Potassium has the atomic number 19 and is represented by the chemical symbol K. It is a very soft metal and can even be cut into pieces using a knife. It is silvery-white in appearance and is known to react vigorously with water.
Potassium ions are known to play a vital role in our body such as nerve transmission and deficiency of potassium may result in abnormal heart rhythms. It is also used commercially, especially in soap and fertilizer industries.
Hello friends, in this article we will learn about potassium and its Bohr model.
So let’s begin…
Bohr Model of Potassium
Atoms were earlier regarded as microscopic structures that had a heavy core, known as the nucleus, that carried a positive charge, and electrons traveled around the nucleus in random orbits.
In 1915, Niel Bohr modified the previous model proposed by Ernst Rutherford and established that the electrons travel around the nucleus in definite circular orbits, also known as shells. Also, Bohr stated that these shells have definite energy levels.
Basically, Rutherford focused on explaining the nucleus of the atom while the electrons, as well as their positions and energies, were described by Bohr.
He labeled these shells by integers, the quantum number n, where n can be any value viz. 1, 2,3, 4, etc. Also, these shells can be named in alphabetical order as K, L, M, N, etc.
This model also emphasizes the fact that electrons are able to move from one shell to another. The loosing of energy by an electron causes it to drop down to a shell with lower energy while the gaining of energy results in the jumping of electrons from lower to higher energy levels.
Therefore, the postulates of the Bohr-Rutherford model are as follows:
• The maximum mass of an atom is concentrated at its center, also known as the nucleus, which consists of protons and neutrons.
• Protons are positively charged atomic species while neutrons do not carry any charge.
• Electrons are negatively charged and travel around the nucleus in defined orbits or orbital shells that have fixed energy.
• These orbital shells are represented using the integer n (where the value of n can be any whole number viz. 1, 2, 3, 4, etc.)
• The electrons can move from lower to higher energy orbitals by gaining energy and from higher to lower energy orbitals by losing energy.
The farthest shell from the nucleus that carries electrons is known as the valence shell, and the electrons housed in this shell are known as the valence electrons.
In the case of the Potassium atom, there are 19 protons, 20 neutrons, and 19 electrons. The electrons are housed in four shells i.e. K, L, M, and N shells.
|No. of Proton||19|
|No. of Neutron||20|
|Number of Electron||19|
|Number of shells||4|
|Number of electrons in first (K) shell||2|
|Number of electrons in second (L) shell||8|
|Number of electrons in third (M) shell||8|
|Number of electrons in fourth (N) shell||1|
|Number of valence electrons||1|
Drawing Bohr Model of Potassium
Potassium is a member of group 4 and Period 1. It is the 19th element of the Periodic table.
The information that we can infer from the above-mentioned Potassium box is as follows:
• The atomic number of Potassium is 19.
• The electronic configuration of Potassium is [Ar] 4s1.
• The atomic symbol of Potassium is K.
• The atomic mass of Potassium is 39.0983.
This information is sufficient to help us draw the Bohr model of Potassium.
To begin with, we will draw the nucleus of this atom.
For this, we will have to find out the number of protons and neutrons in this atom.
The atomic number of an atom and the number of protons inside its nucleus is the same.
In the case of the Potassium atom, the atomic number is 19.
Therefore, the number of protons in the Potassium atom = atomic number = 19.
Now, we will find out the number of neutrons in this atom.
In an atom, the number of neutrons can be calculated by rounding up the atomic mass to its nearest whole number and then, subtracting the number of protons from it.
Therefore, in an atom,
No. of neutrons = Rounding up atomic mass to nearest whole number – No. of protons
The atomic mass of potassium is 39.0983, rounding it up, we get 39.
Also, the number of protons in the Potassium atom, as calculated above, is equal to 19.
Number of neutrons in the Potassium atom = 39 – 19 = 20
Hence, the number of neutrons in the Potassium atom = 20
As these two atomic species reside inside the nucleus, based on this information we can now draw the nucleus of the Potassium atom, which is as follows:
In the above figure, protons are symbolized with p+, and neutrons are symbolized with n°.
