Chapter wise test-Periodic Classification of elements
2 Marks Questions [2 x 5 = 10 ]
1. An element has electronic configuration 2, 8, 3. What is the atomic number of this element? To which (i) group and (ii) period this element belong?
2. State the positions of (i) isotopes of the same element and (ii) hydrogen in the Modern Periodic Table.
3. How does the tendency to gain electrons change as we go down the 16th group of periodic table? Why?
4. 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)
5. (a) State the Modern Periodic Law. (b) Name the element which has twice as many electrons in its second shell as in its first shell. Write its electronic configuration also.
3 Marks Questions [ 3 x 5 = 15 ]
1. An element X belongs to group 17 and third period of the periodic table. (a) Write electronic configuration of the element. What is its valency? (b) Predict its nature, whether it is a metal or non-metal. (c) Give the formula of the compound formed when it combines with an element Y having valency three.
2. Three elements A, B and C have atomic number 7, 8 and 9 respectively. (a) What would be their positions in the Modern Periodic Table (Mention group and period both)? (b) Arrange A, B and C in the decreasing order of their size. (c) Which one of the three elements is most reactive and why?
3. (a) The elements of the second period along with their atomic number in parenthesis are given below : B (5), Be (4), O (8), N (7), Li (3), C (6), F (9) (i) Arrange them in the same order as they are in the periodic table. (ii) Which element has the (i) largest (ii) smallest atom? (b) Why does the atomic radius change as we move from left to right in a period?
4. (a) How is the valency of an element determined from its position in the periodic table? (b) Magnesium has atomic number 12. To which (i) group (ii) period of the periodic table does it belong? (c) The valency of all the elements in a group is same. Why?
5. A part of the periodic table has been shown below :
Answer the following questions on the basis of position of elements in the above table.
(a) Which element is a noble gas? Give reason.
(b) Which element is most electronegative? Give reason.
(c) Write the electronic configuration of (i) B and (ii) E.
5 Marks Questions [ 5 x 1 = 5]
1. What are electron affinity and ionization energy? How they are vary in group and periods in modern periodic table? OR, Two elements ‘A’ and ‘B’ belong to group 1 and 2 respectively in the same period. Compare them with respect to :– (a) Number of valence electrons (b) Valency (c) Metallic character (d) Size of atom (e) Formulae of their oxides.
1. Atomic number is 13. (i) Group – 13 (ii) 3rd Period
2. (i) All isotopes have same atomic number. So they have same place for a particular element.
(ii) Hydrogen is not given a definite position. It was placed in group I A and group VII B in the Modern Periodic Table.
3. As we go down the 16th group of periodic table, tendency to gain electrons decreases because the electronegative character (non metallic character) of elements gradually decreases.
4. As we move down in a group, an electron shell is added after every change of period. Sodium has one more shell than lithium.
Li (3) = 2, 1
Na (11) = 2, 8, 1
Due to less number of shells, lithium atom is smaller than sodium atom.
(b) The nucleus of chlorine has more tendency to attract an extra electron than the nucleus of sulphur because chlorine needs only one 1 electron to complete its shell. Hence, chlorine is more electronegative than sulphur.
5. (a) Modern Periodic Law : Properties of elements are the periodic function of their atomic numbers.
(b) Carbon (atomic number 6) has twice electrons in its second shell as compared to first shell because its electronic configuration is 2, 4.
3 Marks Questions
1. (a) Electronic configuration — 2, 8, 7. Its valency is one. (b) It is a non-metal (c) YX3
2. (a) A, B and C occupy 2nd period of periodic table and 15, 16 and 17 groups respectively.
(b) A > B > C because atomic size decreases as we move from left to right across a period.
(c) C has electronic configuration 2, 7. It needs only one electron to complete its outermost shell. So it is more reactive.
3(a) (i) Li (3), Be (4), B (5), C (6), N (7), O (8), F (9).
(ii) Li is largest and F is smallest atom.
(b) As one moves from left to right across a period, there is a consecutive addition of a proton
in the nucleus that increases the positive charge, which consequently pulls the extra nuclear electrons in the outermost shell inward. Thus, atomic size decreases with the increase in the number of protons as one moves from left to right in a period.
4. (a) The valency of an element with respect to hydrogen increases from 1 to 4 and then falls to 1 as in 2nd period elements.
The valency of elements with respect to oxygen increases from 1 to 7 for 3rd period elements.
(b) (i) 2nd group (ii) 3rd period
(c) In a group all elements have same number of electrons in their outermost shell. So they have same valency.