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Chap 5 : Periodic Classification of Elements www.cbse.online
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CBSE Previous Years Chapterwise Questions Exam 2019-2020 CHAPTER CHAPTER 55
CLASS : 10th
SUB : Science
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Periodic Classifi cation of Elements
ONE MARK QUESTIONS A(12): 2, 8, 2, B(18): 2, 8,8, C(20): 2, 8, 8, 2
A and C belong to the same group because they have
same number of valence electrons.
1. An element has atomic number 17. To which group 9. Why are H, Li, Na and K placed in group-1?
and period does it belong to? Ans : [CBSE 2015]
Ans : [CBSE 2016]
X(17): 2,8,7 is the electronic configuration. It has 7 It is because they have one valence electron.
valence electrons. It belongs to 17th group and 3rd 10. Write the number of horizontal rows in the modern
period. periodic table. What are these rows called?
2. Out of Li and K, which will have stronger metallic Ans : [CBSE 2014]
character and why? There are 7 horizontal rows in the modern periodic
Table. These rows are called periods.
Ans : [CBSE 2016]
K will have more metallic character because it can NO NEED TO PURCHASE ANY BOOKS
lose electrons easily due to its bigger atomic size and For session 2019-2020 free pdf will be available at
less effective nuclear charge. www.cbse.online for
3. Find the atomic number of the element whose 1. Previous 15 Years Exams Chapter-wise Question
electronic configuration is 2, 8, 5. Bank
2. Previous Ten Years Exam Paper (Paper-wise).
Ans : [CBSE 2016)
3. 20 Model Paper (All Solved).
Atomic number = 2 + 8 + 5 = 15. 4. NCERT Solutions
4. An element A has atomic number 16. To which group All material will be solved and free pdf. It will be
and period does it belong to? provided by 30 September and will be updated regularly.
Disclaimer : www.cbse.online is not affiliated to Central Board of Secondary Education,
New Delhi in any manner. www.cbse.online is a private organization which provide free
Ans : [CBSE 2016]
study material pdfs to students. At www.cbse.online CBSE stands for Canny Books
For School Education
A(16) has electronic configuration: 2, 8, 6. It has 6
valence electrons and three shells. It belong to Group
16, 3rd period. 11. Write one difference between Group 1 and Group 2
5. Write two reasons responsible for the late discovery of elements?
noble gases. Ans : [CBSE 2014]
Group 1 elements has 1 valence electron whereas
Ans : [CBSE 2015]
group 2 elements has 2 valence electrons.
a. They are inert i.e., least reactive.
b. They are less abundant in nature except Argon. 12. Write the atomic numbers of two elements X and Y
6. How many vertical columns are there in the modern having electronic configurations 2, 8, 2 and 2, 8, 6,
respectively.
periodic table and what are they called? Ans : [CBSE 2014]
Ans : [CBSE 2015, 2014] X = 2 + 8 + 2 = 12
There are 18 vertical columns in Modern Periodic Y = 2 + 8 + 6 = 16
Table. They are called groups.
7. List any two properties of elements belonging to the 13. State the modern periodic law of classification of
elements.
first group of modem periodic table. Ans : [CBSE 2014, 2013]
Ans : [CBSE 2015, 2014] Modern Periodic Law: It states ‘properties of elements
a. They have 1 valence electron. are a periodic function of their atomic number’.
b. Their valency is equal to 1.
8. The atomic number of three elements A, B and C are 14. Out of the three elements P, Q and R having atomic
numbers 11, 17 and 19 respectively, which two elements
12, 18 and 20 respectively. State giving reason, which will show similar properties and why?
two elements will show similar properties. Ans : [CBSE 2014]
Ans : [CBSE 2015, 2014] P(11): 2, 8, 1; Q(17): 2, 8, 7; R(19): 2, 8, 8, 1
Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 53
Chap 5 : Periodic Classification of Elements www.cbse.online
P and R will show similar chemical properties because after the formation of Mendeleev’s periodic table.
they have the same number of valence electrons. Ans : [CBSE 2011]
15. Write the formula which is used to determine the Gallium and Germanium.
maximum number of electrons that a shell can 25. What is a metalloid? Name any two of them.
accommodate.
