Question

How many 4d electrons would be predicted in the ground state for the following elements?a. zirconiumb. cadmiumc. iridiumd. iron

Answer 1

In order to answer the question first we must write the atomic number of each element:

Zirconium (Zr): 40

Cadmium (Cd): 48

Iridium (Ir): 77

Iron (Fe): 26

Then, we have to complete the distribution of electrons in each orbital for each atom:

The first 4 levels have the following distribution:

Level1: 1s

Number of electrones: 2

Level 2: 2s, 2p

Number of electrones 8 (2 in the s orbital and 6 in the p orbitals).

Level3: 3s, 3p, 3d

Number of electrones 18 (2 in the s orbital, 6 in the p orbital and 10 in the d orbitals)

Level 4: 4s, 4p, 4d, 4f

Number of electrones 32 (2 in the s orbital, 6 in the p orbitals, 10 in the d orbitals and 14 in the f orbitals)

The order in which the orbitlas are completed depends on the energy of each level. For example the 4s orbitals will be completed before the 3d orbitals because their energy is lower.

The order is as follows:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p...

Now, knowing the atomic number we can answer the question:

For Zirconium (total 40 electrones):

`1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3d^(10),4p^6,5s^2,4d^2`

2 electrones are predicted in the 4d orbital

For Cadmium (total 48 electrones):

`1s^2,2s^2,2p^6,3s^2,3p^6,4s^2,3d^(10),4p^6,5s^2,4d^(10)^{}`

10 electrones are predicted in the 4d orbital

For iridium, as it has an atomic number higher than Cadmium we can predict tha it also complets the 4d orbital, then it has also 10 electrones in it.

For iron (total 26 electrones)

`1s^2,2s^2,2p^6,3s^2,3p^64s^2,3d^6`

Iron has no electrones in the 4d orbitals