In Online Education Chapter 5 Periodic Classification of Elements Class 10 Science Important Questions and Answers PDF will help you in scoring more marks. This consists of 1 mark Questions, 3 Mark Numericals Questions, 5 Marks Numerical Questions and previous year questions from Chemical Reactions and Equations Chapter.

Online Education for Periodic Classification of Elements Class 10 Important Questions and Answers Science Chapter 5

Very Short Answer Questions

Question 1.
Indicate the elements which belong to the same group from their atomic numbers as 9, 17, 24, 30, 35, 45.
Answer:
Elements with atomic numbers 9, 17 and 35 belong to the same group i.e. halogen family.

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Question 2.
Arrange the following in decreasing atomic size :
(i) Na, Mg, K
(ii) N, F, O
(iii) N, S, P
Answer:
(i) K, Na, Mg
(ii) N, O, F
(iii) P, S, N.

Question 3.
Give the name and electronic configuration of second alkali metal.
Answer:
The second alkali metal is sodium (Na). Its electronic configuration is 2, 8, 1.

Question 4.
What is the similarity in the electronic configuration of Mg, Ca and Sr ?
Answer:
All the elements belong to group 2 and have two electrons in their valence shell.

Question 5.
Name the members of alkaline earth family. Which out of them is radioactive in nature ?
Answer:
The members of alkaline earth family (group 2) are : Be, Mg, Ca, Sr, Ba, Ra. The last element radium (Ra) is radioactive in nature.

Question 6.
The two isotopes of chlorine have atomic mass 35 u and 37 u. Should they be placed in separate slots in the periodic table ?
Answer:
No, they should be placed in the same slot (or position) because the periodic table is based on the atomic numbers of the elements. Both the isotopes of the element chlorine have the same atomic number (Z = 17).

Question 7.
An element “X” has mass number 35 and number of neutrons is 18.
Identify group number and period of the element “X”.
Answer:
Atomic number of X = Mass No. – No. of neutrons = 35 – 17 = 18.
Electronic configuration = 2, 8, 7;
Group No. = 17, Period No. = 3.

Question 8.
Flow does metallic character of the elements vary
(i) in a group
(ii) in a period ?
Answer:
(i) The metallic character of the elements increases downwards in a group.
(ii) The metallic character of the elements decreases from left to the right along a period.

Question 9.
Name three elements which behave as metalloids.
Answer:
The elements are : arsenic (As), antimony (Sb) and germanium (Ge).

Question 10.
Which property do all the elements possess which are present in the same period as the element boron ?
Answer:
In all the elements, the last electron is present in the same shell i.e., L-shell or second shell.

Question 11.
Which common property do all the elements present in the same group have as the element fluorine ?
Answer:
All the elements have the same number of electrons (seven) in their valence shells.

Question 12.
Write the electronic configuration of the element present in the third period and seventeenth group of the periodic table.
Answer:
The group 17 consists of halogens. The halogen present in third period is chlorine (Cl) with atomic number (Z) = 17.

Question 13.
What is the basic difference in the electronic configuration of the elements belonging to group 1 and group 2 ?
Answer:
All elements belonging to group 1 have one electron in the valence shell while all elements belonging to group 2 have two electrons in their valence shell.

Question 14.
Three elements X, Y and Z belong to 17th group but to 2nd, 3rd and 4th period respectively. Number of valence electrons in Y is 7. Find the number of valence electrons in X and Z.
Answer:
All the elements present in a group have same number of valence electrons whatever may the periods to which they belong. Since element Y has 7 valence electrons, the elements X and Z have also 7 valence electrons.

Question 15.
Element ‘Y’ with atomic number 3 combines with element A’ with atomic number 17. What would be the formula of the compound ?
Answer:
The electronic distribution in elements A’ and ‘Y’ are 2, 1 and 2, 8, 7 respectively. Both have valency equal to 1. The formula of the compound is AY.

Question 16.
Name two other elements which belong to the same family as.
(i) fluorine
(ii) calcium
(iii) carbon.
Answer:
(i) chlorine, bromine
(ii) magnesium, strontium
(iii) silicon, germanium.

Question 17.
On the basis of the periodic classification, identify each set belonging to either a group or a period :
(a) Na, Mg, Al
(b) Na, K, Rb
(c) B, C, N
(d) He, Ne, Ar.
Answer:
(a) period
(b) group
(c) period
(d) group.

