Q35 of 43 Page 30

An element X has a mass number 4 and atomic number 2. Write the valency of this element?

Atomic number of this element is 2. Its electronic configuration is K-2. The maximum number of electrons K shell can accommodate is 2. It means that its duplet is complete. It does not have to gain or lose any electron since, its outermost shell is complete with 2 electrons. Hence, the valency of this element is zero.


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33

Helium atom has 2 electrons in its valence shell but its valency is not 2, Explain.

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Fill in the blanks in the following statements

(a) Rutherford’s α-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 _____

 36

Why do Helium, Neon and Argon have a zero valency?

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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 ×10 m, estimate the size of the nucleus.