Friday, 30 October 2015

TEXTBOOK ANSWERS AND SOLUTIONS CBSE CLASS X SCIENCE Chapter-5 Periodic Classification of elements



Exercise question and answers


1) Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table?
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.

ANSWER: - The atoms lose their electrons more easily.

2) Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na (b) Mg (c) Al (d) Si

ANSWER:-b) Mg

3) Which element has

(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?

ANSWER:-

(a) Neon has two shells, both of which are completely filled with electrons (2 electrons in K shell and 8 electrons in L shell).
(b) Magnesium has the electronic configuration 2, 8, 2.
(c) Silicon has a total of three shells, with four electrons in its valence shell (2 electrons in K shell, 8 electrons in L shell and 4 electrons in M shell).
(d) Boron has a total of two shells, with three electrons in its valence shell (2 electrons in K shell and 3 electrons in L shell).
(e) Carbon has twice as many electrons in its second shell as in its first shell

4) (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 in common?

ANSWER:-

a)    All the elements in the same column as boron have the same number of valence electrons (3).
b)    All the elements in the same column as fluorine have the same number of valence electrons (7). Hence, they all have valency equal to 1.

5) 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)

ANSWER:-
(a) The atomic number of this element is 17.
(b) It would be chemically similar to F(9) with configuration as 2, 7.

6) The position of three elements A, B and C in the Periodic Table are shown below

Group 16       Group 17
………….
…………. A
………….
B …………. C
(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?

ANSWER:-
(a) A is a non-metal.
(b) C is less reactive than A, as reactivity decreases down the group in halogens.
(c) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore, electrons come closer to the nucleus.
(d) A will form an anion as it accepts an electron to complete its octet.

7) Nitrogen (atomic number 7) and phosphorus (atomic number15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?

ANSWER:-Nitrogen .. 2 5
Phosphorus. 2 8 5
Nitrogen is more electronegative than phosphorus. As we move down in a group the number of shells gradually increases therefore valence electrons move away from the nucleus and the effective nuclear charge decreases. This causes the decrease in the tendency to attract electron and hence electro negativity decreases.

8) How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

ANSWER:-In the modern periodic table, atoms with similar electronic configurations are placed in the same column.

9) In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?

ANSWER:-The element with atomic number 12 has same chemical properties as that of calcium.

10) Compare and contrast the arrangement of elements in Mendeleevs periodic Table and the Modern Periodic Table

ANSWER:-



Written By Badal Paul
The author is a passionate blogger, writer and educationalist. This blog is created to ease troubles of the Cbse students. The author holds multiple blogs and the writer of the Novel KALCHAKRA, OOM AND THE CHOSEN FIVE.