Important questions of periodic classification of elements
Answers
It will be :-
Question.1The elements of the second period of the Periodic Table are given below:
Li Be B C N O F
(a) Give reason to explain why atomic radii decrease from Li to F.
(b) Identify the most
(i) metallic and
(ii)non-metallic element.
Question.2 The elements of the third period of the Periodic Table are given below:
periodic-classification-of-elements-chapter-wise-important-questions-class-10-science-1
(a) Which atom is bigger, Na or Mg? Why?
(6) Identify the most (i) metallic and (ii) non-metallic element in Period 3.
Question.3 The position of three elements A, B and C in the Periodic Table is shown below:
periodic-classification-of-elements-chapter-wise-important-questions-class-10-science-2
Giving reasons, explain the following:
(a) Element A is a non-metal.
(b) Element B has a larger atomic size than element C.
(c) Element C has a valency of 1
Question.4 The position of three elements A, B and C in the Periodic Table is shown below:
periodic-classification-of-elements-chapter-wise-important-questions-class-10-science-3
Giving reasons, explain the following:
(a) Element A is non-metal.
(b) Atom of element C has a larger size ‘ than atom of element A.
(c) Element B has a valency of 1.
Question.5 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.
Question.6 Table given below shows a part of the Periodic Table.
periodic-classification-of-elements-chapter-wise-important-questions-class-10-science-4
(b) Atomic size of Mg is less than that of Na.
(c) Fluorine is more reactive than Chlorine.
Question.7(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.
Question.8 Lithium, sodium and potassium form a Dobereiner’s triad. The atomic masses of lithium and potassium are 7 and 39 respectively. Predict the atomic mass of sodium.
Question.9 Chlorine, bromine and iodine form a Dobereiner’s triad. The atomic masses of chlorine and iodine are 35.5 and 126.9 respectively. Predict the atomic mass of bromine.
Question.10 Why was the system of classification of elements into triads not found suitable?
Question.11 State Mendeleev’s periodic law. Write two achievements of Mendeleev’s periodic table
Question.12 (a) What is meant by periodicity
in properties of elements with reference to the periodic table?
(b) Why do all the elements of the same group have similar properties?
(c) How will the tendency to gain electrons change as we go from left to right across a period? Why?
Question.13 (a) What are ‘groups’ and ‘periods’ in the ‘periodic table’?
(b) Two elements M and N belong to group I and II respectively and are in the same period of the periodic table. How do the following properties of M and N vary?
1. Sizes of their atoms
2. Their metallic characters
3.Their valencies in forming oxides
4. Molecular formulae of their chlorides
Question.14 (a) Which two criteria did Mendeleev use to classify the elements in his Periodic Table?
(b) State Mendeleev’s periodic law.
(c) Why could no fixed position be given to hydrogen in Mendeleev’s Periodic Table?
(i) Sizes of their atoms
(ii) Their metallic characters
(iii) Their valencies in forming oxides
(iv) Molecular formulae of their chlorides
(a) The vertical columns in the periodic table are called ‘groups’. The horizontal rows in the periodic table are called ‘periods’.
(b) (i) ‘M’ and ‘N’ belong to same
period but group I and II. Therefore, ‘N’ will be smaller than ‘M’ as atomic size goes on decreasing from left to right.
(ii) ‘M’ is more metallic than ‘N’. Metallic character goes on decreasing from left to right as tendency to lose electrons decreases due to decrease in atomic size.
(iii) Their valencies are 1 and 2 respectively in forming oxides. Valency goes on increasing first
and then decreases.
(iv) MCI, NCI2 are molecular formulae of their chlorides.
(d) How and why does the atomic size vary as you go
(i) from left to right along a period?
(ii) down a group?
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Answer:
The elements of the second period of the Periodic Table are given below:
Li Be B C N O F
(a) Give 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 increase in atomic number, therefore, 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 larger atomic size.
(ii) Most non-metallic element is ‘F’ because it can gain electrons easily due to smallest atomic size.
Question.2 The elements of the third period of the Periodic Table are given below:
1- Na, 2- Mg, 3-Al, 4- Si, 5-P, 6-S, 7-Cl
(a) Which atom is bigger, Na or Mg? Why?
(6) Identify the most (i) metallic and (ii) non-metallic element in Period 3.
Answer. (a) Sodium is bigger than magnesium as it has lesser nuclear charge so there is less force of attraction between nucleus and valence electrons and less effective nuclear charge. It is, therefore, bigger in size.
(b) (i) Sodium is the most metallic as it can lose electrons easily due to its larger atomic size,
(ii) Chlorine is the most non-metallic element because it can gain electrons easily due to its smallest atomic size.