Atoms

Question 1

graph of scattering angle with no. of α particles scattered

Answer 1

kind of like inversely proportional

Question 2

Significance of α particle experiment

Answer 2

Most of them passed undeflected
Most space of atom is empty
Few deflected through 90 & 180
All +ve charge & the mass of atom is concentrated in a very small region called nucleus
Size of nucleus is 1/10^15m & that of atom is 1/10^10m
Since gold nucleus is much heavier than α particle, gold nucleus remains at rest

Question 3

Impact parameter

Answer 3

Perpendicular distance of initial velocity vector of α particle from center of nucleus

Question 4

For large impact parameter, α particle is

Answer 4

almost undeflected

Question 5

For head on collision, impact parameter is

Answer 5

0

Question 6

Rutherford’s postulates

Answer 6

Entire +ve charge & mass of atom is concentrated at very small volume at the center called nucleus
Amount of +ve charge is equal to -ve charge
Atom is neutral
E’s are continuously revolving around the nucleus in circular orbits
Force of attraction provides necessary centripetal force

Question 7

Limitations of Rutherford’s atomic model

Answer 7

1. an accelerating particle emits radiation as EM waves. So energy of the electron show gradually decrease leading to decrease in radius of e’ orbit
2. Electron follows a spiral path & finally fall into the nucleus so atom isn’t stable
3. As e’ spiral inwards, their angular velocity & their freq change continuously they would emit continuous spectrum instead of actually observed line spectrum

Question 8

Bohr’s atomic model

Answer 8

1. In a H atom, an e’ revolves in stable orbits called stationary orbits
2. These orbits are those for which angular momentum is integral multiple of h/2pi
   As long as e’ is revolving in stationary orbit, it doesn’t radiate energy. When e’ make a transition from higher energy to lower, a photon is emitted, having energy equal to energy diff b/n initial & final states

Question 9

radius of orbit r =

Answer 9

n²h²ε/Ze²pi m

Question 10

Are stationary orbits equally spaced?

Answer 10

No

Question 11

Speed _______ as we move away from the nucleus

Answer 11

decreases

Question 12

Potential energy U =

Answer 12

-kZe²/r

Question 13

Kinetic energy K =

Answer 13

kZe²/2r

Question 14

E =

Answer 14

-mZ²e⁴/8ε²n²h²

Question 15

-ve sign in E indicates that?

Answer 15

e’ is bound to nucleus so energy is needed to be done to separate e’ from nucleus

Question 16

Rydberg const

Answer 16

1.1 x 10⁷ per metre

Question 17

For lyman series, n2 =

Answer 17

2,3,4,….

Question 18

Lyman series lies in

Answer 18

UV region

Question 19

Balmer region lies in

Answer 19

1st 4 lines in visible region and later in UV

Question 20

For alpha H, n1 & n2 =

Answer 20

2; 3

Question 21

For beta H, n1 & n2 =

Answer 21

2; 4

Question 22

Paschen and Pfund lies in

Answer 22

IR region

Question 23

Excitation energy of atom

Answer 23

Energy required by an e’ to jump from the ground state to any one of excited states

Question 24

Ionisation energy

Answer 24

Energy required to knock an e’ completely out of atom

Question 25

Limitations of Bohr’s model

Answer 25

1. Capable only to H like atoms
2. Couldn’t explain fine structure of spectral lines
3. Doesn’t explain why only circular orbits are chosen where elliptical orbits are possible
4. Doesn’t tell anything about relative intensities of various spectral lines
5. Fails to explain further splitting of spectral lines in M.F & E.F

Question 26

Zeeman effect

Answer 26

Splitting of spectral lines in M.F

Question 27

Stark effect

Answer 27

Splitting of spectral lines in E.F

Question 28

Alpha particle has _________ penetrating power

Answer 28

least

Question 29

Lyman in ___ range

Answer 29

UV

Question 30

Balmer in ____ range

Answer 30

visible

Question 31

Paschen, Brackett, Pfund in ___ range

Answer 31

Infra Red