Page 154 - Chemistry ICSE Class IX

142 ICSE Chemistry – 9
(a) rst period

(b) second period
(c) third period?
Based upon this, predict the maximum number of elements which could be placed in these periods.
12. On the basis of electronic con guration, how will you identify
(a) the rst element of a period
(b) the last element of a period
(c) an element of the oxygen group
(d) a noble gas element?
13. Describe the basic character of the oxides of 3rd period elements across the period.
14. Name the properties of the elements which
(a) increase while going from left to right in a period.
(b) decrease while going from left to right in a period.
(c) increase while going from top to bottom in a group.
(d) decrease while going from top to bottom in a group.
15. By giving suitable examples, prove that all the elements of a group show similar properties, while the properties
of the elements in a period show a gradual change.
16. Given below are the electronic con gurations of some elements:
(a) 2, 8, 3 (b) 2, 8, 18, 5 (c) 2, 8, 7 (d) 2, 8, 18, 8, 1
(e) 2, 8, 2 (f) 2, 5 (g) 2, 8, 18, 8
Answer the following:
(i) To which group does each belong? (ii) To which period does each belong?

(iii) Which is an inert gas? (iv) Which is an alkali metal?
(v) Which is a halogen? (vi) Which elements belong to the same group?
(vii) Which is the rst element of a period? (viii) Which elements belong to the same period?
17. Give one example of the element discovered after Mendeleev’s Periodic Table.
18. An element ‘X’ is in the third group of the periodic table. What is the formula of its oxide?
19. Use the Mendeleev’s periodic table to predict the formulae for the oxides of following elements:
K, C, Al, Si, Ba
20. Beside Gallium, which other elements have since been discovered to ll the gaps left by Mendeleev in his periodic
table? Name any two.
21. Explain why the properties of the 8th element are repeated in case of elements arranged in 2nd and 3rd period
of the long form of the periodic table.

22. Why is silicon tetravalent, while chlorine is monovalent?
23. What do you understand by the term periodicity? Are the properties of the elements placed in a group same?
Illustrate.
24. How do the electronic structures of the atoms relate to their position in the modern periodic table?
25. Tick (9) the correct answer.
(i) All the elements in a group of the periodic table have the same
(a) atomic number ˆ
(b) mass number ˆ
(c) number of valence electrons ˆ
(d) number of electrons ˆ