Describe what happens (give chemical equations only) when:
(i) carbon monoxide is treated with chlorine.
(ii) carbon monoxide is passed through heated NaOH under pressure.
(iii) Vapours of carbon monoxide are passed over nickel and
(iv) carbon monoxide is passed through heated ferric oxide.
Aluminium trifluoride is insoluble in anhydrous HF but dissolves on the addition of NaF. Aluminium trifluoride precipitates out of the resulting solution when gaseous BF3 is bubbled through. Give reasons.
(i) Anhydrous HF, being a covalent compound and is strongly H-bonded, therefore it does not give ions. Hence AlF3 does not dissolve in HF. On the other hand, NaF is an ionic compound and gives F– ions and hence AlF3 dissolves in NaF forming soluble complex
(ii) Borax has much higher tendency to form complexes than aluminium because of its smaller size and higher electronegativity. Hence when gaseous BF3 is bubbled through the resulting solution. AlF3 gets precipitated.
Suggest a reason why the B - F bond lengths in BF3 (130 pm) and (143 pm) differ?
Why B - F bond length in BF3 is smaller than the expected value?
In BF3, boron is sp2 hybridised and therefore BF3 is a planar molecule. It has a vacant 2p-orbital. F-atom has three lone pairs of electrons. In BF3 molecule, one 2p-orbital of fluorine atom overlaps sidewise with empty 2p-orbtial of boron to form back bonding (back donation) in which the lone pair is transferred from F to B as shown.
As a result of this back bonding (or black donation), the B-F bond acquires some double bond character.
On the other hand in ion, boron is sp3 hybridised and therefore is a tetrahedral molecule. B in ion does not have vacant p-orbital available to accept the electrons donated by the F atom. Hence ion, B -F is a purely single bond. Since double bonds are shorter than single bonds, therefore B-F bond length in BF3 is shorter (130 pm) than B-F bond length (143 pm) in [BF4]–.
Discuss the pattern of variation in the oxidation states of B(Boron) to Tl(Thallium).
What is inert pair effect? Illustrate it with reference to Boron family.
Inert pair effect:The inert pair effect represents the reluctance of the valence electrons to take part in the chemical combination due to their penetration in the nucleus of heavy elements.
B and Al do not exhibit inert pair effect due to the absence of d – or f-electrons. As a result, they show an oxidation state of +3 only due to the presence of two electrons in the s– and one electron in the p-orbital of the valence shell.
On the other hand, the elements from Ga to Tl contain only d and f-electrons and hence show oxidation states of +1 and +3 due to inert pair effect.
As we move down the group, the stability of +3 oxidation state decreases and that of +1 oxidation state increases. This means that as we move down the group, the tendency of the electrons of the valence shell to participate in bond formation decreases. In other words, ns2 electron pair in Ga, In and Tl tends to remain paired. This is called inert pair effect. Because of inert pair effect, only the electron of thallium takes parts in bonding with the atoms of the other elements. Thus, monovalent compounds of thallium are stable.
Explain structures of diborane. Write the structures of diborane and explain the nature of bonding in it ?