T1- p Block LP4

Question 1

What is the name given to group 14?

Answer 1

Tetrels

Question 2

What are the elements in group 14?

Answer 2

Carbon, silicon, germanium, tin and lead

Question 3

What is allotropy?

Answer 3

Is the property of some chemical elements to exist in two or more different forms, with distinct structures.

Question 4

What is the trend of hydrides in group 14?

Answer 4

Stability decreases down group because element-H bonds weaker as group descending - larger, more diffuse orbitals, more polar bonds, motal not shielded and LUMOs low-lying.

Question 5

Why for Ge, Sn, Pb we can form MX₂ compounds and for C and Si we form MX₄?

Answer 5

Because bonds aremore polar, low lying LUMOs and their are electrophilic metals or metalloids.

Question 6

Why silicones have a high thermal and chemical stability?

Answer 6

Because it has very strong Si-O bonds, where an empty silicon 3d orbital overlaps with filled oxygen 2p orbital.

Question 7

Why it is easy to make double and triple bonds with first row elements but not with others?

Answer 7

It is because orbital overlap is good. Orbital overlap to make π bonds with heavier group 14 elements are possible, but σ bonds will always form preferentially if possible.

Question 8

How can we form π bonds with heavier group 14 elements?

Answer 8

By reacting them with bulky, sterically demanding groups. This will block oligomerization. This stops metal centres polymerising via σ bonds and forces them forming π bonds.

Question 9

What is oligomerization?

Answer 9

It is a chemical process that converts monomers to macromolecular complexes through a finite degree of polymerization

Question 10

Why R₄Sn₂ dissociate in solution to 2 R2Sn?

Answer 10

It is because lone pair in Sn goes into empty p orbital. This is weaker than covalent bonding.

Question 11

In general, what Zintl phases contain?

Answer 11

Group 1 or group 2 metal, along with post-transition metals (g12) or the metalloids from groups 13, 14, 15 or 16.

Question 12

If you were trying to produce a siloxane, which would be the most suitable starting material?

Answer 12

The starting point would be to take an organohalide, such as trimethylsilyl chloride, Me3SiCl, and react with water to form the silanol (e.g. Me3SiOH) and HCl. The silanol then goes on to further react by dehydration and produce the siloxane.

Question 13

What are cryptands?

Answer 13

Bicyclic (or polycyclic) multidentate ligands.

Question 14

What are zintyl ions?

Answer 14

An anionic clusters of a single element, which can be formed by reduction using Na metal in liquid ammonia.

Question 15

How group 15 elements are called?

Answer 15

Pnictogens

Question 16

What are group 15 elements?

Answer 16

Nitrogen, phosphorus, arsenic, antimony, bismuth.

Question 17

What is electron configuration of pnictogens?

Answer 17

ns²np³

Question 18

Why hydrides of group 15 are stable exept BiH₃?

Answer 18

Because bond energy decreases down the group, thus stability decreases.

Question 19

Why PH₃ is not basic as NH₃?

Answer 19

P-H bonds are mainly sigma character and 3s orbital contributes little to the bonding the lone pair is predominantly formed by the 3s orbital of phosphorous.

Question 20

How phosphines bond to the metal?

Answer 20

π bonding involves overlap between σ* orbital on P and filled metal d-orbital.

Question 21

Why as you increase the bulk of the R group the angle increases?

Answer 21

Because of the steric interactions between R groups.

Question 22

How ethyl groups affect π back bonding?

Answer 22

The ethyl groups have a positive inductive, +I, electronic effect i.e. they push electron density towards the P atom. This means that the P donor atom of the ligand is more electron-rich and hence less able to accept electron density from the metal via π-back bonding.

Question 23

What is the oxidation state of nitrogen in nitrogen dioxide?

Answer 23

+4, because nitrogen dioxide is a radical, with the central N atom possessing an unpaired electron. Oxygen is the more electronegative element and is generally assigned an oxidation state of -2 in most compounds. If the O atoms were removed as oxide ions (O2-) then the N atoms would be left with a single valence electron (the unpaired electron)

Question 24

Why might reacting certain group 15 elements with hydrogen fluoride be particularly dangerous?

Answer 24

The primary hazard would be the formation of a super acid. In the case of SbF₅ and AsF₅, reaction with HF would form a species that is even more acidic than HF alone

Question 25

What is the evidence for Berry pseudorotation of PF₅?

Answer 25

Berry pseudorotation allows the exchange of axial and equitorial atoms in a trigonal bipyramid. Since this process occurs faster than the timescale of NMR spectroscopy, the measurement cannot distinguish between the two positions and instead “sees” and average. Therefore, the ¹⁹F NMR spectrum does not show separate multiplets for the axial and equitorial F nuclei. Instead it shows a single peak corresponding to all 5 F atoms. This peak is split into a doublet by coupling from the spin-active P.