The last electron in an element 'X' enters the 7s orbital . Write its electronic configuration and find out its atomic number. What is its atomic number ?

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Solution

Dear Student,

The filling of electrons occurs in increasing order of energy according to Aufbau's Principle.
Last electron enters 7s-orbital
Order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s¹
Adding all the electrons, atomic number Z = 87
The element is Francium (Fr)

Regards

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