Question

Is the energy of an electron in 2s orbital same as of that in 2p orbital? Why?

Answer 1

for hydrogen atom the energy of an electron in 2s orbital is same as that in 2p orbital but for multi electron atoms the energy of electron is decided by its principal quantum number and azimuthal quantum number.

for multi electron atoms we follow (n + l) rule which says that electron with least (n + l) value has lowest energy and if both electrons have same l the electron with least n has lowest energy.

applying (n + l) rule for 2s we get the value = 2 + 0 = 2

and for 2p we get the value = 2 + 1 = 3

so electron in 2p orbital has more energy than electron in 2s orbital.