Question

1. State the electronic configuration of sodium based on the diagram given.
2. What is its atomic number and valency?
3. Label the following in the diagram.

Different energy shells, valence shell, valence electrons

Answer 1

1. The electronic configuration of an element describes how electrons are distributed in its atomic orbitals.

• The electrons are filled in the increasing number of shells viz. K,L,M,N,etc.
• Number of electrons in a shell is given by 2n² where n is the number of shells.
• Putting n=1,2,3 and 4, we get the number of electrons 2,8,18,32 that can be filled in each shell respectively.
• Electronic configuration-
• From the diagram given we can write the electronic configuration of sodium.
• 2 electrons will fill the first shell i.e., the K shell.
• 8 electrons will fill the second shell i.e., the L shell.
• 1 electron will enter the third shell i.e., the M shell.
• The electronic configuration of Sodium will be 2,8,1.

2. Atomic number(Z)- The total number of protons in the nucleus of an atom gives us the atomic number of that atom.

• For a neutral atom the number of protons is equal to the number of electrons.
• Since, the atom has 11 electrons it has 11 protons.
• So, the atomic number of given atom i.e., sodium is 11.
• Valency- Valency is the combining capacity of an atom.
• Valence electrons- The electrons present in the valence shell i.e., the outermost shell of an atom are known as valence electrons.
• Valence electrons take part in the chemical reaction.
• These electrons decide the chemical properties of an atom.
• Sodium atom has 1 electron in its outermost shell which takes part in chemical bonding.
• Hence, The valency of sodium is 1.

3. Different energy shells, valence shell and valence electrons is shown in the following diagram.

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