Question

The electronic configuration of the two outermost shells of an atom is $3{s^2}3{p^6}3{d^5}4{s^2}$What is this atom?
A) Manganese
B) Phosphorus
C) Strontium
D) Vanadium

Answer 1

Hint: The order in which electrons are filled in the orbital is determined by Aufbau principle. This principle states that the order in which electrons should be filled in orbitals is as follows: 1s, 2s,2p,3s,3p,4s,3d and so on.

Step by step explanation:
Step 1: Write the complete electronic configuration.
According to question the complete electronic configuration is$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^5}4{s^2}$
Step2: Count the number of electrons.
The number of electrons in above configuration is 25.
Step3: Identify the element with atomic number equal to number of electrons in the electronic configuration.
Element with atomic number 25 is manganese.

Option A is the correct one.

Additional information: there are 4 rules by which electrons are filled in an orbital. First is, lowers energy orbitals are filled first. Hence, the filling pattern was given above. Second is, orbitals in the subshell are of similar energy. Hence, electrons in similar energy are filled first with parallel spin and then pairing of electrons is done. Lastly, the Pauli exclusion principle states that no two electrons can have the same set of all 4 quantum numbers. In other words, electrons in the same orbital must have opposite spin.

Note: The electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals. Atomic number of phosphorus is 15, the atomic number of strontium is 38 and the atomic number of vanadium is 23.