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Class 10 Science Chapter 5 Periodic Classification of Elements
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Q.1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of Periodic table .
( a ) The elements become less metallic in nature .
( b ) The number of valence electrons increases .
( c ) The atoms lose their electrons more easily .
( d ) The oxides become more acidic .
Ans :- ( c ) The atoms lose their electrons easily when going left to right is not correct .
Q.2. Element X forms a chloride with the formula Xcl₂ which is solid with a high melting point . X would most likely be in the same group of the Periodic Table as
( a ) Na
( b ) Mg
( c ) AI
( d ) Si
Ans :- ( b ) Mg.
Q.3. 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 valence shell ?
( d ) A total of two shells , with three electrons in its valence shell ?
( e ) Twice as many electrons in its second shell as in its first shell ?
Ans :- ( a ) Ne ( 2, 8 )
( b ) Mg
( c ) Si (2, 8, 4)
( d ) B (2, 3)
( e ) C (2, 4)
Q.4. ( a ) What property do all elements in the same column of the periodic table as born have in common ?
( b ) What property do all elements in the same column of the periodic Table as fluorine have in common ?
Ans :- ( a ) They have the same valence and are metalloids.
( b ) They form acidic oxides and have seven electrons in their outermost shells.
Q.5. An atom has electronic configuration 2, 8, 7.
( a ) What is the atomic number of these elements ?
( b ) To which of the following elements would it be chemically similar ? (Atomic numbers are given in parentheses) N (7) F (9) P (15) Ar (18)
Ans :- (a) The atomic number of the element = 2 + 8 + 7
(b) F (9) Because the noof electrons of the outermost shell of F is 7
Q.6. The position of three elements A, B, and C in the Periodic Table are shown below :
Group 16 Group 17
( a ) State whether A is a metal Or non metal.
( b ) State whether C is more reactive or less reactive that A.
( c ) Will C be larger or smaller in size than B ?
( d ) Which type of ion , cation or anion will be formed by element A ?
Ans :- ( a ) Element A is in group 17. Now , group 17 is on the right side or the periodic table where non – metals are placed . So, element A is a non – metal .
( b ) In group 17 of halogens , the chemical reactivity decreases on going down in a group . Thus element C will be less reactive than element A.
( c ) On going from left to right in a period , the size of atoms , decreases . So , the atom of C will be smaller in size than an atom of B.
( d ) Element A of group 17 has 7 valence electrons . So, it will accept 1 electrons to form a negatively charged ion , A. The negatively charged ion is called anion . Thus , element A will form an anion .
Q.7. Nitrogen ( atomic number 7 ) and phosphorus ( atomic number 15 ) belong to group 15 of the Periodic Table . Write the electronic configuration A 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 outermost shell is nearer to nucleus .
Q.8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table ?
Ans :- The position of an atom in the periodic table is related to the number of electrons in the outermost shell. In a given column of group , all elements have the same number of electrons in their outermost shells .
Q.9. In the Modern Periodic Table , Calcium ( atomic number 20 ) is surrounded by elements with atomic numbers 12 , 19 , 21 , and 38. Which of these have physical and chemical properties resembling calcium ?
Ans :- The electronic configuration of calcium = 2, 8, 8, 2
The electronic configuration of atomic number 12 = 2 , 8, 2
The electronic configuration of atomic number 19 = 2 , 8, 8 , 1
The electronic configuration of atomic number 21 = 2 , 8, 8, 3
The electronic configuration of atomic number 38 = 2 , 8, 18 , 8, 2
Elements with atomic number 12 38 will have similar physical and chemical properties as calcium .
Q.10. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and Modern Periodic Table .
|Mendeleev’s Periodic Table||Modern Periodic Table|
|1. Mendeleev’s periodic table is based on atomic masses of based on atomic number of elements .||1. Modern periodic table is based on atomic number of elements .|
|2. Mendeleev’s periodic table does not explain the reason for the periodicity in the properties of elements.||2. Modern periodic table says that since the electronic configurations of elements are repeated at regular intervals therefore , the properties, of elements are also repeated at regular intervals.|
|3. There are nine vertical columns called groups .||3. There are eighteen vertical columns called groups.|
|4. Mendeliev’s periodic table had a number of defects .||4. There are no defeats in the modern periodic table .|
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