As the nucleus of our atom is now complete, we can move on to calculate the number of electrons in the Potassium atom.
For an atom, the number of protons and electrons is always equal.
Therefore, in the case of the Potassium atom,
Number of protons = Number of electrons = 19 e–
The electrons are represented with the symbol e–.
After we have calculated the number of electrons in an atom we will have to accommodate them in their respective energy levels or orbital shells.
For this, we must first understand certain rules that are given below:
• The first shell i.e. K shell always contains only 2 electrons.
• The numbers of electrons in a shell are calculated using the formula 2n2.
• The electrons in any shell, having more than four electrons, are always filled in the group of four in a clockwise manner.
• The first four electrons filled in any shell are placed at an angle of 90° from its descending electron.
• However, this angle between the electrons keeps on decreasing as the number of electrons increases.
Now, we can begin filling these electrons in the shells. Let us begin with K shell.
Number of electrons in the K shell of the Potassium atom = 2n2 = 2
Now, we will move towards the L shell of the Potassium atom.
First, we will calculate the number of electrons in the L shell as per the formula given above.
Therefore, number of electrons in the L shell of the Potassium atom = 2n2 = 2(2)2 = 8
We will now fill these electrons in the group of 4 in the clockwise direction, as mentioned in the rules given above.
Now, that the four electrons are settled in the L shell, we can fill the remaining four electrons in the same manner. After doing this, the shell appears as follows:
So, we now have a complete L shell of the Potassium atom. Therefore, we can move forward to M shell.
The number of electrons in the M shell of the Potassium atom = 2n2 = 2 (3)2 = 18
Therefore, the M shell is expected to hold up to 18 electrons.
However, here is an interesting fact. The initial elements of the periodic table i.e. the elements up to atomic number 20 can only house 8 electrons in their M shell.
Beyond atomic number 20, the atoms are allowed to accommodate any number of electrons below 18 i.e. the maximum electrons that M shell of these atoms can carry is 18.
Hence, the M shell of the Potassium atom contains only 8 electrons.
Now, we will fill these electrons in the M shell, as per the rules given above i.e. in the group of 4 in a clockwise manner.
After filling the first four electrons in the M shell of the Potassium atom appears as follows:
Now, that the four electrons are settled in the M shell, we can fill the remaining four electrons in the same manner. After doing this, the shell appears as follows:
So, we now have a complete M shell of the Potassium atom. Therefore, we can move forward to N shell.
The number of electrons in the N shell of the Potassium atom = 2n2 = 2 (4)2 = 32
Therefore, the N shell of an atom is capable of holding 32 electrons.
However, in the case of potassium atom, we have already filled 2 + 8 + 8 i.e. 18 electrons in the K, L, and M shell, respectively.
As the total number of electrons in the Potassium atom is 19, hence, we are only left with 1 electron.
We will accommodate this electron in the N shell of the Potassium atom after which the final Bohr model of Potassium appears as follows:
Hence, the final Bohr model of the Potassium atom consists of 19 protons, 20 neutrons, and 19 electrons. The electrons are housed in four shells i.e. K, L, M, and N shells as 2, 8, 8, and 1, respectively.
Deriving Lewis Structure from Bohr Model
Both Lewis structure and Bohr model of an atom describes its structure through visual representation.
The only difference is that the Bohr model explains all the details viz. number of protons, neutrons, and electrons, number of shells, etc. while the Lewis structure only displays the valence electrons and nucleus.
Also, the Lewis structure exhibits the electrons in the form of dots while the nucleus is represented with the atomic symbol of that element.
The Lewis structure of Potassium is given below:
The final Bohr model of the Potassium atom consists of 19 protons, 20 neutrons, and 19 electrons.
The electrons are housed in four shells i.e. K, L, M, and N shells as 2, 8, 8, and 1, respectively.
The M shell of atoms having an atomic number below 20 can hold only 8 electrons in their M shell. Therefore, the M shell of the Potassium atom only has 8 electrons.