# Promethium Bohr model

In the promethium Bohr model, the nucleus comprises 61 protons and 84 neutrons. Surrounding this nucleus are six electron shells, accommodating a total of 61 electrons.

To draw the promethium Bohr model, represent the 61 protons, 84 neutrons, and 61 electrons. Begin by sketching the nucleus, and then draw the six electron shells. The first five shells should contain 2, 8, 18, 23, and 8 electrons, respectively, while the sixth shell holds the remaining 2 electrons.

Contents

## Steps

### Find protons, neutrons, and electrons of promethium atom

Promethium has 61 protons, 84 neutrons, and 61 electrons.

#### Promethium protons

• Protons = atomic number

From the periodic table, find the atomic number of promethium.

The atomic number of promethium is 61. Hence, promethium has a total of 61 protons.

#### Promethium neutrons

• Neutrons = atomic mass – atomic number

The atomic mass of promethium is 145 and the atomic number of promethium is 61.

Subtract the atomic number (61) from the atomic mass (145). Hence, promethium has a total of 145 – 61 = 84 neutrons.

#### Promethium electrons

• Electrons = atomic number

The atomic number of promethium is 61. Hence, promethium has a total of 61 electrons.

### Draw nucleus of promethium atom

The nucleus of a promethium atom contains 61 protons and 84 neutrons. So draw the nucleus of promethium atom as follows:

Now in the next step, draw the 1st electron shell and start marking electrons.

### Draw 1st electron shell

Remember that we have a total of 61 electrons.

The 1st electron shell (containing s subshell) can hold up to a maximum of 2 electrons. So draw the 1st electron shell as follows:

In the above image, 1 represents the 1st electron shell that contains 1s subshell. And the green color represents the number of electrons in that subshell. This means that the 1st electron shell has a total of 2 electrons.

Since we have already used 2 electrons in the 1st electron shell, now we have 61 – 2 = 59 electrons left. So in the next step, we have to draw the 2nd electron shell.

### Draw 2nd electron shell

The 2nd electron shell (containing s subshell and p subshell) can hold up to a maximum of 8 electrons. So draw the 2nd electron shell as follows:

In the above image, 2 represents the 2nd electron shell that contains 2s and 2p subshells. And the green and orange color represents the number of electrons in that subshell. This means that the 2nd electron shell has a total of 8 electrons.

Now we have already used 10 electrons in 1st and 2nd electron shells, so we have 61 – 10 = 51 electrons left. So in the next step, we have to draw the 3rd electron shell.

### Draw 3rd electron shell

The 3rd electron shell (containing s subshell, p subshell, and d subshell) can hold up to a maximum of 18 electrons. So draw the 3rd electron shell as follows:

In the above image, 3 represents the 3rd electron shell that contains 3s, 3p, and 3d subshells. And the green, orange, and pink color represents the number of electrons in that subshell. This means that the 3rd electron shell has a total of 18 electrons.

Now we have already used 28 electrons in 1st, 2nd, and 3rd electron shells, so we have 61 – 28 = 33 electrons left. So in the next step, we have to draw the 4th electron shell.

### Draw 4th electron shell

The 4th electron shell (containing s subshell, p subshell, d subshell, and f subshell) can hold up to a maximum of 32 electrons. So draw the 4th electron shell as follows:

In the above image, 4 represents the 4th electron shell that contains 4s, 4p, 4d, and 4f subshells. And the green, orange, pink, and blue color represents the number of electrons in that subshell. This means that the 4th electron shell has a total of 23 electrons.

In the 4th electron shell, the 4f subshell has only five electrons. This is because according to the aufbau principle, the 5s subshell is filled first and then 4d, 5p, 6s… and so on.

Now we have already used 51 electrons in 1st, 2nd, 3rd, and 4th electron shells, so we have 61 – 51 = 10 electrons left. So in the next step, we have to draw the 5th electron shell.

Still have a question: Why does the 4f subshell have only five electrons?

Let’s draw the orbital diagram of promethium, and find the answer to the above question.

Answer: Once the 6s subshell is completely filled, then only we can mark electrons in the 4f subshell. That’s why in the 4th electron shell, the 4f subshell has only five electrons.

### Draw 5th electron shell

The 5th electron shell can hold up to a maximum of 50 electrons. So draw the 5th electron shell as follows:

In the above image, 5 represents the 5th electron shell that contains 5s and 5p subshells. And the green and orange color represents the number of electrons in that subshell. This means that the 5th electron shell has a total of 8 electrons.

The 5th electron shell contains only 5s and 5p subshells, and not 5d and 5f subshells. This is because according to the aufbau principle, the 6s subshell is filled first and then 4f, 5d, 6p… and so on.

Now we have already used 59 electrons in 1st, 2nd, 3rd, 4th, and 5th electron shells, so we have 61 – 59 = 2 electrons left. So in the next step, we have to draw the 6th electron shell.

### Draw 6th electron shell

The 6th electron shell can hold up to a maximum of 72 electrons. So draw the 6th electron shell as follows:

In the above image, 6 represents the 6th electron shell that contains 6s subshell. And the green color represents the number of electrons in that subshell. This means that the 6th electron shell has a total of 2 electrons.

That’s it! This is the final Bohr model of promethium atom as we have used all 61 electrons: 2 electrons in the 1st electron shell, 8 electrons in the 2nd electron shell, 18 electrons in the 3rd electron shell, 23 electrons in the 4th electron shell, 8 electrons in the 5th electron shell, and 2 electrons in the 6th electron shell.

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