The elements Li, Na, and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.

i. To which group of the modern periodic table these elements belong?

ii. Which one of them is least reactive?

iii. Which one of them has the largest atomic radius?

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Solution

i. The given elements belong to Group 1 of the modern periodic table as all of them have one valence electron.
ii. Li is least reactive because its outermost orbit is very near to the nucleus. So the removal of electron is difficult.

iii. K has the largest atomic radius because it has more number of shells as compared to Na and Li.

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(b) Why do elements in the same group show similar properties but the elements in different groups show different properties?
(c) For each of the following triads, name the element with the characteristics specified below:

Elements	Least atomic radius	Chemically least reactive
(i) F, Cl, Br (ii) Li, Na, K	.................... ....................	.................... ....................

(d) State one reason for keeping fluorine and chlorine in the same group of the periodic table.
(e) What are the merits of the modern periodic table of elements?

Q. (a) What were the two major shortcomings of Mendeleev's periodic table? How have these been removed in the modern periodic table?
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(c) To which groups of the modern periodic table do the elements X and Y belong? Give reason for your answer.
(d) What could the elements X and Y be? Write their names and symbols.

Question 4
Which of the following statement(s) about the Modern Periodic Table are incorrect?

(i) The elements in the Modern Periodic Table are arranged on the basis of their decreasing atomic number

(ii) The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic masses

(iii) Isotopes are placed in adjoining group (s) in the Periodic Table

(iv)The elements in the Modern Periodic Table are arranged on the basis of their increasing atomic number

(a) (i) only
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) (iv) only

Na, Mg, and Al are the elements of the 3rd period of the Modern Periodic Table having group numbers 1, 2, and 3 respectively. Which one of these elements has the highest valency (b) largest atomic radius and (c) maximum chemical reactivity? Justify your answer stating the reason for each.

Q. Be, Mg and Ca are the elements of the 2nd group of the Modern Periodic Table having same valency and belongs to period 2, 3 and 4 respectively. Which one of these elements has the a) highest metallic nature b) least atomic radius c) maximum chemical reactivity. Justify the answer stating the reason for each.

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The elements Li, Na, and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table. i. To which group of the modern periodic table these elements belong? ii. Which one of them is least reactive? iii. Which one of them has the largest atomic radius?

The elements Li, Na, and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.

i. To which group of the modern periodic table these elements belong?

ii. Which one of them is least reactive?

iii. Which one of them has the largest atomic radius?