# Orbital Craziness: 4s, 3d, 4p - Why 3d?

• ShawnD
In summary, the fourth period of elements go 4s, 3d, 4p because the 4s orbital has a lower energy than the 3d orbital.
ShawnD
When looking at the orbital names, why does the fourth period of elements go 4s, 3d, 4p? Why is it 3d? Why not 4d?

It is because the 4s orbital happens to have a lower energy than the 3d orbital. If you notice on the periodic table, you do not start getting the transition metals until the 4th period due to this. If you want to know why the 3d orbital has a higher energy than the 4s, well you need three semesters of university level physics for that.

Orbital filling gets even more complicated than than when you start filling up the d and f orbitals. In the lanthanide series, for instance, Ceriium with an atomic number of 58, has the orbital strucutre [Xe] 4f1 5d1 6s2, but Praseodymium, with an atomic number of 59, has the structure [Xe] 4f3 6s2! So there are general rules for the lower orbitals but things start getting crazy as you get the higher energy orbitals.

To understand it concretly, you need to know Quantum Physics properly (as so-crates has mentioned). For now, you can remember that as a general rule, of two subshells, the subshell with a lower value of (n+l) where n = principal quantum number of the shell and l = azimuthal/angular momentum quantum number, is filled first. For 4s, n+l = 4 (as n = 4 and for the s-subshell, l = 0) and for 3d, n+l = 3 + 2 = 5. So 4s is filled before 3d.

In case the value of n+l is equal for two subshells, the subshell having a lower value of the principal quantum number is filled first. This pretty much sums up what is called the Aufbau Principle. It seems hardly convincing at first and the actual reason can be explained convicingly only using quantum physics.

Hope that helps...

Cheers
Vivek

And as far as the Qunatum Mechanics goes, if you solve for the radial part of the wavefunction, you find that the Enegry Eigenstates go like : (if this makes no sense, ignore it and simply look at the line below)

E(n,l) = -E1/(n+l)^2

This is what maverick was talking about - "The energy increases with increasing (n+l)".

Additional Note : Remember, l = 0, 1, 2, and 3 are respectively designated the labels s, p, d, and f.

By the way, do you happen to know that the designations s, p, d, and f come from sharp, principal, diffuse, and fundamental, respectively?

## What is orbital craziness?

Orbital craziness refers to the phenomenon observed in atoms where electrons occupy energy levels in a seemingly chaotic manner, rather than following a predictable pattern.

## What are 4s, 3d, and 4p orbitals?

4s, 3d, and 4p are different types of orbitals, or regions in an atom where electrons are most likely to be found. The numbers indicate the energy level, or shell, in which the orbital is located, and the letter indicates the shape of the orbital.

## Why is the 3d orbital significant in orbital craziness?

The 3d orbital is significant because it is the first orbital in the d subshell and is located at a higher energy level than the 4s and 4p orbitals. This leads to complex interactions between electrons in the 3d orbital and those in the outer orbitals, resulting in orbital craziness.

## How does orbital craziness affect chemical properties?

The orbital craziness observed in atoms can affect their chemical properties by making it more difficult to accurately predict the behavior of electrons. This can lead to unexpected chemical reactions and the formation of new compounds.

## What factors contribute to orbital craziness?

There are several factors that contribute to orbital craziness, including the number of electrons in an atom, the energy levels and subshells of the orbitals, and the repulsion and attraction between electrons. All of these factors can lead to chaotic electron behavior and result in orbital craziness.

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