Core 3: Main Group Flashcards
What are the 3 Fajans rules of polarisability?
- Small, highly charged cations have polarising ability
- Large, highly charged anions are easily polarised
- Cations that dont have a noble-gas electron configuration are easily polarised
Why does phosphorus form P4 shapes in preference to P≡P such as in N2?
Due to the strength of the triple bonds, P4 is more favourable than P2. In N2 there is very strong pi overlap of orbitals but lone pair repulsions weaken the single bond.
What solid state structure will Cs form with 18-crown-6?
Cs+ with an e- counter ion
What is the structures of borazine rings and cyclophosphazenes? Name a reaction which shows the reactivity of borazines compared to benzene.
A 6-membered ring of B(H)-N(H)=B(H)-N(H) and P(Cl2)=N-P(Cl2)=N.
Borazines will react with water to remove all double bonds.
What molecular structure will LiBun resemble in the presence of TMEDA (bidentante ligand)?
Borane structrue with TMEDA ligands as the terminal positions and 2 lithium atoms sharing 2 Bun molecules.
Describe the structure of 18-crown-6, specifically the heteroatoms.
A crown ring of 2 carbon atoms then an oxygen atoms, there is 18 atoms in the ring, 6 of which are oxygen. The oxygen atoms are slightly offset above and below the plane of the crown.
Define isoelectronic.
Where two fragments have the same number of electrons or the same electron configuration.
What happens when sodium is placed in liquid EtNH2 with crypt-2,2,2-and?
A complex forms where Na+ is surrounded by the cryptand and Na- exists in solution.
What are the 4 oxidation states for group 15? Where are they common?
-III, 0, +III, +V
+III is common in all elements, +V is common in the middle
What is the reaction between EX4 and an excess of water where E is a group 14 element? Any exceptions?
EO2 will vigourously form except for carbon which is less likely to form the 5-coordinate intermediate which is required for it to form.
What is the term for an atom that has more than 8 valence electrons?
Hypervalent.
What is the stength of the polarising effect of lithium?
Very polarising as its size is very small so it distorts electron clouds that are much bigger than itself e.g Cl-.
How can cyclophosphazenes bonding be rationalised?
Using the sp2 and s orbitals of N and the d orbitals of P overlap can be shown.
What are the possible fluorides of sulfur? Describe some differences in their reactivity.
S2F2, SF2, SF4 and SF6 are possible. SF4 is highly reactive and toxic, SF6 is extremely inert, non-toxic and used as electrical insulating gas.
How do graphene sheets line up with one another in graphite? Is this the same for hexagonal boron nitride?
The carbon atoms in graphite line up with a gap above it. Hexagonal boron nitride is different and stacks with a boron atom directly underneath a nitrogen atom.
Why does PX5 have a structure where all positions are equal?
The shape undergoes ‘Berry pseudorotation’ sp all postions are equivalent.
Why does Zeff increase across the period?
Electrons in the same type of orbital do not shield each other well.
What nitrogen hailides can form? How do these compare to phosphorus halides? Are these lewis basic or acidic?
N2F2, N2F4, NF3 (other NX3 compounds are contact explosives due to weaker N-X bonds), [NH4]+ and ONH3.
All these halides are possible as well as stable PX3 and PX5. All states except +V are lewis basic.
Which noble gases are possible to form compounds with and what are some examples?
The elements later in the group where ionisation energies are lower can form compounds with strong oxidising elements.
XeF2, XeF4, XeF6 and XeOF4 have all been formed as well as KrF2 and HArF however these are unstable.
What happens when alkali metals are placed in liquid ammonia? What explains this observation?
A conducting, paramagnetic, bright blue solution is formed as an electron is released from the metal which is then solvated and has a virtual 1s→2p transition resulting in the blue colour.
How will RMgX react with LiR and HgR2? Describe its bonding
It will form MgR2. A 3c2e structure similar to borane forms.
Which halides, and with which elements, will oxidation states other than -I be formed?
All but F will form the hailides and will form with O or F.
What is the trend for oxidation states of the group 13 elements?
At the top +III is most common but the inert pair effect means that +I becomes common down the group
Name 3 similarities between Li and Mg, elements with a diagonal relationship
- Both will form nitrides, Li3N and Mg3N2 unlike other group 1 elements.
- Their carbonates will decompose to CO2 at much lower temperatures.
- Both will form covalent organometallic compounts.
