Why does 4s orbital have low energy than 3d orbital?

Answer 1

that's not a proper question i guess..

it's an obvious thing that it's having less energy that's why it's lower energy level while 3d is having more energy than 4s.

Don't go on the numbers 3 and 4. you might be thinkning 3 comes before 4 so 3 should be filled firstly but it's not like that.........

we follow here Aufbau priniple which state that shell having less energy will be filled firstly will electron and then electrons will enter in the higher energy orbit......

Answer 2

They aren't. What you probably mean to ask is why are 5d orbitals filled before 4f orbitals, and the reason is despite the numbers, electrons always occupy the level that requires the least-energy first, as stated in the aufbau principle. In this case, the 5d orbtial requires less energy than the 4f orbital, so it is filled before the 4f orbital. The same can be said for the reason why 4s orbitals are filled before 3d orbitals, which may be what you were asking about.

Answer 3

The reason why the energy of 4s is less than 3d in a multielectron atom of irons has to do with the distance from the nucleus. The closer they are to the nucleus, then the more electron density they will have.

Answer 4

I'm not sure I can give you a better answer than "because that's how reality works." There's not some deep secret here ... it's just the way things are. It all makes sense according to the math, but the math is a little complicated, and rather than try to represent it here I will just suggest you find any good book on quantum mechanics (Levine's Quantum Chemistry is my go-to reference) and try to follow along.

If it helps any, the energy difference between s orbitals gets smaller as the principal quantum number increases; the gap between 1s and 2s is bigger than the gap between 2s and 3s which is in turn bigger than the gap between 3s and 4s. The gaps between orbitals within a principal quantum number also get smaller as the principal quantum number gets larger, but there are more of them, so they add up: the gap between 3s and 3p is less than the gap between 3s and 4s, but when you also add in the gap between 3p and 3d the total winds up being more than that between 3s and 4s.

Answer 5

This is true only up until calcium, then from scandium onwards, the 4s is higher in energy than the 3d. The reasons are more complex than easily explained here. It has to do with effective nuclear charge, repulsion of electrons by one another, and a host of other complex factors.

Answer 6

The 4s orbital has a lower energy than the 3d orbital due to shielding effects and penetration of electrons. Electrons in the 4s orbital experience more shielding from inner electrons and have higher penetration into the nucleus, resulting in a lower energy level compared to the 3d orbital.

Answer 7

its not less energy its actually higher energy..it contains 14 electrons as oposed to 5d (10 electrons)