Page 141 - Chemistry ICSE Class IX

The Periodic Table 129
Q.10. A part of the periodic table is shown below. Please note, here the groups are numbered on the basis of short form
periodic table.
1 2 3 4 5 6 7 0
Lithium Carbon Oxygen L Neon
X E G Q
Y R
Z T
Answer the following:
(a) Give the letter of the most reactive metal.
(b) Give the letter of the most reactive nonmetal.
(c) Name the family of elements represented by L, Q, R, T.
(d) Name one element in each case occurring in group 2, 3 and 5.
Ans. (a) The element at the bottom of the group on the extreme left is the most reactive element. So, Z is the most
reactive metal.
(b) The element at the top of the group on the extreme right is the most reactive nonmetal. So, the element L is
the most reactive nonmetal.
(c) L, Q, R, T belong to group 7. These elements are the members of the halogen family.
(d) The rst element in group 2, 3 and 5 are Beryllium, Boron and Nitrogen, respectively.
Q.11. Elements having atomic numbers 3 to 18 are shown in the form of a table by using certain letters of the alphabet:
(these letters are not the usual symbols of these elements).
3 4 5 6 7 8 9 10
A G
11 12 13 14 15 16 17 18
B C D F
(a) Which of these is
(i) a noble gas (ii) a halogen (iii) an alkali metal (iv) an element with valency 4?
(b) Write the formula of the compound formed when A reacts with F.
(c) Write the electronic con guration of element G.
Ans. (a) (i) The element G (atomic no. 10) has the electronic con guration 2, 8. Thus, its outermost shell is completely
lled. So, it is a noble gas.
(ii) The element F (at. no. 17) is a member of halogen family.
(iii) Both the elements A and B are alkali metals.
(iv) The element D has the electronic con guration 2, 8, 4. So, its valency is 4. Therefore, the element D has a
valency of 4.
(b) The element A (at. no. 3) has the electronic con guration 2, 1. The element F (at. no. 17) has the electronic
con guration 2, 8, 7. So, the element A has to lose one electron, and the element F has to gain one electron to
attain stable electronic con gurations. By doing so, A becomes a positive ion and F becomes a negative ion.
A o A + + e –
–
F + e o F –
These positive and negative ions combine to give a compound AF.
+ –
–
A + + F o A F o AF
So, the formula of the compound formed is AF.
(c) G has atomic number 10. So, the electronic arrangement in G is 2, 8.
Q.12. Fill in the blanks:
In its modi ed form, the __________ is an organisation of all the known elements, arranged in order of increasing
__________ . Elements that lie in the same __________ have similar __________ , have the same number of
__________ . The table is particularly useful for predicting the outcome of chemical reactions between __________
since an atom of any element tends to react so as to convert its electronic structure to that of a nearby _________ .