What is lanthanoid contraction?

The overall decreasing in atomic and ionic radii from lanthanum to leutetium due to imperfect shielding of 4f e- from nuclear charge. this is called lanthanoid contraction. the steady decrease in size of lanthanoid with the increasing atomic number is known as lanthanoid contraction.

The basic concepts of lanthanoid contraction is, there are regular decrease of atomic size from lanthanoid to leutetium. this is due to imperfect shielding of 4fe- from nuclear charge. as shown in figure. According to the structure, the overall decreasing in atomic and redii from lanthanoid to leutetium is observed in the lanthanoids. it is due to every additional proton in the nucleus, the corresponding electron goes into a 4f-subshell.

It is too diffused to screen the nucleus as effectively as the more localised inner shell. due to this reason, the attraction of the nucleus for the outermost electrons increase steadily with the atomic number.

Consequence of lanthanoid contraction

1. From lanthanoid to leutetium

If you observed from La to Lu the size is decrease, it mean,

  1. The nuclear charge will increases.
  2. The electron capacity will increases.
  3. Thats why, the electronegativity will also increases.

2. From La to Lu

According to decrease in size from La to Lu, as a result,

  1. Ionisation potential increases.
  2. It mean, the energy required to remove outermost electron is also increases.

3. According to fajan’s rule

Due to this rule,

  1. The polarizing power will also increases.
  2. Due to this, covalent character will also increased.

4. From La to Lu

If look properly about size from La to Lu, the size is decreases, dut to size decreases,

  1. Density increases
  2. Hardness also increases

5. Decreases size from La to Lu

From La to Lu, the size is decreases, and if size is gradually decreases then due to this,

  1. Donating capacity will also decreases.
  2. It mean, it can’t donate.
  3. And reducing capacity will decreases.

5. La (OH)3 > Lu (OH)3

According to Lanthanoid contraction,

  1. La (OH)3 has less basic capacity compare with La (OH)3.
  2. La (OH)3 is act as a best reducing agent compare with Lu (OH)3.

Other consequences of lanthanide contraction

Atomic and ionic size – if atomic number increase then there is regular decrease in size.

Hardness – hardness increases then atomic number is also increases.

Melting and boiling point – melting and boiling point increases on going to La and Lu.

Ionization potential – when ionization potential increases with increases in atomic number.

basicity of oxides and hydroxides – the covalent bond Ln – 0 bond increases, the basic character decrease.

Causes of lanthanide contraction

If the decreasing in the size of lanthanide with an increases in atomic number is known as lanthanide contraction.

for example,

cause of lanthanide contraction

The main cause of lanthanide contraction is, lesser shielding effect of the 4f electrons. but it is better effect in d subshell. due to this, it is considered poor shielding effect in 4f subshell.

The electronic configuration of these elements show that the diffrentiating electrons inter in the f sub energy but not in valency shell. and the screening effect of f electrons is very small.

you know that, if nuclear charge increases when increases in atomic number. Due to this reason, lesser screening effect of f electrons can not reduce the effect of N. C.

As a result, valency electrons are attracted by nuclear with the greater forces.

So we can say that, if atomic and ionic radii is decrease with the increases in the atomic number.

Oxidation state of the elements of the lanthanide series?

If we are talking about oxidation state of lanthanides. lanthanide show variable oxidation state such as +2, +3, and in some matels show +4 oxidation state.

Yes, it is true they also show +2 , +3, +4 oxidation state. there are some metals show +3 oxidation states like,

  1. Samarium
  2. Europium
  3. Ytterbium

Samarium

It is a silvery white chemical elements with the symbol sm.

The atomic number of samarium is 62.

this elements belongs to lanthanide series. this element has oxidation state +3 but this elements also show or exist +1, +2, +3, +4 oxidation state. the electronic configuration of samarium is,

oxidation state of samarium

It is slow oxidizes.

it is used as a catalyst or chemical reagent.

It slowly oxidizes in air.

These type of elements belong to the lanthanide series.

Properties of samarium

properties of samarium

Europium

these type of metals show +3 oxidation state.because europium has atomic no 63. and the electronic configuration of these metals is,

oxidation state of europium

it losses two electron from 6s energy levels. due to this, it make high stability, half fill 4f7 configuration.

Properties of europium

properties of europium

Ytterbium

Ytterbium is also a chemical elements in which

oxidation state of ytterbium

Physical properties of ytterbium

Also some metals show oxidation state such as,

  1. Pr – Praseodymium
  2. Nd – Neodymium
  3. Tb – Terbium
  4. Dy – Dysprosium

These type of metals also show +3 oxidation state.

Question And Answer

1. What is the main diffrence between lanthanoids and actinoids? (Give proper difference)

Lanthanoids

  1. The electronic configuration of lanthanide is
  2. 4f 0-14 5d 0-1 6s2.
  3. They show only +2 , +3, +4 oxidation states.
  4. They show colourless ions (unpaired electrons).
  5. Difficult to form complexes.
  6. They do not form oxo cation.
  7. Complexes are less basic.
  8. They non radioactive.
  9. Paramagnetic character will be explain easily.
  10. Last electrons inter in 4f orbitals.
  11. Lanthanide occur in nature except promethium. (synthetic elements).

Actinoids

  1. The electronic configuration of actinoids is 5f0-14 6d0-1 7s2.
  2. Last electrons inter in 5f orbitals.
  3. They show +2 to +7 oxidation states.
  4. They do not show colourless ions.
  5. They easily form complexes.
  6. They form oxo cation.
  7. Complexes are more basic.
  8. All are radioactive.
  9. Paramagnetic character do not explain easily.
  10. Actinoids are prepared in laboratory and except uranium and therium.
2. What is lanthanide contraction bsc 2nd year?

In lanthanide series, when you move to form left to right the size of these elements decreases continously. this conditions of lanthanide is know as lanthanide contraction.

Decrease in size of lanthanide with the increasing atomic number is known as lanthanide contraction.

3. What is lanthanoids contraction and Actinoides contraction?

Lanthanoids contraction – the regular decreases (contraction) in the size of the atoms and ions with increasing atomic number. this is know as lanthanoids contraction. lanthanoids are filling in 4f orbitals and size contraction of lanthanoids are more.

Actinoids contraction – the gradual decreases in the ionic radii with the increases in atomic number. this is called actinoids. and in this case, it filling in 5f orbitals.

4. What is lanthanide electrons configuration?

Lanthanide electron configuration is, 4f0-14 5d0-1 6s2.

5. What is Actinide?

The first elements of actinide series is actinium. due to this actinide is define as it is first elements of actinide series. the symbol of actinium is An.

An elements in actinide series, range from atomic number 89 to 103. this type of elements come in actinide series. this is called actinide.

This type of elements is radioactive in nature and gives more energy.

Uranium and thorium is the best example of actinide. both are best example for actinide series.

The genral electronic configuration of actinide is [Rn] 5f0-14 6d0-1 7s2.


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