T2- s Block LP3 + LP4

Question 1

What H₂O ligands form with alkali metals?

Answer 1

With Li it forms 4 ligands as it is smaller and with other metals 6 ligands.

Question 2

What are crown ethers?

Answer 2

Are cyclic chemical compounds that consist of a ring containing several ether groups also called macrocytcles. Macrocycles and related ligands form very stable complexes with alkali metals.

Question 3

What is macrocyclic effect?

Answer 3

It is a combination of an entropic effect as seen in the chelate effect, together with an additional energetic contribution from the preorganised nature of the ligands.

Question 4

What are cryptands?

Answer 4

A coordination complex in which a metal cation is bound within a cavity in the molecule of a cryptand

Question 5

Why in contrast to crown ethers the cryptants show peak selectivity?

Answer 5

It is because macrobicydic cavities of cryptands are more rigit- cannot constrict sufficiently to bind cations which are too small for the cavity and cannot expand ro accomodate cations with radii signifacantly larger than the optimum size fit. Crown ethers can change the size of their cavities.

Question 6

What is alkalide?

Answer 6

It is a chemical compound in which an alkali metal is in an anion and it is in the -1 state.

Question 7

What are electrides?

Answer 7

Compounds with solvated electrons:

Na +6NH₃ —-> [Na(NH₃)₆]⁺e^-

Question 8

What pyrophoric means?

Answer 8

Material that can spontaneously ignite in air.

Question 9

Why ionic character of the M-C bond increases down the group?

Answer 9

Because metals become larger and less polarising.

Question 10

When number of alkyl groups in organometallic compound increases how basicity changes?

Answer 10

Basicity increases and eactivity increases

Question 11

Why organolithium compounds (LiR) aggregate?

Answer 11

Due to electron deficiency forming [LiR]_n by the formation of multicentre bonds e.g. for [LiMe]₄

Question 12

Where are Li located in organlitium compound with 4 Li sp³- hybrids per Li atom?

Answer 12

1x axial, identical with the tetrahedron threefold axes

3x tangential, pointing out of the triangular faces

Question 13

When the organic anion is particularly stable the interaction of the metal cation with the carbocation may be much weaker then with the solvent, why is that?

Answer 13

Because metal form interactions with the solvent than carbocation.

Question 14

How is this compound called?

Answer 14

Naphthalenide dianion salt

Question 15

Why are group 1 elements strong reducing agents?

Answer 15

The Group 1 elements have a loosely bound valence electron and low electronegativities, therefore lose their electron easily.

Question 16

Why are the Group 1 elements poor complexing agents?

Answer 16

The alkali elements have a low positive charge and relatively large ionic radii, so they only possess a weak tendency to form complexes with simple Lewis bases. Li+ is the most effective at forming complexes, and this tendency decreases with increasing radius (down the group).

Question 17

Is Li⁺ or K⁺ more likely to form a complex with 2.2.2-crypt? Discuss the physical basis for your answer

Answer 17

K+ is more likely to form a complex with 2.2.2-crypt as this ligand shows peak selectivity for K⁺ . Cryptands cannot constrict sufficiently to bind cations which are too small for the cavity and cannot expand to accommodate cations with radii significantly larger than the optimum size fit

Question 18

How can the following equilibrium be pushed to the RHS?

2Na <====>Na⁺+ Na^-

Answer 18

Addition of a cryptand complex the Na⁺ and push the equilibrium to the RHS

Question 19

Why do LiF and CsI have low solubility in water whereas LiI and CsF are very soluble?

Answer 19

In general, for salts containing the large anions, in general the solubility decreases down the group (and therefore Li+ salts would be the more soluble). For salts containing the smaller anions, the solubility increases down the group (and therefore the Rb+ and Cs+ salts would be the most soluble). Due to differences between lattice enthalpy and hydration enthalpy. In more detail: the low solubility of LiF can be attributed to the high lattice enthalpy of this salt, which is not offset by the hydration enthalpy. In comparison, for LiI the size of iodide ion is much greater than fluoride ion, and therefore its lattice energy comparatively lower than LiF, and, as a result, LiI is more soluble in water. For CsI, both ions are large in size, and, as a result the hydration enthalpy is small and cannot offset the lattice enthalpy, and for CsF, this hydration enthalpy is higher than the lattice enthalpy leading to greater solubility in water.