CBSE Class 10 Science Periodic Classification Of Elements Assignment Set D

Question. According to Mendeleev periodic table, the physical and chemical properties of elements are periodic function of their:
(a) Atomic Mass
(b) Atomic Numbers
(c) Atomic Volumes
(d) Densities

Answer: A

Question. Group-2 Metals are referred to as:
(a) Alkali Metals
(b) Alkaline earth Metals
(c) Chalcogens
(d) Halogens

Answer: B

Question. Which of the following elements would lose an electron easily?
(a) Mg
(b) Na
(c) K
(d) Ca

Answer: C

Question. Which of the following elements does not lose an electron easily?
(a) Na
(b) F
(c) Mg
(d) Al

Answer: B

Question. Elements P, Q, R and S have atomic numbers 11, 15, 17 and 18 respectively. Which of them are reactive non‑metals?
(a) P and Q
(b) P and R
(c) Q and R
(d) R and S

Answer: C

Very short answer Type Questions :

Question. On moving from left to right in the second period, what happens to the number of valence electrons?
Answer: Valence electrons keeps on increasing from left to right in the second period.

Question. What is place of metalloid in the periodic table?
Answer: They are placed between metals and non‑metals in a zig‑zag manner.

Question. Arrange the following metals in decreasing order of atomic size: Ca, Mg, Ba, Be 
Answer: Ba > Ca > Mg > Be

Question. Give any one difference in the electronic configuration of Group 1 and Group 2 elements.
Answer: Group 1 elements have 1 valence electron and are more reactive than Group 2 elements which have two valence electrons.

Question. To which group and period should hydrogen be assigned? 
Answer: It is placed in Group 1 and first period.

Question. Why was the system of classification of elements into triads not found suitable?
Answer: It is because all the elements discovered at that time could not be classified into triads.

Question. An element ‘X’ belongs to the second group of periodic table. What is the formula of its chloride?
Answer: XCl₂

Question. Where would you expect to find the element with atomic number 18 in the periodic table?
Answer: The element will bein-18th group and in the 3^rd period of the periodic table.

Question. Name the elements present in first period.
Answer: Hydrogen and Helium.

Question. Give the number of elements in 2nd and 5th period of modern periodic table. 
Answer: 2nd period has 8 elements, 5th period has 18 elements.

Question. An element ‘A’ has atomic number 16. To which group and period does it belong? 
Answer: It belongs to group 16 and third (3rd) period.

Question. Where would you locate the element with electronic configuration: 2, 8 in the modern periodic table?
Answer: It belongs to Group 18 and second period of the periodic table.

Question. What was the basis of classification of elements by Newlands?
                          OR
Define Newlands’ law of octaves.
Answer: Elements were arranged in increasing order of atomic mass and every 8th element resembled with the first element.

Question. Write the formulae of chlorides of Eka‑silicon and Eka‑aluminium, the elements predicted by Mendeleev.
Answer: GeCl₄, GaCl₃.

Question. Out of the three elements P, Q and R, having atomic number 11, 17 and 19 respectively, which two elements will show similar properties and why? 
Answer: P(11): 2, 8, 1, Q(17): 2, 8, 7, R(19): 2, 8, 8, 1
‘P’ and ‘R’, because they have the same number of valence electrons.

Question. Write the number of horizontal rows in the modern periodic table. What are these rows called?
Answer: There are 7 horizontal rows. These are called periods.

Short Answer Questions

Question. Give reasons for the following:
(a) Lithium atom is smaller than sodium atom.
(b) Chlorine (Atomic number 17) is more electronegative than sulphur (Atomic number 16).
Answer: (a) It is because Li(2, 1) has two shells whereas Na(2, 8, 1) has three shells.
(b) Chlorine is smaller in size and has more effective nuclear charge than sulphur, therefore it is more electronegative.

Question. 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:
(a) size of their atoms (b) their metallic characters
(c) their valencies in forming oxides (d) formulae of their chlorides 
Answer: (a) Size of ‘N’ is smaller than ‘M’.
(b) ‘M’ is more metallic than ‘N’.
(c) Valency of ‘M’ is 1 and valency of ‘N’ is 2.
(d) MCl and NCl₂ are the formulae of their chlorides.

Question. In the following table, the position of six elements A, B, C, D, E and F are given as they are in the modern periodic table as follows:

On the basis of above table, answer the following questions: 
(i) Name the element which form only covalent compounds.
(ii) Name the element which is a metal with the valency of 3.
(iii) Name the non‑metal with the valency of 3.
(iv) Out of B and C, whose atomic size is bigger and why?
(v) Write the common name for the family to which the elements D and F belongs to.
Answer: (i) E, (ii) B, (iii) C, (iv) B, … It has more number of shells, (v) Noble gases

Question. Based on the group valency of elements, state the formula of the following, giving justification for each.
(i) Oxides of Group 1 elements.
(ii) Halides of the elements of Group 13.
(iii) Compounds formed when an element of group 2 combines with an element of Group 16.
Answer: (i) Group 1 elements can lose one electron to become stable, so its valency is equal to 1, M2O.
(ii) Group 13 elements have valency equal to 3, MCl3.
(iii) Group 2 elements have valency equal to 2, Group 16 elements have 6 valence electrons.

Question. Study the data of the following three categories A, B and C.

(a) From the given three categories A, B and C, pick the one which forms Dobereiner’s Triads.
(b) Why did Mendeleev placed elements of category A, B and C in three different groups?
(c) Is Newland law of octaves applicable to all the three categories? Give reason to justify your answer.
Answer: (a) ‘A’ forms Dobereiner’s Triad.
(b) It is because they had different formula of oxides and hydrides.
(c) No, it was not applicable to elements after Ca(20) because after Ca every eighth element did not possess similar properties to first.

Question. Choose from the following: 6C, 8O, 10Ne, 11Na, 14Si
(a) Elements that should be placed in the same period.
(b) Elements that should be placed in the same group.
State the reason for your selection in each case.
Answer: (a) 6C, 8O, 10Ne belong to the same period because all these have 2 shells.
11Na, 14Si belong to the same period because both of these have 3 shells.
(b) 6C and 14Si belong to the same group because they have the same number of valence electrons and valency.