# Class 10 Science Chapter 5 Periodic Classification of Elements

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### Class 10 Science Chapter 5 Periodic Classification of  Elements

Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 5 Periodic Classification of Elements Solutions for All Subjects, You can practice these here…

Q.1. ( a ) On what basis did Mendeleev arrange the elements in his periodic table ?

( b ) On which basis are they arranged now ?

Ans :- ( a ) Atomic masses.

( b ) Atomic numbers .

Q.2. State whether the following statements are true or false :

( a ) Newlands divided the elements into horizontal rows of eight elements each .

( b ) According to Mendelev’s periodic law , the proporties of elements are a periodic function of their atomic numbers .

( c ) The elements in a group have consecutive atomic numbers .

Ans :- ( a ) False.

( b ) False.

( c ) False.

Q.3. Name the scientist who said that the proporties of elements are a periodic functions of their atomic masses.

Ans :- Mendeleev.

Q.4. Name the scientists who gave the following laws in the early classification of elements :

( a ) Law of octaves.

( b ) Law of triads.

Ans :- ( a ) Newlands

( b ) Dobereiner.

Q.5. Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table .

Ans :- Gallium , Scandium .

Q.6. Which group of elements could be placed in Mendeleev’s periodic table later on , without disturbing the original order ? Give reason .

Ans :- Noble gas. They are chemically unreactive .

Q.7. ( a ) What is the number of valence electrons in the atoms of first element in a period ?

( b ) What is the usual number of valence electrons in the atoms of the last element in a period ?

Ans :- ( a ) 1

( b ) 8

Q.8. State whether the following statement is true or false : on going down in a group of the periodic table , the number of valence electrons increases .

Ans :- False .

Q.9. Name the element which is in :

( a ) first group and third period.

( b ) seventeenth group and second period .

Ans :- ( a ) Sodium.

( b ) Fluorine.

Q.10. Arrange the following elements in increasing order of their atomic radii Li , Be , F , N

Ans :- F < N < Be Li

Q.11. Arrange the following elements in the increasing order of their metallic character :

Mg , Ca , k , Ga

Ans :- Ga < Mg < Ca < K

Q.12. Rewrite the following statements after correction , if necessary :

( i ) Elements in the same period have equal valency.

( ii ) The metallic character of elements in a period increases gradually on moving from left to right.

Ans :- Elements in the same group have equal valency.

( ii ) The metallic character of elements in a period decreases gradually on moving from left to right .

Q.13. Define periods nand groups.

Ans :-  A periodic table consists of horizontal rows of elements called periods and vertical column called groups .

Q.14. The three elements predicted by Mendellev from the gaps in his periodic table were known as eka – boron, eka – aluminium and eka – silicon . What names were given to these elements when they were discovered later on ?

Ans :- Scandium , Gallium , Germanium .

Q.15. X and Y are the two elements having similar properties which obey Newlands ‘ law of octaves . How many elements are there in – between X and Y ?

Ans :- Six elements .

Q.16. Fill in the blanks :

( a ) The basis for modern periodic table is ———.

( b ) Group 1 elements are called ————-.

( c ) Group 18 elements are called ————-.

( d ) The horizontal rows in a periodic table are called————–.

( e ) On moving from right to left in the second period the number of valence electrons ————–.

( f ) The tendency to gain an electron ———— on moving down in a group of the periodic table.

Ans :- ( a ) Atomic number.

( b ) Alkali metals.

( c ) Noble gases .

( d ) Periods.

( e ) Decreases.

Q.1. The elements X , Y and Z belong to groups 2 , 14 and 16 respectively , of the periodic table .

( a ) Which two elements will form covalent bond ?

( b ) Which two elements will form an ionic bond ?

Ans :- Let us write down the above given data more clearly as follows :

Group 2                Group 14               Group 16

X                              Y                             Z

( a ) We know that a covalent bond is formed between two non metal elements . Now , out of elements X , Y and Z the element Y and element Z are non – metals . Thus , the elements Y and Z will form covalent bonds .

( b ) An ionic bond is formed between a metal and a non- metal . Now , out of the above given elements , the elements X is a metal and elements Z in non – metal . Thus the elements X and Z will form an ionic bond .

Q.2. The electronic configuration of an element X is :

K                     L                      M

2                     8                       6

( i ) What is the group number of element X in the periodic on table ?

( ii ) What is the period number of element X in the periodic table ?

( iii ) What is the number of valence electrons in an atom of X ?

( iv ) What is the valency of X ?

( v ) Is it a metal or a non – metal ?

Ans :- ( i ) From the above given electronic configuration we find the element X has 6 valence electrons . So the group number of element X in the periodic table is 6 + 10 = 16

( ii ) Element X has 3 electron shells in its atom , so the period number of X is 3. That is X belongs to 3rd period of the periodic table .

( iii ) Element X has 6 valence electrons .