Question 18.
The formula of magnesium oxide is MgO. Write the formula of magnesium chloride.
Answer:
Oxygen is divalent in nature. The valency of magnesium in magnesium oxide is +2. The formula of magnesium chloride is MgCl2 since chlorine has valency equal to one.

Question 19.
The electronic configuration of an element is 2, 8, 7. What is its expected valency ?
Answer:
The expected valency of the element is 1. It may be calculated as 8 – 7 = 1

Question 20.
Two elements A and B belong to the same period. What is common in them ?
Answer:
They have the same number of shells.

Question 21.
The electronic configuration of an element is 2, 8, 6. Identify the element and name of the family to which it belongs.
Answer:
The element with configuration 2, 8, 6 (Z= 16) is sulphur. It belongs to oxygen family (group 16).

Question 22.
How would tendency to gain electrons change as you go down a group ?
Answer:
It is expected to decrease since atomic size increases down the group and the tendency of the element to gain electrons decreases.

Question 23.
Why do elements present in a group show similar characteristics after definite gaps of atomic numbers 8, 8, 18, 18, 18, 32 ?
Answer:
This is because of the reason that the same valence shell configuration of the atoms gets repeated after definite gaps of atomic numbers.

Short Answer Questions

Question 24.
Identify the non-metals from the elements given below.
(a) 2, 8, 1
(b) 2, 8, 7
(c) 2, 8, 3
(d) 2, 8, 5.
Answer:
The element chlorine (Cl) corresponding to configuration (b) and the element phosphorus (P) corresponding to configuration (d) are both non-metals.

Question 25.
Identify the elements X and Y from the following information.
(a) X has 17 protons and 18 neutrons
(b) Y has 17 protons and 20 neutrons.
Answer:
Both the elements X and Y are the isotopes of the same element chlorine because they have the same number oi protons (17).
Remember : Two different elements cannot have the same number of protons. Therefore, X and Y are the isotopes of the same element.

Question 26.
Identify the elements from the following characteristics and arrange them in increasing order of metallic character.
(a) An element which imparts golden yellow colour to the flame.
(b) An element whose oxide is used as a white wash.
(c) An element which is constituent of chlorophyll i.e. green colouring matter in plants.
Answer:
(a) Sodium
(b) Calcium
(c) Magnesium.
Sodium (Na) belongs to group 1. Both calcium (Ca) and magnesium (Mg) are present in group 2. The element Ca is placed below Mg in the group. Since the metallic character of the elements decreases along a period and increases down the group, in the light of these observations, the increasing order of metallic character is : Mg < Na < Ca.

Question 27.
(a) Atomic numbers of Mg and Al are 12 and 13 respectively. “Write their electronic configuration.
(b) Mention the period of the Modern Periodic Table to which the above two elements belong. Give reason for your answer.
Answer:
(a) The electronic configuration of the elements are
Mg(Z = 12) 2, 8, 2 ;
Al (Z = 13) 2, 8, 3.
(b) Both these elements belong to third period since their atoms have three shells.

Question 28.
From the part of a periodic table, answer the following questions

1
Hydrogen

 2 13 14
Carbon		 15 16
Oxygen

17
Fluorine

X

 P Q

Y

R
Z

T

(a) Atomic number of oxygen is 8. What would be the atomic number of, Fluorine ?
(b) Out of ‘X’ and ‘Q’ which element has larger atomic size ? Give reason for your answer.
(c) Out of ‘Y’ and ‘Z’ which element has smaller atomic size ? Give reason for your answer.
Answer:
(a) Atomic number of Fluorine is (8 + 1) = 9.
(b) Since the atomic size of the elements decreases along a period the element ‘Q’ has a smaller size than element ‘X’.
(c) Since the atomic size of the elements increases down the group, the element ‘Y’ has a smaller size than element ‘Z’.

Question 29.
Calcium is an element with atomic number 20.
(i) Is it a metal or non-metal ?
(ii) Will its size be more or smaller than that of potassium?
(iii) Write the formula of its chloride.
Answer:
The electronic configuration of calcium (Z = 20) is 2, 8, 8, 2.
(i) Since it has only two valence electrons, it is present in group 2. It is a metal.
(ii) Both potassium (K) and calcium (Ca) are present in fourth period. Since atomic size decreases along a period, calcium is smaller in size.
(iii) The valency of calcium is 2. The formula of its chloride is CaCl2.

