Q51 of 52 Page 45

Which group of elements could be placed in Mendeleev's Periodic Table without disturbing the original order? Give reason.

Noble gases could be placed in Mendeleev's Periodic Table without disturbing the original order.


According to Mendeleev’s classification, the properties of elements are the periodic function of their atomic masses and there is a periodic recurrence of elements with similar physical and chemical properties.


Noble gases were discovered much later after Mendeleev Periodic Table was discovered. Noble gases were placed in a separate group called Zero Group, after the 8th group. The placement of noble gases did not disturb the arrangement of any elements in the Mendeleev’s Periodic Table. Noble gases are present in very low concentration in the atmosphere and are chemically almost unreactive.


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48

(a) Electropositive nature of the element(s) increases down the group and decreases across the period.

(b) Electronegativity of the element decreases down the group and increases across the period.


(c) Atomic size increases down the group and decreases across a period (left to right)


(d) Metallic character increases down the group and decreases across a period.


On the basis of the above trends of the Periodic Table, answer the following about the elements with atomic numbers 3 to 9.


(a) Name the most electropositive element among them.


(b) Name the most electronegative element.


(c) Name the element with smallest atomic size.


(d) Name the element which is a metalloid.


(e) Name the element which shows maximum valency.

 49

An element X which is a yellow solid at room temperature shows catenation and allotropy. X forms two oxides which are also formed during the thermal decomposition of ferrous sulphate crystals and are the major air pollutants.

(a) Identify the element X.


(b) Write the electronic configuration of X.


(c) Write the balanced chemical equation for the thermal decomposition of ferrous sulphate crystals?


(d) What would be the nature (acidic/ basic) of oxides formed?


(e) Locate the position of the element in the Modern Periodic Table.

 50

An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell.

(a) Identify the element X. How many valence electrons does it have?


(b) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?


(c) Draw the electron dot structure for ammonia and what type of bond is formed in it?

 52

Give an account of the process adopted by Mendeleev for the classification of elements. How did he arrive at “Periodic Law”?