( iv ) Element X has 6 valence electrons so it needs 2 more electrons to complete its octet and become stable. Thus the valency of element X is 2 .

( v ) The elements of group 16 are non – metals . So , X is a non – metal .

Q.3. ( a ) On which side of the periodic table will you find metals ?

( b ) On which side of the periodic table will you find non metals ?

( c ) What is the name of those elements which divide metals and non – metals in the periodic table ?

Ans :- ( a ) Left side.

( b ) Right side.

( c ) Metalloids.

Q.4. ( a ) Name three elements that have a single electron in their outermost shells .

( b ) Name two elements that have two electrons in their Shouter most shells .

( c ) Name three elements with completely filled outermost shells .

Ans :- ( a ) Lithium , sodium , Potassium .

( b ) Magnesium , Calcium.

( c ) Helium , Neon , m Argon .

Q.5 . Nitrogen ( atomic number 7 ) and phosphorus ( atomic number 15 ) belong to group 15 of the periodic table . Write the electronic configuration of these two elements . Which of these will be more electronegative ? Why ?

Ans :- Electronic configuration of Nitrogen = 2, 5

Electronic configuration of phosphorous = 2, 8, 5

Nitrogen will be more electronegative because its atom has small size due to which the attraction of its nucleus for the incoming electron is more .

Q.6. An elements X belongs to group 2 and another element Y belongs to group 15 of the periodic table :

( a ) What is the number of valence electrons in X ?

( b ) What is the valency of X ?

( c ) What is the number of valence electrons for Y ?

( d ) What is the valency of Y ?

Ans :- ( a ) 2

( b ) 2

( c ) 5

( d ) 3

Q.7. ( a ) What is the usual number of valency electrons and valency of group 18 elements of the periodic table ?

( b ) What happens to the number of valence electrons in the atoms of elements as we go down in a group of the periodic table ?

Ans :- ( a ) Usual number of valence electrons is 8. The valency of group 18 elements of the periodic table is zero .

( b ) The number of valence electrons remains the same.

Q.8. The atomic numbers of the three elements X , Y and Z are 2 , 6 and 10 respectively .

( i ) Which two elements belong to the same group ?

( ii ) Which two elements belong to the same period ?

Ans :- ( i ) X and Z

( ii ) Y and Z

Q.9. An atom has the electron structure of 2 , 7 .

( a ) What is the atomic number of this atom ?

( b ) To , which of the following would it be chemically similar ? 7ᴺ , 15ᴾ, 17ᶜⁱ , 18ᴬʳ

( c ) Why would you expect it to be similar ?

Ans :- ( a ) 9

( b ) 17ᶜⁱ

( c ) Both have the same number of electrons in their atoms .

Q.10. In each of the following pairs , choose the atom having the bigger size ?

( a ) Mg ( at no . 12 ) or Cl ( at no . 17 )

( b ) Na ( at no . 11 ) or K ( at no . 19 )

Ans :- ( a ) Cl

( b ) K

Q.11. The atomic numbers of three elements A , B and C are given below :

( i ) Which element belongs to group 18 ?

( ii ) Which element belongs to group 15 ?

( iii ) Which element belongs to group 13 ?

( iv ) To which period / periods do these elements belong?

Ans :- ( i )  C

( ii )  B

( iii ) A

( iv ) 2nd period.

Q.12. An element Y is in second period and group 16 of the periodic table :

( i ) Is it a metal or non – metal ?

( ii ) What is the number of valence electrons in its atom ?

( iii ) What is its valency ?

( iv ) What is the name of the element ?

( v ) What will be the formula of the compound formed by Y with sodium ?

Ans :- ( i ) Non metal

( ii ) 6

( iii ) 2

( iv ) Oxygen

( v ) Na₂ Y

Q.13. Atoms of eight elements A , B , C , D , E , F , G and H have the same number of electron shells but different number of electrons in their outermost shells . It was found that elements A and G combine to form an ionic compound . This ionic compound is added in a small amount to almost all vegetables and dishes during cooking . Oxides of elements A and B are basic in nature while those of elements E and F are acidic . The oxide of element D is , however , almost neutral . Based on the above information , answer the following questions :

( a ) To which group of period of the periodic table do these elements belong ?

( b ) What would be the nature of compound formed by a combination of elements B and F ?

( c ) Which two of these elements could definitely be metals ?

( d ) Which one of the eight elements is most likely to be found in gaseous state at room temperature ?

( e ) If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively , write the formula of the compound formed by the combination of C and G.

Ans :- ( a ) 3rd period

( b ) Ionic compound

( c ) A and B

( d ) H

( e ) CG₃

Q.14. A non metal X which is the largest constituent of air combines with hydrogen when heated in the presence of iron as catalyst to form a gas Y. When gas Y is treated with sulphuric acid , it forms a compound Z which is used as a chemical fertilizers .

