Question

Guys i need answers really fast plz help me
1. Describe Bohr’s model of atom
2. If the atomic number of Chlorine atom is 17 and atomic mass is 35.5u, compute the
number of protons, electrons and neutrons.
3. Define atomic number.
4. Define mass number.
5. Calculate the number of neutrons present in the nucleus of an element X which is
represented as 31 15 X.
6. The atomic number of fluorine is 9 and its mass number is 19. What is the number of
neutrons present in its nucleus?
7. Name the particles which determine the mass of an atom.
8. If an atom contains one electron and one proton, will it carry any charge or not? Justify.
9. Write the atomic number, mass number, number of protons, electrons and neutrons for
the first five elements.
10. How did Bohr’s model of atom explain the stability of an atom?

Grade 9 cbse

Answer 1

bohr's atomic model:

1) Bohrs atomic model states that the atom consists of a central body called nucleus where there are both neutrons (neutral charge or zero charge) and protons(positive charge) .

Therefore the overall charge in the nucleus is positive and the electrons(negative charge) revolve around the nucleus. These electrons revolve in orbitual path.. the orbits or energy level, also called shells hold them in place therefore the electrons are not attracted towards the centre and the stability is retained.

2) He has given a formula to calculate the no. of electrons in a particular shell which is

$2 {n}^{2}$

where n= 1 , 2, 3,4 for k, l, m, n shells respectively.

for k shell, n=1,therefore no of electrons = 2(1)²= 2

for l shell, n=2 therefore no of electrons = 2(2)²=8

for n shell, n=3 therefore no of electrons=2(3)²=18

for m shell,n=4 therefore no of electrons =2(4)²=32

3) electrons can jump from one energy level to another . if the electron moves to a higher energy level, then they are said to be at excited state,but if they stay at the same energy level or come back to the same energy level, then they are in/comimg back to ground state.