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Question

The element potassium has an atomic number 19 and a mass number is 39. Give the number of electrons, protons, and neutrons in it. Give the electronic configuration in different energy shells. Mention its valency.


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Solution

Given:

Atomic number of Potassium (K)=19

Mass number of Potassium (K)=39

Formula:

  1. Atomic number=Number of electrons=Number of protons
  2. Mass number=Number of protons+Number of neutrons

Calculate the number of electrons in Potassium atom (K):

Number of electrons=Atomic number

Thus,

Thus, the number of electrons in Potassium is 19.

Calculate the number of protons in Potassium atom (K):

Number of protons=Atomic number

Thus,

Thus, the number of protons in Potassium is 19.

Calculate the number of neutrons in Potassium atom (K):

Mass number=Number of protons+Number of neutrons

Number of neutrons=Mass number-Number of protons

Number of neutrons=39-19=20

Thus, the number of neutrons in Potassium is 20.

Electronic configuration of Potassium atom (K):

  1. The number of electrons in Potassium is 19.
  2. In the potassium atom, the first shell i.e. K shell will hold 2 electrons, the second shell i.e. L shell will hold 8 electrons. Thus, 10 electrons are filled.
  3. Now, the third shell i.e. M shell is expected to hold the remaining 9 electrons.
  4. But according to Bohr Bury scheme, the outermost shell cannot have more than 8 electrons.
  5. Thus, the third shell i.e. M shell will hold 8 electrons and the 1 remaining electron goes to the fourth shell i.e. N shell.
  6. Thus, the electronic configuration becomes (2,8,8,1).

Thus, the electronic configuration of Potassium atom (K) is (2,8,8,1).


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