Q24 of 48 Page 1

The elements of the third period of the Periodic Table are given below:


(a) Which atom is bigger, Na or Mg? Why?


(b) Identify the most (i) metallic and (ii) non-metallic element in Period 3.


(c) Which is more non-metallic, S or Cl?


(d) Which has higher atomic mass, AI or Cl?

(a) Na is bigger than Mg. This is because on moving from left to right in a period, there is an increase in the no. of electrons due to increase in the atomic number. So. Na is bigger than Mg.


(b) (i) The most metallic element is Na and most non-metallic element is Cl in out of these elements. Most metallic element is Na. As we move from left to right, the nuclear charge on elements increased due to increase in the number of protons. With increase in the nuclear charge, the force with which the valence electrons are pulled becomes more stronger and becomes difficult for the atoms to lose the outermost electrons. Therefore, when we move from left to right in a period, the metallic character of the element decreases and non-metallic character increases.


(c) Cl is more non-metallic than S because on moving from left to right, with increase in the nuclear charge, the force with which the valence electrons are pulled becomes more stronger and becomes difficult for the atoms to lose the outermost electrons and thereby tendency to gain the electrons increases


(d) When we move from left to right in a period, the atomic number increases which results in increase in atomic mass and therefore, Cl has higher atomic mass than Al.


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A student takes 2 mL acetic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He makes the following observations:

I. A colourless and odourless gas evolves with a brisk effervescence.


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I. Sodium hydroxide is in the form of pellets.


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IV. The red litmus paper turns blue when dipped into the solution.


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