【 】Why does 19th electron of K (Potassium)go to 4s orbital instead of 3d orbital?

Why does 19th electron of K go to 4s orbital instead of 3d orbital?

Answer:


The 19th electron or last electron of potassium (K) goes to 4s orbital instead of 3d orbital because the energy of 4s orbital is lower than 3d orbital.


Explanation:


According to Aufbau principal,an electron always goes to lower energy level or orbital first,then goes to higher energy levels or orbitals.


The sum of" n+ l "value determines the energy of an orbital.Here, n is the principal quantum number and l is the azimuthal quantum number.

For l=0,we get "s" orbital.

For l=1,we get "p" orbital.

For l=2, we get "d" orbital.

Now determine the energy of 4s and 3d orbitals by applying n+l formula.

For 4s ,n=4 and l=0

              So,n+l is 4+0 =4

For 3d ,n=3 and l=2

              So,n+l is 3+2 = 5

Here,we see that the n+l value for 4s is lower than 3d,so 4s has lower energy than 3d orbital.That is why the 19th electron or last electron of potassium (K) goes to 4s orbital instead of 3d orbital because the energy of 4s orbital is lower than 3d orbital.

●K(19)--->1s2 2s2 2p6 3s2 3p6 3d1(Expected but not correct)

●K(19)--->1s2 2s2 2p6 3s2 3p6 4s1(Correct)