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