Structure Of Atom Flashcards

Question

Explanation of Photoelectric Effect

Answer 1

(i) Photoelectrons are ejected only when the incident light has a certain minimum frequency (threshold frequency v0) (ii) If the frequency of the incident light (v) is more than the threshold frequency (v0), the excess energy (hv – hv0) is imparted to the electron as kinetic energy. (iii) On increasing the intensity of light, more electrons are ejected but the energies of the electrons are not altered.

Answer 2

When a ray of white light passing through a prism splits up into seven different wide bands of colours from violet to red (like rainbow). These colours are so continuous that each of them merges into the next.

Answer 3

When vapours of some volatile substance fall on flame of a Bunsen burner and analysed with spectroscope. Some specific coloured lines appear on the photographic plate which are different for different substances.

Answer 4

When white light is passed through the vapours of a substance and the transmitted light is then allowed to strike a prism, dark lines appear in the continuous spectrum. It indicates that the radiations were absorbed by the substance from white light. Dark lines appear exactly at the same positions where the lines in the emission spectra appear.

Answer 5

When electric discharge is passed through hydrogen gas enclosed in discharge tube under low pressure and the emitted light is analysed by a spectroscope, the spectrum consists of a large number of lines which are grouped into different series known as hydrogen spectrum. v' = 109,677(1/n1^2 - 1/n2^2)/cm RH = Rydberg constant for hydrogen and n2 > n1 For Lyman series, n1= 1, n2= 2, 3, 4, 5……….. For Balmer series, n1 = 2, n2 = 3, 4, 5, 6……….. For Paschen series, n1= 3, n2 = 4, 5, 6, 7……….. For Brackett series,n1 = 4, n2 = 5, 6, 7, 8……….. For Pjund series, n1 =5, n2 = 6, 7, 8, 9………..

Answer 6

1/lambda = v' = R x Z^2(1/n1^2 - 1/n2^2)

Answer 7

In an atom, the electrons revolve around the nucleus in certain definite circular paths called orbits. (ii) Each orbit is associated with definite energy and therefore these are known as energy levels or energy shells. These are numbered as 1, 2, 3... or K, L, M, N.. (iii) Only those energy orbits are permitted for the electron in which angular momentum of the electron is a whole number multiple of (h/2π) (iv) As long as electron is present in a particular orbit, it neither absorbs nor loses energy (v) When energy is supplied to an electron, it absorbs energy only in fixed amounts and jumps to higher energy state away from the nucleus known as excited state. The excited state is unstable, the electron may jump back to the lower energy state and in doing so, it emits the same amount of energy.

Answer 8

1. Explained the stability of an atom. 2. Helped in calculating energy of electron

Answer 9

(i) could not explain atomic spectra of multielectron atoms. (ii) failed to explain splitting of spectral lines in presence of magentic/electric field. (iii) failed to explain the ability of atoms to form molecule formed by chemical bonds (iv) failed to explain 3D model of atom and shapes

Answer 10

lambda = h/mc

Answer 11

It is impossible to determine simultaneously, the exact position and exact momentum (or velocity) of an e' delta V . delta x = (h/4pi)m

Answer 12

6.626 x 10^-34 Js

Answer 13

Infra red lines

Answer 14

visible line

Answer 15

-2.18 x 10^-18/n^2 J/atom

Answer 16

r(n)=a(0).n^2 where a(0)=52.9pm

Answer 17

V=V(o)/n V= V(o)/n .Z V(o)=2.188x10^8 cm/s