NCERT Solutions Exercise
Q1. 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.
Answer: (c) The atoms lose their electrons more easily.
Q2. Element X forms a chloride with the formula XCl2, which is a 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
Answer: (b) Mg
Q3. 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?
Answer: (a) Neon (Ne)
(b) Magnesium (Mg)
(c) Silicon (Si)
(d) Boron (B)
(e) Carbon (C)
Q4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer: (a) Similar properties :-
(i) All elements are metals.
(ii) Coming down from top to bottom, the metallic properties increase.
(iii) All are good conductors of electricity.
(b) Similar properties :-
(i) All elements are non-metals and valency is 7.
(ii) All are bad conductors of electricity.
Q5. An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(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)
Answer: (a) Its atomic number is 17.
(b) There will be similarity in chemical properties with F(9) - 2,7.
Q6. The position of three elements A, B and C in the Periodic Table are shown below –
Group 16 Group 17
_ _
_ A
_ _
B C
(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than 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?
Answer: (a) A- is a non-metal.
(b) C is less active.
(c) the size of C is smaller than that of B
(d) Element A will form anion.
Q7. 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?
Answer: The atomic number of nitrogen is 7 (2,5) so it will be more electronegative. Phosphorus and Nitrogen are both non-metals but Phosphorus 15(2,8,5) comes down from nitrogen and thus becomes negative.
Q8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer: Elements are classified according to their electronic configuration. The electron present in the outermost shell of an element gives its valency and the total number of shells is its periodic number.
Q9. 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?
Answer: C(20) is surrounded by elements with atomic numbers 12, 19, 21 and 38 in the periodic table. Out of these, the elements with atomic number 21 (2,8,9,2) and atomic number 38 (2,8,18,2) will have the same chemical and physical properties.
Q10. Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.
Answer:Modern Periodic Table :-
(i) It is ordered according to atomic number.
(ii) It has 18 squares.
(iii) In these inert gases are kept in the 18th class.
Mendeleev's periodic table:-
(i) It is based on atomic mass.
(ii) It has 8 groups.
(iii) There is no place for inert gases in them.