Ans : [CBSE 2014, 2013] Ans : [CBSE 2011]
2n2, where n is the shell number. Metalloids are those elements which resembles both
with metals as well as non-metals e.g., Boron and
16. What would be the nature of oxides formed by the Silicon.
elements on the right side of periodic table? 26. Arrange the following metals in decreasing order of
Ans : [CBSE 2014]
their atomic size:
On right hand side of the periodic table, most of them Ca, Mg, Ba, Be
are non-metals, therefore they form acidic oxides. Ans : [CBSE 2011]
17. Predict the maximum number of valence electrons Ba > Ca > Mg > Be is the decreasing order of atomic
possible for atoms in the first period of the periodic size.
table. 27. Why does atomic size decreases as we move from left
Ans : [CBSE 2014}
to right along a period in a periodic table?
Maximum number of valence electrons in 1st period Ans : [CBSE 2011]
is 2. It is because one proton and one electron is being
18. The electronic configuration of two elements X and Y added successively, therefore effective nuclear charge
are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the atomic increases, atomic size decreases.
numbers of X and Y. 28. What is the valency of silicon with atomic number 14?
Ans : [CBSE 2013]
Ans : [CBSE 2010]
X = 2 + 8 + 7 = 17 Si(2, 8, 4), the number of valence electrons in Si is 4.
Y = 2 + 8 + 8 + 3 = 21 Therefore, its valency is 4.
19. The atomic numbers of three elements X, Y and Z are 29. What is the valency of phosphorus with atomic
3, 11 and 17 respectively. State giving reason which number 15?
two elements will show similar properties.
Ans : [CBSE 2010]
Ans : [CBSE 2013]
X= 2, 1 P(2, 8, 5) has 5 valence electrons, therefore its valency
Y = 2,8, 1; Z = 2, 8, 7 is equal to 3.
X and Y will show similar properties due to same 30. What is the valency of an element with atomic number
number of valence electrons. 35?
20. Give reason why noble gases are placed in a separate Ans : [CBSE 2010]
group in the modern periodic table. Atomic number is 35, it has electronic configuration
of 2, 8, 18, 7. It has 7 valence electrons, therefore its
Ans : [CBSE 2013]
It is because they have their outermost shell completely valency is equal to 1.
filled and resemble with each other. 31. What were the criteria used by Mendeleev in creating
21. Name any two pairs of elements which were adjusted his periodic table?
by Newlands in the same slot. Ans : [CBSE 2013]
Increasing order of atomic mass and same formula of
Ans : [CBSE 2013]
(i) Co and Ni, (ii) Ce and La oxides and hydrides.
22. Define Newlands law of octaves. 32. Give the number of elements in 2nd and 5th period in
the modern periodic table.
Ans : [CBSE 2013]
Ans : [CBSE 2013]
Newlands Law of Octaves: When elements are arranged In 2nd period, there are 8 elements.
in increasing order of their atomic mass, every eighth In 5th period, there are 18 elements.
element resembles with the first.
23. State Mendeleev’s periodic law. 33. Lithium, Sodium and potassium form a Dobereiner’s
Ans : [CBSE 2012] triad. The atomic masses of lithium and potassium
are 7 and 39 respectively. Predict the atomic mass of
Mendeleev’s Periodic Law: Properties of elements are sodium.
a periodic function of their atomic mass. Ans : [CBSE 2009C]
24. Name any two elements which were discovered later Atomic mass of Sodium
Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 54
Chap 5 : Periodic Classification of Elements www.cbse.online
Atomicmassof lithium Group 1 Group 2
+Atomicmassof potassium
= 2 Li(3): 2,1 Be(4): 2, 2
73 46 K(19):2,8,8,1 Mg (12): 2, 8, 2
+ 9
Na = =23
= 2 2
34. Why was the system of classification of elements into Li and K are placed in group 1 due to same number of
valence electrons. In second group the atomic number
triads not found suitable? of first two elements will be 4 and 12 respectively.
