Answer question numbers 3(a) - 3(d) on the basis of your understanding of the following paragraph and the related studied concepts:
Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.
The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements.
However, Mendeleev's classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.
3(a) State Mendeleev's Periodic Law.
3(b) Why did Mendeleev leave some gaps in the Periodic table?
3(c) If the letter 'R' was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as:
(i) ,
(ii) ,
(iii) ,
(iv) ,
3(d) Isotopes are:
(i) Atoms of an element with similar chemical properties but different atomic masses.
(ii) Atoms of different elements with similar chemical properties but different atomic masses.
(iii) Atoms of an element with different chemical properties but same atomic masses.
(iv) Atoms of different elements with different chemical properties but same atomic masses.
Answer question numbers 3(a) - 3(d) on the basis of your understanding of the following paragraph and the related studied concepts:
Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.
The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements.
However, Mendeleev's classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.
3(a) State Mendeleev's Periodic Law.
3(b) Why did Mendeleev leave some gaps in the Periodic table?
3(c) If the letter 'R' was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as:
(i) ,
(ii) ,
(iii) ,
(iv) ,
3(d) Isotopes are:
(i) Atoms of an element with similar chemical properties but different atomic masses.
(ii) Atoms of different elements with similar chemical properties but different atomic masses.
(iii) Atoms of an element with different chemical properties but same atomic masses.
(iv) Atoms of different elements with different chemical properties but same atomic masses.
3(a) Mendeleev's Periodic Law states that the properties of elements are a periodic function of their atomic masses.
3(b) Mendeleev left gaps in his Periodic Table to account for elements that were not yet discovered. He predicted their existence and properties based on the trends in his table.
3(c) Correct Option: (ii) ,
3(d) Correct Option: (i) Atoms of an element with similar chemical properties but different atomic masses.
Marking Scheme
- 13(a) Correct statement of law: 1 mark
- 23(b) Mentioning undiscovered elements/predictions: 1 mark
- 33(c) Selecting option (ii): 1 mark
- 43(d) Selecting option (i): 1 mark
Hint
Recall that Carbon has a valency of 4 and forms Methane and Carbon Dioxide.
Quick Oral Answer
Mendeleev's law is based on atomic mass. He left gaps for elements like Gallium and Germanium. Carbon forms and because it is in Group IV.
Analysis & Explanation
3(a) Mendeleev believed atomic mass was the most fundamental property of an element.
3(b) By leaving gaps, he turned a limitation into a prediction, famously predicting 'Eka-aluminium' (Gallium) and 'Eka-silicon' (Germanium).
3(c) Carbon is in Group IV of Mendeleev's table. Elements in this group have a valency of 4. Therefore, they form hydrides of the type (like ) and oxides of the type (like ).
3(d) Isotopes are atoms of the same element (same atomic number/protons), which means they have the same electronic configuration and chemical properties, but they differ in the number of neutrons, resulting in different atomic masses. Mendeleev's table struggled with isotopes because it was based on atomic mass.
Common Mistakes
- 1Confusing Mendeleev's Law (atomic mass) with Modern Periodic Law (atomic number).
- 2Thinking isotopes have different chemical properties because their masses are different.
Interesting Facts
Mendeleev was so confident in his table that he suggested some measured atomic masses were wrong because they didn't fit his periodic patterns—and he was often right!
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2020?
This question carries 4 marks in the CBSE Class 10 Science 2020 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Periodic Classification of Elements" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2020 paper?
This question appears in Section A in the CBSE Class 10 Science 2020 paper.