CBSE Class 10 Science Chapter-5 Periodic Classification of Elements Important Questions – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 5 – Periodic Classification of Elements prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Periodic Classification of Elements Chapter-5 Important Questions
CBSE Class 10 science Important Questions Chapter 5 – Periodic Classification of Elements
2 Mark Questions
1. Alkali metals do not form dipositive ions why?
Ans. Alkali metals present in Group 1 so 17 has only one valence electron. By loosing one e– They acquire the configuration of the noble gas element and hence do not form dispositive ions.
2. Why non-metals are called electro negative elements?
Ans. Non-metals are called electronegative elements since their atoms form negative ions by accepting electrons
3. How were the positions of different isotopes decided in the modern periodic table?
Ans. All the isotopes have same atomic numbers in modern periodic table the elements have been allotted places based on their atomic numbers. Therefore, all the isotopes of an element have been assigned the same position in the modern periodic table.
4. Hydrogen is regarded as a rogue element in the periodic table. Discuss.
Ans. Hydrogen is regarded as a rogue element in the periodic table because till today its position is not satisfactory. Although it has been placed on the top of alkali metals on the basis of electronic configuration, but it is non-metal and also resembles halogens of group 17.
5. Why do elements in a group show same valency?
Ans. The valency of an element is related to the valence shall electronic configuration of its atom. Since the elements present in a group have the same valance shell electronic configuration. They show the same valency.
6. Why are the members of group 1 known as alkali metals?
Ans. All the elements in group 1 are known as alkali metals because they react with water to form soluble hydroxides that are called alkalis.
7. How does metallic character of the elements vary (i) In a group (ii) In a period?
Ans. (i) The metallic character of the elements increases downwards in a group
(ii) The metallic character of the elements decreases from left to right is a period.
8. Name other elements which belong to the same family as
(i) Calcium (ii) Carbon.
Ans. (i) Magnesium, Strontium
(ii) Silicon, Germanium.
9. Did Dobereiner’s triads also exist in the columns of Newland’s Octaves? Compare and find out?
Ans. Yes, following triads can be identified:
Li, Na, K
Be, Mg, Ca
The atomic mass of middle atom in the above triads is approximately equal to the average mass of elements on the left and right hand side.
10. What were the limitations of Dobereiner’s classification?
Ans. Debereneiner could identify only three triads from the elements known at that time. Hence, this classification of elements was not found to be useful.
11. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Ans. Scandium and Germanium.
12. How could the Modern Periodic table remove various anomalies of Mendeleev’s Periodic Table?
Ans. Modern Periodic Table settled the placement of isotopes as isotopes have same atomic number.
Position of controversial position of hydrogen is also settled in modern periodic table.
13. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Ans. Calcium and Strontium would show chemical reactions similar to magnesium. They have the same number of electrons in the outermost shell.
14. In the Modern Periodic Table, which are the metals among the first ten elements?
Ans. Lithium and Beryllium are the metals among the first ten elements in the Modern Periodic Table.
15. (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 common?
Ans. (a) All the elements in the in the same column as boron have three electrons in the valence shell. That is all the elements are trivalent.
(b) All the elements in the same column as fluorine has one electron in the valance shell, which is all the elements, are monovalent.
16. 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)
Ans. Chlorine has the electronic configuration 2, 8, 7.
(a) Atomic number of element is 17.
(b) F (9)
17. 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?
Ans. Nitrogen atomic number 7 has got 7 electrons with electronic configuration 2, 5.
Phosphorus with atomic number 15 has got 15 electrons with electronic configuration 2, 8, 5.
Non-metallic character decreases as we move down the group. Therefore, nitrogen will be more electronegative than phosphorus.
18. In the modern Periodic Table calcium (atomic number 20) is surrounded by elements with atomic number 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?
Ans. Elements in a group have similar properties. Elements with atomic numbers 12 and 38 lie in the same group as calcium. Therefore, they will have properties resembling calcium.
19. A metal M forms an oxide having the formula M203. It belongs to 3 period in the modem periodic table. Write the atomic number and valency of the metal.
Ans. Atomic number=13
Valency = 3