Question 30.
An element ‘X’ has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’.
Answer:
Atomic number of the element ‘X’ = 35 – 18 = 17
Electronic configuration of the element ‘X’ = 2, 8, 7
Group number = 17;
Period number = 3.
Valency of the element ‘X’ = 8 – 7 = 1.

Question 31.
Given below are some of the elements of first group Li, Na, K
(Their atomic numbers are 3, 11, 19 respectively and they belong to 2nd, 3rd and 4th period respectively). Arrange these in the decreasing order of metallic character exhibited by them.
Answer:
All the three elements belong to the group (1) of alkali metals. Since the metallic character of the elements increases down a group, the decreasing order of metallic character is K > Na > Li.

Question 32.
Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the modern periodic table do these two elements belong ? What type of bond will be formed between them and why ?
Answer:
Electronic configuration : X (Z = 12); 2, 8, 2 Electronic configuration : Y (Z = 16); 2, 8, 6
Both these elements are present in third period since they have three electron shells.
These are likely to form an ionic bond as a result of transference of two electrons from element X to the element Y. The compound will form compound XY.

Question 33.
An element has electronic configuration 2, 8, 3. What is the atomic number of the element ? To which
(i) group and
(ii) period does this element belong ?
Answer:
(i) Atomic number of the element (Z) = 2 + 8 + 3= 13
(ii) Group to which the element belongs =13

Question 34.
(a) What is common in the elements belonging to the same period in the periodic table ?
(b) Why are chlorine and bromine kept in the same group in the periodic table ?
Answer:
(a) The elements belonging to the same period have same number of shells. For example, the elements placed in the second period have two shells (K, L). Similarly, the elements included in the third period have three shells (K, L, M). ‘
(b) Both the elements have same number of valence electrons (7) in their atoms.
Chlorine (Z = 17) 2, 8, 7;
Bromine (Z = 35) 2, 8, 18, 7
That is why these are placed in the same group in the periodic table.

Question 35.
An element belongs to third period and second group in the periodic table.
(a) State number of valence electrons in it.
(b) Is it a metal or non-metal ?
(c) Name the element
(d) Write the formula of its oxide
Answer:
The element belonging to third period and second group is calcium (Z = 20). Its electronic configuration is 2, 8, 8, 2
(a) It has two valence electrons
(b) The element is a metal
(c) The element is calcium (Ca)
(d) The formula of calcium oxide is CaO.

Question 36.
(a) The elements of the second period along with their atomic numbers in parentheses are given below ;
B (5), Be (4), O(8), N(7), Li (3), C (6), F (9)

  1. Arrange them in the same order as they appear in the periodic table.
  2. Which element has the largest and smallest atom ?

(b) Why does atomic radius change as we move from left to right in a period ?
Answer:
(a)

  1. Li (3), Be (4), B (5), C (6), N (7), O(8), F (9)
  2. The element Li has the largest atom. The element F has the smallest atom.

(b) Along a period, the nucleus charge increases and the electrons are attracted more towards the nucleus.
Therefore, the atomic size or atomic radius decreases as we move from left to the right along a period.

Question 37.
Account for the following :
(a) Elements C, N, O and F are placed in the second period of the periodic table. .
(b) Elements of group 17 are monovalent.
Answer:
(a) All these elements have two electron shells. Therefore, these are placed in the second period.
C (Z=6) 2, 4 ;
N (Z = 7) 2, 5 ;
O (Z = 8) 2, 6 ;
F (Z = 9) 2, 7
(b) All the elements included in the group 17 have 7 valence electrons in their atoms. These atoms need only one electron to acquire the electronic configuration of nearest noble gas atom. Therefore, these are monovalent.

Question 38.
Chlorine (atomic number 17) is more electronegative than sulphur (atomic number 16). Explain.
Answer:
Chlorine (Z = 17) is placed after sulphur (Z = 16) in the same period i.e. third period. The size of chlorine is smaller than that of sulphur and its atom needs only one electron to have noble gas electronic configuration while sulphur atom needs two electrons. Therefore, chlorine has greater attraction for electrons than sulphur. It is more electronegative than sulphur.

Question 39.
The atomic numbers of three elements X, Y and Z are 9, 11 and 17 respectively. Which of these two elements will show similar characteristics and why ?
Answer:
The elements X and Z will show similar characteristics because they differ in their atomic numbers by 8 (9, 17). Both these are halogens and belong to group 17 (halogen family). These are fluorine (Z= 9) and chlorine (Z = 17) .

