Question

Use an energy-level diagram to show the electron arrangement in the scandium (Sc) atom. The atomic number of Sc is 21. Write an allowed set of quantum numbers ( ) for the highest energy electron.

Answer 1

Energy level diagram is attached.

4 quantum numbers are used to describe a particular electron in an atom.{n,l,m,s}

The electronic configuration of Sc is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹

The highest energy electron resides in 3d orbital.

For 3d orbital Principal quantum number n=3; azimuthal quantum number for d orbital =2

Magnetic quantum number,m_l can be anything from the set{-2,-1,0,1,2}.

Spin can be up or down.Hence +1/2 or -1/2 are possible for s.

Usually electron filling is considered from -ve to + ve m_l value and up spin(+1/2) is allowed to every first electron in an orbital. Pairing of electrons will takes place only after every orbital gets singly occupied. 2 electrons residing at same orbital having all three quantum numbers same will differ by a 4th quantum number (spin, s).

From these considerations, allowed set of quantum numbers for highest energy electron of Sc is {n=3, l=2, m_l=-2, s=1/2}