Question

atomic number of an a element 12 and mass number is 25.find the number of electrons,protons, neutrons and electronic configuration of the atmo.draw the bhor structure of the atom .class9​

Answer 1

1. The number of electrons is 12.

2. The number of protons is 12.

3. The number of neutron is 13.

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How to find number of electrons ?

➞ We know that the number of electrons is equal to the number of protons.

How to find number of neutrons ?

➞ We can find number of neutrons by subtracting the Mass number from Number of protons.

Example :-

If the mass number is 4 u and the number of protons is 2. Find the number of neutrons.

➞ Number of neutrons = Mass number - Number of protons.

➞ Number of neutrons = 4 - 2

➞ Number of neutrons = 2

So,the number of neutrons is 2.

Points to remember :-

• Number of electrons = Number of protons.

• Mass number = Number of neutrons + Number of protons.

• Atomic number = Number of protons.

Answer 2

Z = 12 (Atomic number)

A = 25 (Mass number)

We know,

Z = No. of protons

A = No. of nucleons

$\therefore$ p ${}^{+}$ = 12 = e ${}^{-}$

n = 25 - 12 = 13

Electronic configuration: 2 + 8 + 2 [follow 2n², where 'n' = energy level index].

N.B.:-

Attachment 1: Atomic structure of the above element.

Attachment 2: Bohr's model of an atom.