NCERT Questions

Class 9
Chapter 4 Class 9 - Structure of Atom

## Complete the following table.

 Atomic Number Mass Number Number of Neutrons Number of Protons Number of Electrons Name of the Atomic Species 9 - 10 - - - 16 32 - - - Sulphur - 24 - 12 - - - 2 - 1 - - - 1 0 1 0 -

Following are the formulae used while computing the table:

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

= Mass number - Atomic number

• First row:
i) Atomic number = 9 ,
Therefore, the number of protons = number of electrons = 9
ii) Mass number = Number of protons + Number of neutrons = 9 + 10 = 19.
(iii) The atomic species having atomic number 9 is Fluorine.

• Second row:
i) Atomic number = 16 ,
Therefore, the number of protons = number of electrons = 16
ii) Mass number - Number of protons = Number of neutrons
= 32 - 16 = 16

• Third row:
i) Number of protons = 12
Therefore, Number of protons = Number of electrons = Atomic number = 12
so the atomic number is 12 and the number of electrons is also 12.
ii) Mass number - Number of protons = Number of neutrons
= 24 - 12 = 12.
iii) The atomic species of atomic number 12 is Magnesium.

• Fourth row:
i) Number of protons = 1 ,
So, Number of protons = Number of electrons = Atomic number = 1
ii) Mass number - Number of protons = Number of neutrons
= 2 -1 = 1.

iii) The atomic species of atomic number 1 and mass number 2 is heavy Hydrogen or Deuterium.

• Fifth row:
i) Number of protons = 1 ,
So, Number of protons = Atomic number = 1

ii) The atomic species of atomic number 1 and mass number 1 is ordinary Hydrogen.
But since Number of electrons = 0, it is Hydrogen ion H+.

Now, we can complete the table using the above calculations: -

 Atomic Number (Z=p and e) Mass Number (A = p+n) Number of Neutrons (n) Number of Protons (p) Number of Electrons  (e) Name of the Atomic Species 9 9+10 = 19 10 9 9 Fluorine 16 32 32-16= 16 16 16 Sulphur 12 24 24-12= 12 12 12 Magnesium 1 2 2-1= 1 1 1 Deuterium 1 1 0 1 0 Hydrogen ion

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