Q9 of 59 Page 27

the elements in which electrons are progressively filled in 4f-orbital are called

Lanthanoid are known for their 4 f orbitals so the electrons are also filled in these orbitals.

For example, [Xe] 4f7 5d1 6s2= Electronic Configuration of Gadolinium


This is an element present iin the lanthanoid series and has electrons present in the 4f orbitals.


(Diagram of Lanthanoids).

More from this chapter

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7

Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is:

 8

The period number in the long form of the periodic table is equal to

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Which of the following is the correct order of size of the given species:

 11

The formation of the oxide ion, O2– (g), from oxygen atom requires first an exothermic and then an endothermic step as shown below:

O (g) + e– → O– (g) ; ∆ Hς = – 141 kJ mol–1


O– (g) + e– → O2– (g); ∆ Hς = + 780 kJ mol–1


Thus process of formation of O2– in gas phase is unfavourable even though O2– is isoelectronic with neon. It is due to the fact that,