STRUCTURE OF ATOM Flashcards
questions
give any two characteristic properties of cathode rays.
(i) They are negatively charged particles.
(ii) They can produce x–rays
Write any two characteristic properties of canal rays (anode rays).
: (i) They are positively charged particles.
(ii) Their properties depend on the nature of gas present in the cathode ray tube.
What are the important observations and conclusions made by Rutherford in his α–
particle scattering experiment ?
: The important observations are:
i. Most of the α– particles passed through the gold foil without any deviation.
ii. A small fraction of the α–particles was deflected by small angles.
iii. A very few α– particles were rebounded (Or, deflected by nearly 180°).
Conclusions:
i. Since most of the α–particles passed through the foil without any deviation, most
space in the atom is empty.
ii. In an atom, there is a positively charged centre called nucleus.
iii. The volume of the nucleus is negligibly small as compared to the total volume of the
atom.
What are the postulates of Rutherford atom model (Planetary model of atom)?
The important postulates are:
i. All the positive charge and most of the mass of the atom are concentrated at the centre
called nucleus.
ii. Electrons are revolving round the nucleus with a very high speed in circular paths called
orbits.
iii. Electrons and the nucleus are held together by electrostatic forces of attraction.
What are the drawbacks of Rutherford atom model?
: (i) He could not explain the stability of the atom.
(ii) He could not explain the electronic structure of atom
What is photoelectric effect?
: It is the phenomenon of ejection of electrons by certain metals (like potassium,
rubidium, caesium etc.) when light of suitable frequency incident on them. The electrons
ejected are called photoelectrons.
What are the important characteristics of photoelectric effect? [Write the important
results observed during photoelectric effect].
The important characteristics of photoelectric effect are:
i. The electrons are ejected from the metal surface as soon as the beam of light strikes the
surface.
ii. The number of electrons ejected is proportional to the intensity or brightness of light.
iii. For each metal, there is a minimum frequency (known as threshold frequency [ν0])
below which photoelectric effect is not observed.
iv. The kinetic energy of the ejected electrons is directly proportional to the frequency of
the incident light.
Give the different series of lines present in the line spectrum of hydrogen atom.
: The hydrogen spectrum consists of mainly five series of lines which are Lyman,
Balmer, Paschen, Brackett and Pfund series.
Series Spectral region
Lyman Ultra violet
Balmer Visible
Paschen Infra red
Brackett Infra red
Pfund Infra red
The series of lines in hydrogen spectrum that is visible to our naked eye is …………
Balmer series
Give the important postulates of Bohr Atom model.
i. The electron in the hydrogen atom can move around the nucleus in a circular path of
fixed radius and energy. These paths are called orbits or stationary states or allowed
energy states.
ii. The energy of an electron in the orbit does not change with time.
iii. The frequency of radiation absorbed or emitted when transition occurs between two
stationary states that differ in energy by ΔE, is given by:
ν = ΔE/h = (E2 – E1)/h
iv.The angular momentum of an electron is an integral multiple of h/2π.
Write any 3 limitations of Bohr atom model?
: (i) It could not explain the fine spectrum of hydrogen atom.
(ii) It could not explain the spectrum of atoms other than hydrogen.
(iii) It could not explain Stark effect and Zeeman effect.
What do you mean by the dual nature of matter?
: Matter has two types of nature – particle nature and wave nature. This is known as the dual nature of matter.
. Give the de Broglies equation and explain the terms?
: de Broglies equation is λ = h/p
Or, λ = h/mv , Where
λ is the wavelength,
m is the mass,
v is the velocity
p is the momentum of the particle
What will be the wavelength of a ball of mass 0.1 kg moving with a velocity of 10 m/s ? (h =6.626 x 10–34 Js)
Here m = 0.1 kg and v = 10 m/s
From the de Broglie’s equation, λ = h
mv
= (6.626 x 10^–34)/(0.1 x 10) = 6.626 x 10^–34 m
State Heisenberg’s uncertainty principle. Give its mathematical form
It states that “it is impossible to determine simultaneously, the exact position and
exact momentum (or velocity) of an electron”.
Mathematically,
Δx. Δp ≥ h/4π
OR, Δx. mΔv ≥ h/4π
Where Δx is the uncertainty in position, Δp is the uncertainty in momentum, Δv is the
uncertainty in velocity and m is the mass of electron.
