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Question

The atom of an element has 20 protons, 20 neu­trons, and 20 electrons. Find out its electronic configuration mentioning the shell.


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Solution

Given:

Number of protons=20

Number of neutrons=20

Number of electrons=20

Formula used:

Atomic number=Number of protons=Number of electrons

Find the atomic number of the element:

Atomic number=Number of protons=Number of electrons

Atomic number=20

Thus, the atomic number of the element is 20.

Find the name of the element:

The element with atomic number 20 is Calcium (Ca).

Thus, the name of the element is Calcium (Ca).

Write the electronic configuration of Calcium:

  1. The distribution of electrons in various energy levels or shells of an atom of the element is known as its electronic configuration.
  2. The total number of electrons in Calcium atom is 20.
  3. Starting from the nucleus, the first shell i.e.K shell holds 2 electrons, the second shell i.e.L shell holds 8 electrons. Thus, 10 electrons are filled.
  4. Now, the third shell i.e. M shell is expected to hold the remaining 10 electrons.
  5. But according to Bohr Bury scheme, the outermost shell cannot hold more than 8 electrons.
  6. Thus, the M shell holds 8 electrons and the remaining 2 electrons go into the fourth shell i.e. N shell.
  7. Thus, the electronic configuration is (2,8,8,2).

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