Bohr model of Arsenic Atom-How to draw Arsenic (As) Bohr-Rutherford diagram?

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The Bohr Model of Arsenic (As) has a nucleus that contains 42 neutrons and 33 protons. This nucleus is surrounded by four electron shells namely K-shell, L-shell, M-shell, and N-shell. The 1st shell has 2 electrons, the 2nd shell has 8 electrons, the 3rd shell has 18 electrons and the 4th shell contains 5 electrons.

NameArsenic Bohr Model
Number of neutrons42
Number of protons33
Number of electrons33
Total electron shells
Electron in the First shell(K)2
Electrons in the Second shell(L)8
Electrons in the Third shell(M)18
Electrons in the Fourth shell(N)5
Total valence electrons in Arsenic5

How to draw Bohr Model of Arsenic (As)?

Bohr model describes the visual representation of orbiting electrons around the small nucleus. It used different electron shells such as K, L, M, N…so on. These shells hold a specific number of electrons, the electron shell which is closest to the nucleus has less energy and the electron shell which is farthest from the nucleus has more energy.

Bohr’s diagram is very interesting and easy to draw. Here, we will draw the Bohr model of the Arsenic atom with some simple steps.

Steps to draw the Bohr Model of Arsenic atom

1. Find the number of protons, electrons, and neutrons in the Arsenic

Protons are the positively charged particles and neutrons are the uncharged particles, both these are constituents of the atom nuclei. Electrons are the negatively charged particles that orbit the nucleus of an atom

To find the number of protons an atom contains, just look at its atomic number.

If the atomic number of atom is 45, then proton will also be 45, if atomic number is 46, then proton will also be 46.

As the atomic number of Arsenic is 33 so the number of protons present in it is also 33.

number of protons in arsenic

Now, to determine the number of neutrons in an atom, use this formula.

⇒ Number of neutrons in atom = Atomic mass of the atom(rounded to the nearest whole number) – Number of proton in an atom

For example, An atom have 33.988 atomic mass and 16 protons.

Then, to find the number of neutron, round the atomic mass to the near whole number, so, atomic mass 33.988 round to 34.

= (34 – 16 protons) = 18 number of neutrons in the atom

Now, to get the number of neutrons in an Arsenic atom, look at its atomic mass which is 74.922, rounded off to the nearest whole number it is 75. The number of protons present in Arsenic is 33.

∴ Hence, the number of neutrons in Arsenic atom = (75 – 33) = 42.

number of neutrons in arsenic bohr model

It should be noted that “The number of electrons in a neutral atom is equal to the number of protons”.

As the Arsenic (As) atom is neutral thus the number of electrons present in it will be equal to its number of protons i.e., 33, as we discussed earlier.

⇒ The number of electrons in an Arsenic atom = 33

⇒ The number of protons in the Arsenic atom = 33

⇒ The number of neutrons in an Arsenic atom = 42

Let’s read in detailHow to find number of protons, electrons, neutrons?

2. Draw the nucleus of an atom

A nucleus is a dense and small region that contains the number of protons and neutrons of an atom.

In this step, we have to draw a small circle that consists of a number of protons and the number of neutrons of an Arsenic atom.

nucleus of arsenic bohr diagram

3. Draw the First electron shell

“An electron shell may be thought of as an orbit followed by electrons around an atom’s nucleus.”

The first electron shell is also called the K-shell, this is the closest shell to the nucleus of an atom and can hold a maximum of two electrons.

As we identified, the Arsenic atom has a total of 33 electrons. So we need to put 2 electrons from the 33 available in the first shell, next to each other, as shown below.

1st electron shell of arsenic

Now, that we have successfully drawn the first shell of the Arsenic atom that can hold 2 electrons, we know that we have used 2 electrons out of the 33 available in the first shell.

(33 – 2) = 31 electrons.

This shows we are left with 31 electrons that we need to accommodate in the subsequent shells of the Arsenic atom.

4. Draw the Second electron shell

The second shell also called the L-shell that can hold a maximum of 8 electrons. This shell is drawn after the first electron shell.

In the second electron shell, the electrons are added one at a time, starting from the top position and then going in a clockwise direction.

In second shell, electrons are added one at a time in clockwise direction as a clock position – 12 o’clock, 3 o’clock, 6 o’clock, 9 o’clock positions.

electrons placing position in bohr diagram

Once you place the electrons one at a time to each of the four sides(Top – Right – Bottom – Left], start pairing or doubling them.

