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How are you all
So Today in This post I'm going to give you Periodic classification of elements For class 10th ,11th,12th
.
Believe me if you solve this fully then you can clear your exam very well.
periodic classification of elements
1 An element has 12 protons. The group and period to which this element belongs to is
(a) 2nd group, 3rd period
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(b) 2nd group, 2nd period
(c) 3rd group, 2nd period
(d) 3rd group, 3rd period
ANS: (a)
2 Which of the following is correct order of atomic size?
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(a) Cl < F < Br < I (b) F < Cl < Br < I
(c) I < Br < Cl < F (d) Br < I < Cl < F
ANS: (b)
3 In Mendeléev’s Periodic Table, gaps were left for the elements to be discovered later. Which of the following elements found a place in the periodic table later ?
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(a) Germanium (b) Chlorine
(c) Oxygen (d) Silicon
ANS: (a)
4 Where would you locate the element with electronic configuration 2, 8 in the Modern Periodic Table ? 1
(a) Group 8 (b) Group 2
(c) Group 18 (d) Group 10
ANS: (c)
5 On going down in a group of the periodic table, the size of atoms _________. 1 ANS: increases
6 Those elements which have the same valence shell, belongs to the same _________ of the periodic table. 1 ANS: period
7 When an element from the left side of the periodic table combines with an elements from the right side of the periodic table, _________ bond is formed. 1
ANS: ionic
8 There are 7 groups and 18 periods in a modern periodic table. [True/False] 1 ANS: False
9 How did Dobereiner classify the elements? 1 ANS: He classified elements in group of three, such that atomic weight of middle element is average of 1st and 3rd element.
10 Give one example of such triads. 1 ANS: Li(7), Na(23), K(39)
11 Chlorine, bromine and iodine form a Dobereiner’s triad. The atomic masses of chlorine and iodine are 35.5 and 126.9 respectively. Predict the atomic mass of bromine. 1
ANS: Atomic mass of Br
12 Out of the three elements P, Q and R having atomic numbers 11, 17 and 19 respectively, which two elements will show similar 1
properties and why?
ANS: P(11): 2,8,1 R(19): 2, 8, 8, 1 Q(17): 2, 8, 7
Elements P, R will show similar properties as they belong to they same group with valency 1 due to same number of valance electrons.
13 The atomic numbers of three elements X, Y and Z are 3, 11 and 17 respectively. State giving reason which two elements will show similar chemical properties. 1
ANS: X and Y will show similar chemical properties as these have same valence electrons. 14 Out of Li and K, which have stronger metallic character and why? 1 ANS: K because it has larger size and more tendency to lose electron.
Calcium is an element with atomic number 20. Stating the reason answer each of the following questions:
(i) Is calcium a metal or non-metal?
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(ii) Will its atomic radius be larger or smaller than that of potassium with atomic number 19?
(iii) Write the formula of its oxide.
ANS: (i) Ca (20): 2, 8, 8, 2
It is metal because it can lose 2 electrons to become stable.
(ii) It will be smaller due to greater effective nuclear charge.
(iii) CaO is formula of its oxide
16 An element ‘X’ is placed in the 3rd group and 3rd period of the Modern Periodic Table. Answer the following questions stating reason for your answer in each case:
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(a) Write the electronic configuration of the element ‘X’.
(b) Write the formula of the compound formed when the element ‘X’ reacts with another element ‘Y’ of atomic number 17.
(c) Will the oxide of this element be acidic or basic?
ANS: (a) ‘X’ has electronic configuration 2, 8, 3.
(b) ‘X’ has valency equal to 3. ‘Y’ has electronic configuration 2, 8, 7, so valency = 1.
is formula of compound formed.
(c) Oxide of this element will be basic.
17 Study the following table in which positions of six elements A, B, C, D, E and F are shown as they are in the Modern Periodic
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Table: On the basis of the above table, answer the following questions:
(i) Name the element which will form only covalent compounds.
(ii) Which element is a metal with valency one?
(iii) Which element is a non-metal with valency two?
(iv) Out of D and E, which has a bigger atomic radius and why?
(v) Write the formula of the compound formed when B combines with D.
ANS: (i) Element E will form covalent compounds only by sharing its four valence electrons.
(ii) Element D is a metal with valency one.
(iii) Element B is a non-metal with valency two.
(iv) Moving left to right across a period, atomic radius decreases due to increase in effective nuclear charge, so element D will have bigger atomic radius.
(v) Electronic configuration of B = 2, 6; valency of B = 2
Electronic configuration of D = 2, 8, 1; valency of D = 1
Molecular formula of the compound formed with B and D So, the formula of the compound formed when elements B and D combine is BD2.
18 Write the number of periods the modern periodic table has. How do the valency and metallic character of elements vary on moving from left to right in a period? How do the valency and atomic size of elements vary down a group? 3
ANS: The periodic table has 7 periods in periodic table.
Valency first increases from left to right till the middle then decreases in a period.
Metallic character decreases along a period from left to right.
Atomic size goes on increasing down the group, whereas valency remains the same in a group.
19 The elements Li, Na and K, each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.
(a) In which group of the periodic table should they be?
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(b) Which one of them is least reactive?
(c) Which one of them has the largest atomic radius? Give reason to justify your answer in each case.
ANS: (a) Group 1 as these have one valence electron.
(b) Li is least reactive due to smallest size, highest effective nuclear charge and less tendency to lose electron. (c) K is largest in size as it has four shells.
20 The electronic configuration of an element ‘X’ is 2, 8, 8, 2. To which (a) period and (b) group of the modern periodic table does
‘X’ belong? State its valency. Justify your answer in each case. 3
ANS: (a) It belongs to fourth period as it has four shell.
(b) It belong to 2nd group as it has 2 valence electrons.
(c) Its valency is equal to 2 because it can lose 2 electrons to become stable.
21 The element Be, Mg, Ca are placed in the second group of the periodic table. Their atomic numbers are 4, 12, 20 respectively. 3
(a) Write the electronic configuration of these elements.
(b) Write the valency exhibited by them.
(c) Which of the three elements will be most reactive?
ANS: (b) Valency = 2
(c) Ca is most reactive because it is largest in size due to least effective nuclear charge It can lose electron easily.
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