Ans : [CBSE 2009(C)]
It is because all the elements discovered at that time 40. Calcium is an element with atomic number 20.
could not be classified as Dobereneire’s triads. a. Will it be a metal/non-metal?
b. What will be its valency?
35. The formula of magnesium oxide is MgO. State the c. What would be the formula of its chloride?
formula of barium nitrate and barium sulphate, if d. Will it be smaller / larger than K?
barium belongs to same group as magnesium. Ans : [CBSE 2016]
Ans : [CBSE 2012]
Ca(20): 2, 8, 8, 2
The valency of Mg is 2. The valency of Ba is also 2 a. It will be a metal.
as they belong to the same group. Formula of Barium b. Its valency is equal to 2.
c. CaCl is the formula of its chloride.
nitrate is Ba(NO ) , and that of Barium sulphate is 2
BaSO. 3 2 d. It will be smaller than K.
4
36. Which has larger atomic radius, K(19) or Ca(20)? NO NEED TO PURCHASE ANY BOOKS
For session 2019-2020 free pdf will be available at
Ans : [CBSE 2016]
K has larger atomic radius than Ca. www.cbse.online for
1. Previous 15 Years Exams Chapter-wise Question
37. Chlorine, Bromine and Iodine form Dobereiner’s Bank
triads. The atomic mass of Cl and I are 35.5 and 126.9 2. Previous Ten Years Exam Paper (Paper-wise).
respectively. Predict the atomic mass of Bromine. 3. 20 Model Paper (All Solved).
4. NCERT Solutions
Ans : [CBSE 2009]
All material will be solved and free pdf. It will be
Atomic Mass of Br provided by 30 September and will be updated regularly.
Atomicmassof Cl+Atomicmassof I Disclaimer : www.cbse.online is not affiliated to Central Board of Secondary Education,
New Delhi in any manner. www.cbse.online is a private organization which provide free
= 2 study material pdfs to students. At www.cbse.online CBSE stands for Canny Books
For School Education
35..162.
5+1269 4
=81.2
= = 2
Electronic configuration: X = 287,, 41. List the anomalies of Mendeleev’s periodic table which
It has 7 valence electrons. It belongs to group 17. were removed in Modem Periodic Table.
It has 3 shells, therefore it belongs to 3rd period. Ans : [CBSE 2016]
It can gain 1 electron to become stable, so its valency Co with higher atomic mass proceeds Ni with lower
is equal to 1. atomic mass. It was solved because Co has lower
TWO MARKS QUESTIONS atomic number than Ni.
Isotopes should have been given different slots
due to different atomic mass, but it is not possible due
38. An element X has mass number 35 and the number of to same chemical properties. The problem was solved
its neutrons is 18. Identify the group number, period because isotopes have same atomic numbers.
and valency of element X’. 42. Choose from the following:
Ans : [CBSE Sample Paper 2017-2018, CBSE 2016] C, O, Ne, Na, S1
6 8 10 11 14
X has mass number 35, number of neutrons = 18 a. Elements that should be in the same period.
Atomic Number = 35 - 18 = 17 b. Elements that should be in the same group.
a. Electronic configuration: X = 2, 8, 7 It has 7 State the reason for your selection in each case.
valence electrons. It belongs to group 17. Ans : [CBSE 2016,2012]
b. It has 3 shells, therefore it belongs to 3rd period.
c. It can gain 1 electron to become stable, so its a. C(2, 4), O(2, 6), Ne(2, 8) belong to the same
6 8 10
valency is equal to 1. period i.e., 2nd period and Na(2, 8, 1), Si(2, 8,
11 14
39. Why is lithium with atomic number 3 and potassium 4) belongs to the same period i.e., 3rd period.
b. C(2,4) and Si(2,8,4) belongs to the same group
with atomic number 19 are placed in group one? What 6 14
-14 due to same number of valence electrons,
will be atomic number of the first two elements in the which is equal to 4.
second group?
