Question

Total number of possible shells in an Uranium atom is (Atomic No= 92).
A) 7
B) 1
C) 6
D) None of these

Answer 1

Hint: Uranium belongs to f-block elements.
In each orbital there can only be 2 electrons with opposite spin.

Complete answer:
The question is asked for the total number of possible shells in Uranium atoms with atomic number 92.
The shells are considered as the orbit around the nucleus of an atom consisting of electrons.
The shells are a combination of subshells and the subshells are a combination of orbitals containing one or two electrons with opposite spin.
In quantum mechanics, the location of the electrons or the position of electrons are given using four quantum numbers –
Principal quantum numbers which gives the shell in which electron is present
Azimuthal or angular quantum number which gives the subshell in which electron is present,
Magnetic quantum number gives the orbital and
Spin quantum number gives the spin of the electron.
The quantum numbers are said as the address of an electron as an address defines the location of a house, the quantum numbers give the entire idea about in which shell, subshell or orbital is present in and in which spin state the electron is present in.
Here to solve the question we have to write the electronic configuration of the element.
For writing the electronic configuration we should know the basic ideas of how much subshells are there in shells and how much orbitals are there in subshells.
With the help of equations in quantum mechanics we could trace how much shells, subshells and orbitals are present.
-n is the number of shells present in an atom, it is a positive integer having values 1, 2,3 etc. and they are called as the principal quantum number
-l or azimuthal quantum number will have a value from l to (n-1)
If l=0, then the sub-shell will be s
If l=1 then, subshell notation is p, for l=2 is d, l=3 is f so on.
And the number of subshells is equal to n.
Magnetic quantum number gives the number of orbitals present in an atom, and can have values from –l to +l
m = -l to +l
There are 1 orbital in s subshell, 3 orbitals in p subshell, 5 orbitals in d subshell, 7 orbitals in f subshell etc.
For example if n is 3, then l=1, m=0, and S=$+\dfrac{1}{2}$, then the electron is in $3{{p}_{y}}$
The energy order in which the electrons should be filled is in the order,
1s,2s.2p,3s,3p,4s,3d,4p,5s,4d,5p,4f,5d,6p,7s,5f,6d,7p etc.
There can only be a maximum of 2 electrons in an orbital.
Now let’s write the configuration of Uranium, there are 92 electrons and lets distribute 92 electrons in each orbital in the increasing of energy,
\[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{2}}3{{d}^{10}}4{{p}^{6}}5{{s}^{2}}4{{d}^{10}}5{{p}^{6}}6{{s}^{2}}4{{f}^{14}}5{{d}^{10}}6{{p}^{6}}7{{s}^{2}}5{{f}^{4}}\]
From the electronic configuration, we know that the value of n=7.

$\therefore $ Number of shell =7, so the correct option is option (A).

Note: The energy order of the filling of electrons must be known, to solve every problem related to the electronic configuration. We must know the quantum numbers and no orbital could accommodate more than 2 electrons.
We should clearly know about what all subshells, orbitals that are present in an atom if n (principal quantum number) is given, or they may give the azimuthal quantum number and ask to find the other quantum numbers which give the orbitals, shells etc.