Question

Long Answer Type Questions:-

Q 107] Answer in brief.

a)What is pauli's exclusion principle? on basis of pauli's principle show that the maximum number of electrons in the M-shell (n=3) of any individual atom is 18. ( 2 Mark)

b)Write a short note on Aufbau principle. ( 1 mark)



c)Explain Rutherford nuclear model of atom (Gold foil experiment) ( 2 marker)

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Answer 1

1] ραυℓi's єxcℓυsiσท ρriทciρℓє :-

" No two electrons in an atom can have the same set of four quantum numbers".

according to pauli's exclusion principle, "only two electrons may exits in the same orbital and these electrons must have opposite spin."

➜For M-shell n=3,

➜Maximum number of electrons in the shell = $\mathrm{2n^{2}}$

$\implies\mathrm{2(3)^{2}}$

$\implies\mathrm{2(9)}$

$\implies\mathrm{18}$

Therefore, the maximum number of electrons in the M-shell of any individual atom is 18.

2] αυՔвαυ ρriทciρℓє :-

" In the ground state of the atoms, the subshells are filled in the order of their increasing energies."

➜In case, two or more subshells have same energy then electron can be filled in those subshell, which has least 'n' value.

3] Rυτнєrfσr∂ ทυcℓєαr мσ∂єℓ σf ατσм:-

ıηтяσ∂υcтıση:-

Rutherford and his students bombarded very thin gold foil with alpha particles. The source of the alpha particles was radium, a radioactive substances, placed in a block of lead. slits were used to get a fine beam. the presence of alpha particles at any point around the thin foil of gold after striking it was detected with the help of a circular zinc sulphide screen. The point at which an alpha particle strikes this screen, a flash of light is given out.

σвsєrvατiσทs:-

• Most of the alpha particles passed through the foil without undergoing any deflection.

• Few alpha particles underwent deflection thought small angels.

• very few( only one in 20,000) were bounced back. i.e were deflected by nearly 180°.

cσทcℓυsiσทs:-

• The fact that the majority of the particles went though the foil undetected shows that most of the space in an atom is empty.

• The scattering of a particles through smaller angles and very few though longer angles suggest that protons are not distributed in an atom, instead they're all grouped at the center.

• The heavy positively charged central part is called as nucleus.

• Nearly all the mass of the atom is concentrated in the nucleus.

∂iαgrαм:-

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Answer 2

$\huge \mathcal{ \fcolorbox{cyan}{black}{ \pink{αиѕωєя}}}$

α) According to Pauli's exclusion principle, "only two electrons may exist in the same orbital and these electrons must have opposite spin."

For M-shell n = 3

Maximum number of electrons in the shell

= 2n2 = 2(3)2 = 18

в) The Aufbau principle states that electrons fill lower-energy atomic orbitals before filling higher-energy ones (Aufbau is German for "building-up"). By following this rule, we can predict the electron configurations for atoms or ions.

¢) The gold-foil experiment showed that the atom consists of a small, massive, positively charged nucleus with the negatively charged electrons being at a great distance from the centre. Niels Bohr built upon Rutherford's model to make his own.

• fσя αиѕωєя ¢ иσтє тнє αвσνє αттα¢нмєит тσσ!!