Chhattisgarh State Class 10 Science Chapter 4 Periodic Classification of Elements Solution
1) Choose the correct option–
(i) The position of which of the following elements is not fixed in the periodic elements
(a) Sodium (b) Chlorine
(c) Helium (d) Hydrogen.
Ans: – (d) Hydrogen.
(ii) Elements in Mendeleev’s periodic table have been arranged according to–
(a) Increasing order of molecular weight
(b) Increasing order of atomic weight
(c) Increasing order of atomic number
(d) Increasing order of atomic radii.
Ans: – (b) Increasing order of atomic weight.
(iii) The modern periodic law was proposed by–
(a) Newlands (b) Moseley
(c) Mendeleev (d) Döbereiner.
Ans: – (b) Moseley.
(iv) On moving down a group, the metallic character–
(a) Neither increases nor decreases (b) decreases
(c) Increases (d) First increases, then decreases.
Ans: – (c) Increases.
(v) Which of the following depicts increasing atomic sizes of Na, Li, K –
(a) Li<Na<K (b) K<Na<Li
(c) Na<Li<K (d) None of the above.
Ans: – (a) Li< Na < K.
2) The physical and chemical properties of elements belonging to the same group are similar, why?
Ans: – As we all know that in a same group all element has same no of valence electron in their last shell. From the periodic law we came to know that same valence electron shows same physical and chemical properties so for this reason all the element in a group show’s similar properties.
3) Hydrogen should be placed in which group and which period? Give reasons.
Ans: – Hydrogen shows different types of properties such as it has similar properties like the alkali metal as both have same no of valence electron in their last shell. If we compare the hydrogen with halogen compound it also diatomic in nature. So there is debate of its position in the periodic table but it kept in 1st group according to its electronic configuration.
4) In each of the given pairs, choose which element will have the bigger atom. Give reasons for your choice.
(a) Mg (atomic number 12) or Cl (atomic number 17)
(b) Na (atomic number 11) or K (atomic number 19).
Ans: –
- In periodic table the size of an element decreases when we go from left to wright so comparing this Mg will be bigger to Cl.
- In a group when we go from up to down the atomic sizes of an element is increases so K will be bigger as compare to sodium.
5) The atomic numbers of three elements A, B and C are 5, 7 and 10 respectively. Which two of these will have similar properties? Give reasons.
Ans: – From the electronic configuration of A (2,3) , B( 2, 5), C (2,8) we can see that both A and B elements have same no valence electron in their last shell. As we all know which elements have same no of valence electron show’s similar property so here A and B will show same property.
6) The atomic numbers of three elements are 5, 7 and 10 respectively. Which of these:
(a) Belongs to group 18
(b) Belongs to group 15
(c) Belongs to group 13.
Ans: – (a) Here the atomic no 10 represent the element neon which is a Noble gas . As we all know all noble gas are kept in group 18.
(b) Atomic no 7 or Nitrogen belong to group 15.
(c) Atomic no 5 or Boron belongs to the group 13.
7) ‘A’, ‘B’ and ‘C’ are three elements that form a triad. If the atomic weight of ‘A’ is 7 and that of ‘C’ is 39 then according to Döbereiner rule of triads what will be the atomic weight of ‘B’?
Ans: – From the Doberniar triad rules we came to know that the atomic weight of the middle element is the average of the some of the remaining two elements. So the atomic weight will be ( A + C)/2 or (7 + 39 / 2 = 23) 23 which is sodium.
8) The figure shows a part of the periodic table:
| Li | Be | B | C | N | O | F |
| Na | Mg | Al | Si | P | S | Cl |
If we have horizontally from left to right
(i) How does the metallic character of the elements change?
(ii) How does electronegativity change?
(iii) How does electron affinity change?
Ans: – (i) In a period when we go from left to right the metallic character decrease so from Li to F the or Na to Cl the metallic character will decrease.
(ii) In a period moving Left to right the electronegativity will increase. Here F is most electronegative element.
(iii)The electron affinity is increases when we go left to right in a period so the electron affinity will increase from Li to F and Na to Cl.
9) Why did Mendeleev leave gaps in his periodic table? Use an example to illustrate your answer.
Ans: – The arrangements of the Mendeleev periodic table are according to the atomic masses of elements. So, he kept different types of elements according to their increasing atomic weight and also showing similar properties in a group. When he doesn’t find any element of similar properties, he thought in future it will be discovered so he leaves gap. Germanium is the element which discovered at last and fill the gap.
10) Are Döbereiner’s triads seen in Newlands’ octets? Compare and write.
Ans: – Yes Döbereiner triad seen in Newland octets rules for example the elements Na, K and Li which is a proper example of Döbereiner is also shows the property of Newland octets rules. The Newland octet rules say that eight consecutive element shows the same properties while Döbereiner States that the middle element of the mean of first and last element in three elements series shows similar properties.
11) Give the trends shown by the following properties when we go down a group or from left to right in a period in the modern periodic table – valency, atomic size, ionization potential, electronegativity.
Ans: – Valency: – In a period the valency in increases up to 4th period then decrease. But in a group valency is same.
Atomic size: – In a period from left to right atomic size is decrease and, in a group, atomic size is increases from to bottom.
Ionization potential: – IP value in increases from left to right in a period. And down a group it decreases.
Electronegativity: – Electronegativity is increasing from left to right in a period and decreases from top to bottom.
12) The electronic configuration of an element B is 2, 8, 7 and it forms an ionic compound AB2 with another element A. What is the valency of element A?
Ans: – From the electronic configuration of the element B we can say that the valency of B is 1 so for forming the compound AB2 the valency of A must be 2.
13) Compare the arrangement of elements in Mendeleev’s periodic table and the modern periodic table.
Ans: –
Mendeleev periodic table | Modern Periodic table |
| The elements are arranged according to the atomic mases. | The elements are arranged according to the atomic number. |
It has 6 periods and 6 group. | It has 18 groups and 7 periods. |
| Same properties showing elements are kept in same place. | The valency in decided the position. |