Question 40.
The atomic number of three elements are given below :

Element (symbol)

 A B C
Atomic number 5 7

10

Write the symbol of the element which belongs to
(i) group 13,
(ii) group 15, of the periodic table. State the period of the periodic table to which these elements belong. Give reason for your answer.
Answer:
Electronic configuration of the elements A, B and C are as given :

Element (Symbol)

 A B C
Atomic number 5 (2, 3) 7 (2, 5)

10(2, 8)

Element (Symbol) A B C
Atomic number 5 (2, 3) 7 (2, 5) 10(2, 8)
(i) Element A belongs to group 13 (Group No. = 10 + 3 = 13). It is boron (B)
(ii) Element B belongs to group 15 (Group No. = 10 + 5 = 15). It is nitrogen (N)
Both these elements belong to second period since they have two shells.

Question 41.
Write two reasons responsible for the late discovery of noble gases.
Answer:
(i) Noble gas elements were not present in earth crust as minerals like other elements and were present in air to a very small extent.
(ii) Their atoms have stable electronic configuration of their outermost shells also called valence shells. (2 in case of He and 8 for other elements). They do not combine with atoms of other elements.
That is why noble gas elements were discovered at a later stage.

Long Answer Questions

Question 42.
Three elements A, B and C have atomic numbers 7, 8 and 9 respectively.
(a) What would be their positions in the modern periodic table ? (Mention group and period both)
(b) Arrange A, B and C in decreasing order of their size.
(c) Which one of the three elements is most reactive and why ?
Answer:
The electronic configuration of these elements are :
(a) A ( Z = 7) 2, 5;
B (Z = 8) 2, 6;
C (Z = 9) 2, 7
Position of element A = 15th group and 2nd period
Position of element B = 16th group and 2nd period ‘
Position of element C = 17th group and 2nd period.
(b) In general, atomic size decreases along a period. Therefore, decreasing order of size is A > B > C
(c) The element C (Z = 9) is fluorine. It is the most reactive element since it needs only one electron to acquire a noble gas configuration.

Question 43.
The elements with atomic number 3 to 10 belong to the second period. Taking into account the trends in the general periodic properties, predict.
(a) The most electronegative element
(b) The most electropositive element
(c) The element belonging to noble gas family
(d) The element which constitutes large number of organic compounds.
Answer:
(a) The most electronegative element has atomic number (Z) = 9. It is fluorine (F).
(b) The most electropositive element has atomic number (Z) = 3. It is lithium (Li)
(c) The element belonging to noble gas family has atomic number (Z) = 10. It is neon (Ne)
(d) The element which constitutes large number of organic compounds has atomic number (Z) = 6. It is carbon (C).

Question 44.
“Elements in Periodic Table show periodicity of properties”. List any four properties.
Answer:
Periodicity i.e., repetition of similar properties is shown by the elements present in a group and separated by definite gaps of atomic number. For example,

  1. Elements in a group have same number of valence electrons and same valency.
  2. Elements present in a group show similar chemical properties.
  3. The atomic sizes of the elements in a group increase regularly.
  4. The m.p. and b.p. of the elements in a group increase regularly.

Question 45.
The electronic configuration of three elements X, Y and Z are given below ;
X = 2 ; Y = 2, 6 ; Z = 2, 8, 2.

  1. Which element belongs to the second period ?
  2. Which element belongs to the eighteenth group ?
  3. Which element belongs to the second group ?
  4. What is the valency of Y ?
  5. Are Y and Z metals or non-metals ?

Answer:

  1. The element ‘Y’ belongs to second period.
  2. The element ‘X’ belongs to eighteenth group also called zero group.
  3. The element ‘Z’ belongs to second group.
  4. Element ‘Y’ has valency equal to 2(8 -6 = 2).
  5. The element ‘Y’ is a non-metal while element ‘Z’ is a metal.

Question 46.
The atomic numbers of elements A, B, C, D and E are given below :

Element

 A B C D E
Atomic no. 7 10 12 4

19

From the above table, answer the following questions
(a) Which two elements are chemically similar ?
(b) Which is an inert gas ?
(c) Which element belongs to 3rd period of periodic table ?
(d) Which element among these is a non-metal ?
Answer:
The electronic configuration of the elements are as follows :

Element

 A B C D

E

Atomic no.

7(2, 5)

 10 (2, 8) 12 (2, 8, 2) 4 (2, 2) 19 (2, 8, 8, 1)

(a) Elements C and D are chemically similar since they have same number of valence electrons.
(b) Element B is an inert gas element since it has complete octet.
(c) Element C belongs to third period since it has three shells.
(d) Element A is a non-metal since it has five valence electrons.