As we have 31 remaining electrons of an Arsenic atom, out of which the second shell can hold only a maximum of 8 valence electrons.

Thus, we place the next 8 electrons of the Arsenic atom in the second shell. Start from the top position and put electrons one at a time, moving in a clockwise direction (Top-Right-Bottom-Left), and finally pair them up.

2nd electron shell of arsenic bohr model

At this step, out of the 33 electrons of the Arsenic atom, we have placed 2 electrons in the first shell and 8 electrons in the second shell.

[33 – (2+8)] = 23 electrons.

This means we are now left with 23 electrons. So let’s see how we can assign them their appropriate positions in the next shells of the Arsenic atom.

5. Draw the Third electron shell

The third electron shell also called the M-shell can accommodate up to 18 electrons. For the elements in the first few periods of the Periodic Table, the third shell holds up to 8 electrons only. But actually, in totality, it has the capacity to hold 18 electrons.

⇒ The third subshell exhibits this capacity of holding ‘up to 18’’ electrons for atomic numbers greater than 20 such as 21, 22, 23, 24 and so on.

⇒ The atomic number of Arsenic (As) is 33. As 33 is visibly greater than 20, this means the M-shell in the Arsenic Bohr model will be filled to its maximum capacity by accommodating a total of 18 electrons, as shown below.

The electrons are placed in a clockwise manner, as we discussed in step 4. Starting from the top position, put the electrons one at a time while moving in a clockwise direction (Top-Right—Bottom-Left), before pairing up the electrons.

3rd electron shell of arsenic bohr diagram

By the time we have reached this step, out of the 33 electrons of the Arsenic atom, we have placed 2 electrons in the first shell, 8 electrons in the second shell and 18 electrons in the third electron shell which means a total of 2+8+18 = 28 electrons are used so far.

33 – [ 2+ 8+ 18] = 33 – 28 = 5 electrons.

Thus, the remaining 5 electrons then go into the fourth shell of the Arsenic Bohr model.

6. Draw the Fourth electron shell

The 5 electrons are filled in the Fourth electron shell of the Arsenic Bohr model, again following the clockwise pattern of placing electrons, as shown below.

4th electron shell of arsenic bohr model

Now, 4th shell has a total of 5 electrons.

bohr model for arsenic (As)

And here we have the accurate Bohr model of the Arsenic atom that contains 33 protons and 42 neutrons in the nucleus region while a total of 33 electrons circulate around the nucleus in specific orbits called shells.

The first electron shell of Arsenic has two electrons, there are eight electrons in the second shell, eighteen electrons in the third shell, and five electrons in the fourth shell of Arsenic (As).

Also Read:-

Also check :- Bohr model for all elements of Periodic table

FAQ

What is the Bohr diagram?

The Bohr diagram formally called a Bohr-Rutherford model is a visual representation of orbiting electrons around the small nucleus of an atom. For example, the Bohr diagram of Arsenic (As) represents the 33 electrons present in it, revolving around the small nucleus in specific energy levels called K, L, M, and N shells.

How many electron shells an Arsenic Bohr model contains?

Electron shells are also called energy levels. You can find the number of electron shells for an element by knowing its period number in the Periodic Table.

The elements or atoms in the first period of the Periodic Table have one energy level or one electron shell, similarly, the elements in the second period have two energy levels or two electron shells, and so on.

As the Arsenic (As) atom belongs to the 4th Period in the periodic table, hence the number of electron shells for the Bohr model of Arsenic is also 4. There are 4 electron shells in the Arsenic Bohr model namely K-shell, L-shell, M-shell, and N-shell.

What is the outer shell of the Bohr diagram of the Arsenic atom?  

The outermost shell also called the valence shell is the shell that contains the valence electrons of an atom.

According to the Bohr diagram of Arsenic, its outer shell is shell number 4 i.e., the N-shell containing 5 valence electrons.

Summary

  • The Bohr model of Arsenic (As) is drawn with four electron shells, the first shell contains 2 electrons, the second shell contains 8 electrons, the third shell contains 18 electrons and the fourth shell contains 5 electrons.
  • The atomic number of Arsenic is 33. As Arsenic (As) is a neutral atom hence the number of protons and electrons available for its Bohr diagram are equal i.e., 33.
  • The number of neutrons for the Bohr diagram of Arsenic can be found by subtracting the number of protons from the atomic mass (rounded off to the nearest whole number).
  • The electron configuration of Arsenic in terms of the shells is [2, 8, 18, 5] while in the standard form it is [Ar] 3d10 4s2 4p3.

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