Class 12th

In [Ni (Cl)₄]^2- ion, Cl^- is a weak field ligand so it will not pair the unpaired electrons of Ni⁺² ion. Electronic configuration of Ni is: [Ar]3d⁸4s² where [Ar] = 1s²2s²2p⁶3s²3p⁶

Electronic configuration of Ni⁺² = [Ar]3d⁸ Outer electronic configuration of Ni⁺² = 3d⁸ Overall charge balance:

X + 4 (-1) = -2 X = + 2.

Therefore it undergoes sp³ hybridization. So it will have tetrahedral geometry.

Since there are 2 unpaired electrons in the d orbital so it is a paramagnetic compound. In [Ni (Co)₄]:

Overall charge is neutral and oxidation state of Ni can be calculated as:

X + 4 (0) = 0

x = 0

Ni is in zero oxidation state.

Co is a strong field ligand it causes pairing of the 4 unpaired electrons in d orbital. Also, it causes the 4s electrons to shift to the 3d orbital, thereby undergoes sp³ hybridisation forming tetrahedral geometry. Since it has no unpaired electron, therefore it is diamagnetic compound.

According to the valence band theory, the central metal atom or ion under the influence of ligands can use its (n-1)d, ns, np (inner orbital complex) or ns, np, and (outer orbital complex)orbitals for hybridisation to form equivalent set of orbitals of definite geometry.

In [Ni (CN)₄]^2-, oxidation state of Ni can be calculated as :

Using overall charge balance as the whole ion has overall -2 charge:

x + 4 (-1) = -2 (? CN^- has -1 negative charge) x = + 2

Ni is in + 2 oxidation state.

Electronic configuration of Ni is: [Ar]3d⁸4s² Where, [Ar] = 1s²2s²2p⁶3s²3p⁶

Electronic configuration of Ni⁺² = [Ar]3d⁸ Outer electronic configuration of Ni⁺² = 3d⁸

Since there are 4 CN ions so they can either form tetrahedral or square planar geometry. And CN^- is a strong field ligand (according to experimental data of spectro-chemical series) it causes pairing of the 2 unpaired electrons.

It undergoes dsp² (one d orbital, one s and two p orbitals used by the ligands) hybridization and forms square planar structure.

Since all the electrons are paired so it is diamagnetic.

Paramagnetic compounds- those compounds which have one or more no. of unpaired electrons in their atomic orbitals.

Diamagnetic compounds-those compounds in which all the electrons in their atomic orbitals are paired.

In case of [Ni (Cl)₄]^2- ion, Cl^- is a weak field ligand so it will not pair the unpaired electrons of Ni⁺² ion. Therefore it undergoes sp³ hybridization.

Overall charge balance: X + 4 (-1) = -2

X = + 2.

Since there are 2 unpaired electrons in the d orbital so it is a paramagnetic compound.

14.25

Enzymes are naturally occurring simple conjugate proteins acting as specific catalysts in all processes. In contrast to ordinary chemical catalyst, it loses activity by pH or temperature change.

For example:- the enzyme used to catalyze the hydrolysis of maltose into glucose is named as maltase.

Enzymes are highly specific, i.e., a particular enzyme catalyses a specific reaction. For example, urase attacks on urea. This specific action is due to active sites present in the enzyme molecule (E) that fits into substrate (S) and forms E-S complex which changes into product P and E.

Enzymes increase the speed of reactions. They can catalyze several million of reactions per second.