap of pi orbitals overlapping within the layer. The pi bonded electron can travel within the layer but NOT to other layers
Describe the structure of graphite
Strong intralayer bonding (covalent) weak interlayer bonding (VdW)
What are intercalation compounds with graphite
Insertion of something in between the layers of graphite
What is metability for diamond?
Metastability is being stable for a certain period of time, this is true for diamond as after long periods of time it turns into graphite. But transition is very slow due to the small thermodynamic change.
What are the properties and structure of fullerenes?
- Alternating pentagonal and hexagonal rings
- alternating double and single CC bonds
- localised C=C can undergo addition reactions
- all carbons are in the same environment (1 C13 NMR peak shown)
What structures do Ge and Si form and why?
Diamond like structures as their p-p overlap is much weaker thus would not unfavourably be sp2 and it prefers forming 4 strong covalent bonds rather than 3
What are the 2 polymorphs (2 different crystal structures) of tin and their properties?
6 coordinate: white tin at 298K
4 coordinate: grey tin at 286K (diamond like) -> brittle and unstable
What was lead used for and why is it being phased out?
Plumbing and paints but fading out due to toxicity
Why does carbon have different bonding properties to other elements in the same group?
C does not have low lying d orbitals that it can use to expand its octet while others do
What is the reactivity trend down G14 and why?
Reactivity increases due to the increase in electro positive character
What is catenation?
The ability of an element to form a bond with itself as part of a molecule
Why is carbon much better at catenation than other elements in G14?
Much better orbital overlap thus more energetically favourable and stable
Why do are carbon oxides a gas but silicon oxides a solid?
C and O are on the same period -> good orbital overlap -> can form multiple bonds which are content
Si and O have much weaker orbital overlap (3p and 2p) so it cannot form
multiple bonds and thus forms single bonds instead resulting in a macromolecular structure (strong covalent network)
How does the Lewis acidity change with its substituents?
Lewis acidity increases with more electronegative substituents as it draws electron density away from the central element making it more available to accept electron pair
Why do G14 elements except for carbon readily hydrolyse
Low lying d orbitals that can accommodate extra electrons
How does metallic character change down group 15?
Non metal -> metalloid -> metal
Explain the differences between NN single bond and NN triple bond
N triple is very inert due to lack of dipole moment and high dissociation energy (good orbital overlap)
N single bond is much weaker due to the LPLP repulsion on both nitrogen’s (also bc they are small and close together so extra repulsion)
What are the 3 allotropes of phosphorous and what are their properties?
White P4 phosphorous: strained structure (tetrahedron) that is highly reactive (ignites in air) and can act as a Lewis base
Black phosphorous: 6 membered rings, thermodynamically stable (least reactive form)
Red phosphorus: between black and white reactivity (chain of tetrahedral linked through a broken bond of p4)
How does a match work
Red phos vaporises due to friction-> white phos -> ignites which makes KClO3 to form O2 which feeds oxygen to the sulphur on the match head which causes the fire
How is P4 stabilised? 2 ways
- Reaction with sulfuric acid to form phosphoric acid
- Reaction with chlorine gas to form PCl3
What must happen to nitrogen in its +5 oxidation state
Form multiple bonds as it cannot accommodate 5 different substituents (too small)
What is the Lewis acidity/basicity of G15 elements?
Lewis base and acid for EX3 as it has a lone pair and low lying d orbitals (except for nitrogen)
What affects Lewis acidicty/basicity of G15 EX3 elements and why?
The higher the electronegativity of the X group, the more acidic it is as the electronegativity makes the lone pair less available
What is the Lewis basicity/acidity of EX5 molecules in G15 and why?
Only Lewis acid bc of low lying d orbitals but no lone pair
What evidence exists for ionic character in PCl5?
Existence of PCl6- and PCl4 + (transfer of charges)
Why can P from G15 form oxides?
Strong ionic component and P can accept electrons into low lying d orbitals
What are phosphines?
Compounds with a P-C or P-H bond
how is boric acid formed ?
- hydrolysis (addition of water) of borotrihalides (except for flourine)
- from elemental boron add oxygen to form boric oxide (B2O3) then add water to form boric acid
what is the colour difference between the elemental and crystalline form of boron?
elemental boron is brown powder while crystalline boron are solid dark crystals (proof of multiple elemental forms)
how is boron produced?
- from BORAX (mineral) which reacts with H2SO4 to form boron hydroxide which is thermally decomposed into boron oxide with acid and basic washes to form elemental boron (harsh conditions required thus not preferred)
- vapour phase reduction eith BBr3 with H2
- pyrolysis of B2H6 or BI3 (heating with insufficient oxygen)
how is aluminium produced?
extracted through electrolysis with bauxite
what are uses of G13 elements?
boron: glass industry (borosilicate -> kitchen and chemical glassware)
aluminium: aircraft and construction due to high strength and low density
the rest are used in semiconductor industry and for LED lights
how can you produce born trihalides?
- halogenation of boron oxides (forms carbon monoxide)
- hydride with halogen (produces hydrogen)
why are B-X bond lengths shorter than expected?
donation of electron density from halide to empty p orbital of boron creates a more stable species (partial double bond character resonancy thing)
how is diborane produced?
reduction of borontrihalide with hydride source
how can higher boranes be produced?
pyrolysis with heat under controlled conditions because the boron hydrogen bonds are broken and can be reformed to form higher order borane compounds
what are uses of some of the G14 elements?
carbon: blackened carbon can be used to reinforce vulcanized rubber
silicon: silica (glass and sand)
tin: coating other metals to prevent its corrosion
how are heavier G14 H compounds formed? which ones are not formed?
By reacting G14 halides and oxides with reducing agents (LiAlH4 and NaBH4)
lead because they decompose too quickly to be useful
which tetrahalide cannot be formed and why? For G14
pb-I bond stabilisation is not enough to compensate for the promotional energy required
pb-cl4 decomposes into pbcl2 and cl2 due to the inert pair effect
what is the lewis acidity or basicity of G14 elements?
all lewis acid except for carbon as they have low lying d orbitals which can accept the electron density (carbon does not)
what can lewis acids of G14 elements react with and why?
can react with water to form EO2 due to low lying d orbitals (not possible with carbon only)
what is the appearance of elements other than nitrogen in G15?
grey solids under standard conditions
combine readily with oxygen to form M2O3 where M is the G15 element
how is black phosphorous formed?
through heating white phosphorous under pressure
how is nitrogen formed? what is its use?
fractional distillation of liquid air
used to provide an inert space for packaging
used in the production of ammonia (used in fertilisers via the haber-bosch process)
how is phosphorous formed? what are its uses?
- extracted from phosphorous rock (to form P4)
- then reacted with sulfuric acid to form phosphoric acid
-> detergents, fertilisers - reacted with chloride to form PCl3
-> insecticides
can RE5 compounds in G15 be lewis bases?
no because there are no lone pairs to donate electron density
what does PX5 exist as in gas/solid/liquid state and what does that prove?
in gas/liquid: PCl5
in solid state: PCl4+ and PCl6-
PCl5 is on the borderline of ionic and covalent bonding
what are the types of oxides phosphorous forms?
phosphate (P with O and OH)
phosphorous (P with 4Os)
phosphine (P with carbon bond)
all have P=O in it