43. The elements X, Y and Z having atomic numbers 11,
Ans : [CBSE 2016]
7 and 6 respectively react with oxygen to form their
Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 55
Chap 5 : Periodic Classification of Elements www.cbse.online
oxides. 49. An element ‘X’ has atomic number 13.
a. Arrange these oxides in increasing order of their a. Write its electronic configuration.
basic nature. b. State the group to which ‘X’ belongs to.
b. Give reason for your answer. c. Is ‘X’ a metal or a non-metal?
d. Write the formula of its bromide.
Ans : [CBSE 2015]
X(11) is sodium and it will form Na O, Y(7) is Ans : [CBSE 2012]
2
Nitrogen that will form N O , Z(6) is carbon which a. X(13) : 2, 8, 3
will form CO . 2 5 b. It belongs to group 13.
2
a. NO < CO < NaO c. It is a metal.
2 5 2 2
b. It is because non-metallic character increases d. XBr is the formula of its bromide.
along a period, therefore basic character of oxides 3
decreases, and acidic nature increases from left to 50. State the modern periodic law for the classification of
right across the period. elements. How many (a) groups, (b) periods are there
in Modern Periodic Table?
44. a. Name the element with atomic number 17. Ans : [CBSE 2012]
b. To which period does it belong to? Properties of elements are a periodic function of their
c. To which group does it belong to? atomic numbers. There are 18 groups and 7 periods in
d. Write its electronic configuration. modern periodic table.
Ans : [CBSE 2015,2014]
a. Chlorine (17): 2, 8, 7 51. An element M has atomic number 11.
b. It belongs to 3rd period. a. Write its electronic configuration.
c. It belongs to group 17. b. State the group to which M belongs to.
d. 2, 8, 7 is the electronic configuration of chlorine. c. Is M a metal or a non-metal?
d. Write the formula of its chloride.
45. a. Amongst the following elements identify the ones Ans : [CBSE 2012]
that would form anions: a. 2, 8, 1
K, O, Na, F, Ca, Cl, Mg b. M belongs to group 1.
b. Write the electronic configuration of the anions c. It is a metal.
identified above. d. MCI is the formula of its chloride.
Ans : [CBSE 2015, 2014]
O, F, Cl will form anions. 52. An element M has atomic number 12.
O2- (18): 2, 8 a. Write its electronic configuration.
-(10): 2, 8 b. State the group to which M belongs to.
F
Cl-(18): 2, 8, 8 c. Is M a metal or a non-metal?
d. Write the formula of its oxide.
46. An element belongs to third period and second group Ans : [CBSE 2012]
of the periodic table: a. 2, 8, 2,
a. State the number of valence electrons in it. b. Group 2,
b. Is it a metal or a non-metal? c. Metal,
c. Name the element. d. MO is formula of its oxide.
d. Write the formula of its oxide.
Ans : [CBSE 2015, 2011] 53. How can the valency of an element be determined if
a. It has 2 valence electrons. its electronic configuration is known? What will be
b. It is a metal valency of an element with atomic number 9?
c. Magnesium. Ans : [CBSE2012,2011]
d. MgO is the formula of its oxide. Valency=Number of valence electrons in case of
47. Write the trend of atomic size and metallic character metals and metalloids. It is also equal to 8 — Number
along a group and a period in modern periodic table. of valence electrons in case of non-metals.
Ans : [CBSE 2013, 2012] F(9) has electronic configuration of 2, 7. It is a non-
metal. Its valency is equal to 1.
Atomic size increases down the group and decreases 54. An element X belongs to 3rd period and group 17 of the
along a period from left to right in the periodic table.
Metallic character increases down the group and it periodic table. State its (a) electronic configuration,
decreases along a period from left to right. (b) valency. Justify your answer with a reason.
Ans : [CBSE2012]
48. Elements in Periodic table show periodicity in a. 2, 8, 7; because it has 3 shells as it belongs to
properties. List any four such properties. 3rd period. Group 17 means 7 valence electrons.
Ans : [CBSE2013] b. Valency = 1
Valence electrons, Valency, Atomic size, Metallic It can gain 1 electron to become stable i.e. to
character. complete its octet.
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