Page 103 - Chemistry ICSE Class IX

Atomic Structure and Chemical Bonding 91
Since the cathode rays get de ected towards the positively charged electrode, this shows that the particles
constituting cathode rays are negatively charged particles.
Q.3. Who determined the charge-to-mass ratio of the positive rays and how?
Ans. Wein determined the charge-to-mass ratio of the positive rays by using Thomson’s technique.
Q.4. What are the differences in the discharge tubes used to study cathode rays and positive rays?
Ans. The discharge tubes used to study cathode rays and positive rays differ as follows:
(a) The discharge tube used to study positive rays has two chambers, whereas the one used to study cathode
rays has only one chamber.
(b) The discharge tube used to study positive rays has a cathode having holes in it, whereas the one used to
study cathode rays has a solid cathode.
Q.5. Which problem of atomic structure was solved by the discovery of neutron?
Ans. Rutherford found that except for hydrogen, the atomic masses of the atoms could not be explained in terms of
only electrons and protons. To explain this, Rutherford predicted the presence of a neutral particle inside the
nucleus. This neutral particle was later discovered and named neutron. Thus, the discovery of neutron solved
the problem associated with the mass of the atom.
Q.6. Where do you think the electrons in the cathode rays come from?
Ans. Electrons in the cathode rays come from the cathode as well as from the gas present in the discharge tube.
Q.7. Which observation in Thomson’s discharge tube experiments showed that cathode rays could not be the rays of
light?
Ans. Bending (de ection) of the cathode rays by the electric and magnetic elds was taken as an evidence that cathode
rays consisted of a stream of particles and not a ray of light.
Q.8. Which observation led to the discovery of neutron?
Ans. The observation that the atomic masses of all elements (except hydrogen) are much higher than expected on the
basis of the presence of only electrons and protons led to the discovery of neutron.
Q.9. Name four things based on the principle of discharge tube.
Ans. The following things are designed on the basis of the principle of discharge through gases at very low pressures:
(a) Neon-sign advertising boards (b) Television tubes
(c) Fluorescent tubes (d) Sodium vapour lamps

ASSIGNMENT 1

Discharge through gases, Cathode rays, Anode rays, Electron, Proton, Neutron

ϭ͘ tŚŝĐŚ ŽďƐĞƌǀĂƟŽŶ ŝŶ ƚŚĞ ĚŝƐĐŚĂƌŐĞ ƚƵďĞ ĞdžƉĞƌŝŵĞŶƚ ŝŶĚŝĐĂƚĞƐ ƚŚĂƚ
;ĂͿ ĐĂƚŚŽĚĞ ƌĂLJƐ ĐŽŶƐŝƐƚ ŽĨ ŶĞŐĂƟǀĞůLJ ĐŚĂƌŐĞĚ ƉĂƌƟĐůĞƐ͍
;ďͿ ĐĂƚŚŽĚĞ ƌĂLJ ƉĂƌƟĐůĞƐ ƉŽƐƐĞƐƐ ŵŽŵĞŶƚƵŵ͍
;ĐͿ ĐĂƚŚŽĚĞ ƌĂLJƐ ƚƌĂǀĞů ŝŶ ƐƚƌĂŝŐŚƚ ůŝŶĞƐ͍
Ϯ͘ /Ŷ ĂŶ ĞdžƉĞƌŝŵĞŶƚ͕ Ă ĐĞƌƚĂŝŶ ƚLJƉĞ ŽĨ ƌĂĚŝĂƟŽŶ ŝƐ ƉƌŽĚƵĐĞĚ͘ dŚŝƐ ƌĂĚŝĂƟŽŶ
;ĂͿ ŐĞƚƐ ĚĞŇĞĐƚĞĚ ƚŽǁĂƌĚƐ ŶĞŐĂƟǀĞ ĞůĞĐƚƌŝĐĂů ĮĞůĚ
;ďͿ ĐĂŶ ƌŽƚĂƚĞ Ă ƉĂĚĚůĞ ǁŚĞĞů
;ĐͿ e/m ǀĂůƵĞ ŝƐ ůŽǁ ĂŶĚ ĚĞƉĞŶĚƐ ƵƉŽŶ ƚŚĞ ŶĂƚƵƌĞ ŽĨ ƚŚĞ ŐĂƐ ƚĂŬĞŶ ŝŶ ƚŚĞ ĚŝƐĐŚĂƌŐĞ ƚƵďĞ͘ EĂŵĞ ƚŚĞ ƌĂĚŝĂƟŽŶ͘
ϯ͘ ŽŵƉĂƌĞ ƚŚĞ ĐŚĂƌĂĐƚĞƌŝƐƟĐƐ ŽĨ ĂŶ ĞůĞĐƚƌŽŶ͕ Ă ƉƌŽƚŽŶ ĂŶĚ Ă ŶĞƵƚƌŽŶ͘
ϰ͘ EĂŵĞ ƚŚĞ ƐĐŝĞŶƟƐƚƐ ǁŚŽ ĚŝƐĐŽǀĞƌĞĚ
;ĂͿ ĞůĞĐƚƌŽŶ ;ďͿ ƉƌŽƚŽŶ ;ĐͿ ŶĞƵƚƌŽŶ

The Structure of Atom

After the discovery of electrons and protons, Sir J. J. Thomson proposed the
atomic model. This is described here in brief.