Question 47.
Using the part of the periodic table given below, answer the questions that follow.

Group ⇒ Period⇓

 I II III IV V VI VII

Zero

1

 H He

2

 Li Be B c N o F Ne
3 Na Mg Al Si P s Cl

Ar
4 K Ca

(i) Na has physical properties similar to which elements and why ?
(ii) Write the electronic configuration of N and P.
(iii) State one property common to fluorine and chlorine.
Answer:
(i) Na has physical properties similar to Li and K. All the three elements have one electron each in the valence shell of their atoms. These are known as alkali metals. However, the element hydrogen has different physical properties.
(ii) Electronic configuration of N (Z = 7) = 2, 5
Electronic configuration of P (Z = 15) = 2, 8, 5
(iii) Both the elements have seven electrons in the valence shells as their atoms and have valency equal to one.
Fluorine (Z = 19) 2, 7 ;
Chlorine (Z = 17) 2, 8, 7.

Question 48.
Atomic radii of the elements present in second period are given :
Periodic Classification of Elements Class 10 Important Questions and Answers Science Chapter 5 image - 1

  1. Arrange them in decreasing order of their atomic radii.
  2. Are these elements arranged in the pattern of a period in the periodic table ?
  3. Which elements have the largest and the smallest atoms ?
  4. How does the atomic radius change as you move from left to right in a period ?

Answer:

  1. The decreasing order of atomic radii is :
    Li(152) > Be (111) > B (88) > C(77) > N(74) > O(66)
  2. No, the arrangement of the elements is not systematic. The correct arrangement is as given above.
  3. The element Li has the largest atoms while the element O has the smallest atoms.
  4. The atomic radii of the elements decrease in moving from left to the right.

Question 49.
“The atomic number of Cl is 17. On the basis of this information, answer the questions that follow :
(a) Write the electronic configuration of Cl.
(b) Find its valency.
(c) To which group does it belong ?
(d) Identify the type of ion it will form.
(e) Write down the formula of the compound it forms with other elements.
Answer:
(a) Electronic configuration of Cl (Z = 17) = 2, 8, 7.
(b) Valency of Cl = 8 – 7 = 1
(c) Group to which Cl belongs =17 id) Type of ion formed bly Cl = Anion (Cl–).
(e) Formula of compound with other elements (M) = MCIx.
∴ Here x is the valency of the element.

Question 50.
The list of the elements present in the same period but in different groups is given :
1           2            13            14               15             16           17             18
(a) Do these groups represent modern periodic table ?
(b) Which element will belong to oxygen family ?
(c) Which element will not take part in chemical combination ?
(d) The elements belonging to which groups will form ionic bonds most readily ?
Answer:
(a) Yes, these groups of elements represent modern periodic table.
(b) The element present in group 16 belongs to oxygen family.
(c) The element included in group 18 (noble gas elements) will not take part in chemical combination.
(d) The elements belonging to group 1 and group 17 will form ionic bonds most readily.

Question 51.
An element E has following electronic configuration :
Periodic Classification of Elements Class 10 Important Questions and Answers Science Chapter 5 image - 2
(a) To which group of the periodic table does element E belong ?
(b) To which period of the periodic table does element E belong ?
(c) State the number of valence electrons present in element E.
(d) State the valency of the element E.
Answer:
The element with atomic no. (Z) = 16 is sulphur (S).
(a) It belongs to group 16 of the periodic table,
(b) It belongs to third period since it has three shells.
(c) The element has six valence electrons.
(d) The valency of the element is 2 (8 – 6 = 2).

Question 52.
From the part of the periodic table given, answer the following questions.

1
Lithium

 2 13 14
Carbon		 15 16
Oxygen		 17
L

18
Neon

X

 S P Q

Y

R

Z

 T

(a) Which is the most reactive metal ?
(b) Name the family of L, Q, R, T.
(c) Name one element of group 2 and 15,
(d) Name one member of group 18 other than neon.
(e) Give the name of the element S placed below carbon in group 14.
Answer:
(a) The element Z is the most reactive metal.
(b) The elements are present in group 17. The family is that of halogens.
(c) One element belonging to group 2 is calcium (Ca) while one present in to group 15 is nitrogen (N).
(d) The element argon (Ar) is also present in group 18.
(e) The element is silicon (Si)

 

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