Some More Written Practice Questions

Question.1

The elements of the second period of the Periodic Table are given below:
Li Be B C N O F
(a) Give a reason to explain why atomic radii decrease from Li to F.
(b) Identify the most
(i) metallic and
(ii)non-metallic element.


Answer.
(a) It is because nuclear charge increases due to an increase in atomic number, therefore, the force of attraction between nucleus and valence electrons increases, i.e. effective nuclear charge increases, hence atomic radii decrease from Li to F.
(b) (i) Most metallic element is ‘Li’ as it
can lose electrons easily due to the larger atomic size.
(ii) Most non-metallic element is ‘F’ because it can gain electrons easily due to smallest atomic size.

Question.2

 What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev’s Periodic Law.


Answer. Atomic mass as a physical property and nature and formulae of oxide and hydride formed, and chemical property was used by Mendeleev.
Following are the two observations which posed a challenge to Mendeleev’s Periodic Law.
(i) Increasing order of atomic weights could not be maintained while matching chemical properties. Chemical properties do not depend upon atomic mass.
(ii) Isotopes have different atomic mass but same chemical properties.

Question.3

(a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
(e) Would you place the two isotopes ‘ of chlorine, CI-35 and CI-37 in
different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.


Answer.
(a) It is done so as to study the properties of elements conveniently.
(b) Increasing order of atomic mass and similarities in chemical properties (especially nature and formulae of oxide and hydride formed).
(c) These gaps were left for undiscovered elements.
(d) Noble gases were not invented at that time.
(e) They will be kept at same slot as they have same chemical properties.

Question.4

 State Mendeleev’s periodic law. Write two achievements of Mendeleev’s periodic table


Answer. Mendeleev’s Periodic Law: ‘Properties of elements are the periodic function of their atomic masses.
Achievements:

  1.  It could classify all the elements discovered at that time.
  2. It helped in discovery of new elements.
  3.  It helped in correction of atomic mass of some of the elements.

Question.5

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

  1.  To which group or period of the Periodic Table do the listed elements belong?
  2.  What would be the nature of compound formed by a combination of elements B and F?
  3.  Which two of these elements could definitely be metals?
  4.  Which one of the eight elements is most likely to be found in gaseous state at room temperature?
  5.  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.

Answer.

  1. A and B belong to group 1 and 2 because they form basic oxides. C belongs to group 13 as it has 3 valence electrons. D belongs to group 14 as it forms almost neutral oxide. E and F belong to group 15 and 16 as they form acidic oxides, G belongs to group 17 as it has 7 valence electrons and H belongs to group 18. They belong to the 3rd period of the Periodic Table because AG is NaCI, added in a small amount to almost all vegetable dishes during cooking, and Na and Cl belong to the 3rd period.
  2. Ionic compounds will be formed because ‘B’ is metal and ‘F’ is non-metal. ‘B’ can lose two electrons and ‘F’ can gain two electrons.
  3. A and B are definitely metals as they form basic oxides.
  4. G and H are gaseous at room temperature.
  5.  CG3 is the formula of the compound formed by a combination of C and G.