( a ) What are X , Y and Z ?

( b ) To which group of periodic table does X belong ?

( c ) Name the period of periodic table in which X is placed .

( d ) Which element is placed just before X in the period?

( e ) Which element is placed just after X in the period ?

Ans :- ( a ) X is nitrogen gas , N₂

Z is ammonia gas NH₃

Z is ammonium sulphate ( NH₄ )₂ SO₄

( b ) 15th group.

( c ) 2nd period.

( d ) carbon.

( e ) oxygen.

Q.15. The atomic masses of three elements X , Y and Z having similar chemical properties are 7, 23 and 39 respectively .

( a ) Calculate the average atomic mass of elements X and Z.

( b ) How does the average atomic mass of elements X and Z compare with the atomic mass of element Y ?

( c ) Which law of classification of elements is illustrated by this example ?

( d ) What could the elements X , Y and Z be ?

( e ) Give another example of set of elements which can be classified according to this law .

Ans :- ( a ) 23

( b ) The average atomic mass of elements X and Z is equal to the atomic mass of element Y.

( c ) Dobereiner’s law of triads .

( d ) X is lithium.

Y is sodium.

Z is potassium.

( e ) Chlorine , Bromine , Iodine .

Q.16. Consider the following elements . Comments on om

Na , Ca , AI , K , Mg , Li

( a ) Which of these elements belong to the same period of the periodic table ?

Ans :- Same period : Na, Mg, Al

Q.6. Which of these elements belong to the same group of the periodic table ?

Ans :- Same group Li , Na , k

Q.17. Which element has :

( a ) Two shells , both of which are completely filled with electrons ?

( b ) The electronic configuration 2 , 8 , 2 ?

( c ) A total of three shells , with four electrons in its valency shell ?

( e ) Twice as many electrons in its second shell as its first shell ?

Ans :- ( a ) Neon ( 2, 8 )

( b ) Magnesium.

( c ) Silicon ( 2, 8 , 4 )

( d ) Boron ( 2, 3 )

( e ) Carbon ( 2 , 4 )

Q.18. Mendeleev predicted the existence of certain elements o not known at that time and named two of them as eka aluminium and eka – silicon.

( a ) Name the element which has taken the place of

( i ) Eka aluminium and

( ii ) Eka silicon .

( b ) Mention the period / periods of these elements in the modern periodic table .

( c ) Write the group groups of these elements in the moderns periodic table .

( d ) Classify these elements as metals , non – metals or metalloids .

( e ) How many valence electrons are present in the atoms of each of these elements ?

Ans :- ( a ) ( i ) Gallium.

( ii ) Germanium.

( b ) 4th period.

( c ) Gallium 13th group.

Germanium 14th group.

( d ) Gallium – metal.

Germanium – metalloid.

( d ) Gallium – 3

Germanium – 4

Q.19. A part of the early classification of elements has been given below :

H        Li        Be         B          C           N           O

F         Na      Mg        Al         Si          P            S

( a ) Which law of classification of elements is illustrated by the above arrangement of elements ?

( b ) Name the scientist who proposed such a classification on of elements .

( c ) Why is such a classification of elements compared with a characteristic of musical scale ?

( d ) State one limitation of this classification of elements.

Ans :- ( a ) Newlands ‘ law of octaves.

( b ) Newlands.

( c ) Because in this classification , the repetition in the properties of elements is just like the repetition of eight note in an octave of music .

( d ) This could be applied only up to the element calcium and not beyond that.

Q.20. A metal X is in the first group of the periodic table. What will be the formula of its oxide ?

Ans :- X₂O

Q.21. An element A from group 14 of the periodic table combines with an element B from group 16.

( i ) What type of chemical bond is formed ?

( ii ) Give the formula of the compound formed .

Ans :- ( i ) Covalent bond.

( ii ) AB₂

Q.22. An element X from group 2 of the periodic table reacts with an element from group 17 form a compound.

( a ) What is the nature of the compound formed ?

( b ) State whether the compound formed will conduct electricity or not.

( c ) Give the formula of the compound formed.

( d ) What is the valency of element X ?

( e ) How many electrons are there in the outermost shell of an atom of element Y ?

Ans :- ( a ) Ionic compound.

( b ) Yes.

( c ) XY₂

( e ) 2

( d ) 7

Q.23. An element A has an atomic number of 6. Another element B has 17 electrons in its one neutral atom.

( a ) In which groups of the periodic table would you except to find these elements ?

( b ) What type of bond is formed between A and B ?

( c ) Suggest a formula of the compound formed between A and B

Ans :- ( a ) A in group 14

B in group 17

( b ) Covalent bond

( c ) AB₄

Q.24. An element X is in group 2 of the periodic table :

( a ) What will be the formula of its chloride ?

( b ) What will be the formula of its oxide ?

Ans :- ( a ) XCl₂

( b ) XO

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