In what way is the Rutherford’s atomic model different from that of Thomson’s atomic model?
Rutherford proposed that electron revolves around the nucleus in well-differentiated orbits. The nucleus is the centre which is positively charged. Rutherford proposed that the nucleus is very small and nearly all the mass of an atom is centred in the nucleus.
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Thompson proposed that electron are scattered positively charged spheres like a Christmas pudding and the mass of the atom was supposed to be uniformly distributed
Enlist the conclusions drawn by Rutherford from his alpha-ray scattering experiment.
Rutherford drawn following conclusion from his a-ray scattering experiment.
The ratio of the radii of hydrogen atom and its nucleus is 105. Assuming the atom and the nucleus to be spherical,
(i) What will be the ratio of their sizes?
(ii) If atom is represented by planet earth ‘Re ’ = 6.4 ×106 m, estimate the size of the nucleus.
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Why do Helium, Neon and Argon have a zero valency?
Helium has 2 electrons in its outermost orbit thus filling shell 1 and forming duplet configuration in the valence shell. Neon has 8 electrons in their valence orbit hence completing duplet configuration. In the same way, Argon and Neon have 8 electrons in its outermost shelling completing octet configuration. As these elements have a maximum electron in their valence shell thus reach stable electron configuration and they will not take part in any sort of chemical reactions
An element X has a mass number 4 and atomic number 2. Write the valency of this element?
Mass number = 4
Atomic number = 2
X is Helium.
It has 0 valency and it will not react with any other atom because it has its outer shell filled.
Fill in the blanks in the following statements
(a) Rutherford’s alpha-particle scattering experiment led to the discovery of the ———
(b) Isotopes have same ———but different———.
(c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be———and———respectively.
(d) The electronic configuration of silicon is ———and that of sulphur is ———
a) Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus
b) Isotopes have same atomic number but different mass number
c) Neon and chlorine have atomic numbers 10 and 17 respectively. Their valencies will be 0 and 1 respectively.
d) The electronic configuration of silicon is 2.8.4 and that of sulphur is 2.8.6
Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain
Helium has 2 electrons in its outermost shell thereby completing duplet configuration. Hence it has no valence shell left empty making its valency 0.
The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?
Elements with different atomic numbers but same mass numbers are known as isobars. Calcium and argon are isobars.
Match the names of the Scientists given in column A with their contributions towards the understanding of the atomic structure as given in column B
(A) – (B)
(a) Ernest Rutherford – (i) Indivisibility of atoms
(b) J.J.Thomson – (ii) Stationary orbits
(c) Dalton – (iii) Concept of the nucleus
(d) Neils Bohr – (iv) Discovery of electrons
(e) James Chadwick -(v) Atomic number
(f) E. Goldstein – (vi) Neutron
(g) Mosley – (vii) Canal rays
(A) – (B)
(a) Ernest Rutherford – (iii) Concept of the nucleus
(b) J.J.Thomson – (iv) Discovery of electrons
(c) Dalton – (i) Indivisibility of atoms
(d) Neils Bohr – (ii) Stationary orbits
(e) James Chadwick – (vi) Neutron
(f) E. Goldstein – (vii) Canal rays
(g) Mosley – (v) Atomic number
Calculate the number of neutrons present in the nucleus of an element X which is represented as 31X15
Mass number = No. of protons + No. of neutrons = 31
Number of neutrons = 31– number of protons
= 31–15
= 16
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