Periodic classification of elements

1. PERIODIC CLASSIFICATION OF ELEMENTS
1) A) What are ‘groups’ and ‘periods ‘in the periodic table’?
B) Two elements M and N belong to group I and II respectivelyand are
in the same period of the periodic table. How do the following properties
of M and N vary?
i) Their valences in forming oxides
ii) Molecularformulae of their chlorides
Ans. A. The vertical columns in the periodic table are called; groups’. The
horizontal rows in the periodic table are called ‘periods’.
B. i)Their valences are 1 and 2 respectively in forming oxides.
ii) MCl , NCl2 are molecular formulae of their chlorides.
2) Atoms of eight elements A,B,C,D,E,F,G and H have the same number of
electronic shells but different number of electrons in their outermost shells.
It was found that elements A and G combine to form an ionic compound
which can also be extracted from sea water. Oxides of the elements A and
B are basic in nature while those of E and F are acidic. The oxide of
element D is almost neutral. Answer the following questions based on the
information given here in:
1. To which group or period of the periodic table do the listed elements
belong?
2. Which one of the eight elements is likely to be a noble gas?
3. Which one of the eight elements would have the largestatomic radius?
4. Which two elements amongstthese are likely to be non – metals?
5. Which one these eight elements is likely to be a semi- metal or metalloid?
Ans). A and B belong to group 1 and 2 because they form basic oxides. C
belongs to group 13 as it has 3 valence electrons .D belongs to group 14 as it
forms almost neutral oxide. E and F belong to group 15 and 16 as they form
acidic oxides. G belongs to group 17 as it has 7 valiance electrons and H
belongs to group 18 .they belong to 3rd period of periodic Table because sodium
belongs to 3rd period and forms is NaCl, ionic compound of sodium which can
be obtained from sea water and A ( Na) and G ( CI) belong to 3rd period.
2. H is a noble gas.
3. A has the largest atomic radius.
4. E and F are likely to be non-metals and also may be G
5. D is likely to be metalloid or semi – metal.
Q3. The atomic numbers of three elements, X, Y and Z are 9, 11 and 17
respectively. Write their electronic configurations. Whichtwo of these
elements will show similar chemical properties? Why?

2. Ans . Electronic configuration of X, Y and Z will be
X ( 9) : 2, 7
Y (11) : 2,8,1
Z (17) 2,8,7
X and Z will show similar chemical properties as they have same number
of valence electrons.
Q4. Two elements X and Y belong to group 1 and 2 respectivelyin the
same period of periodic table. Compare them with respectto:
1. The number of valence electrons in rtheir atoms
2. their valencies
3. Metallic character
4. the sizes of their atom
Ans
1. X has 1 valence electron, Y has 2 valence electrons.
2. X has valency equal to 1 , Y has valency equal to 2
3. X is more metallic than Y
4. X is bigger than Y
Q5. The atomic number of an element ’S’ is 16. Predict:
1. Number of valence electrons in its atom
2. Its valency
3. Its group number
4. Whether it is a metal or a non – metal
5. The nature of oxide formed by it
6. The formula of its chloride
Ans .The electronic configuration of S (16 ) is 2,8,6
1. 6
2. 2 or 6
3. 16
4. Non metal
5. Acidic oxide
6. SCI2 is a formula of its chloride
Q6. An element ‘X’ has atomic number 13.
(a) Write its electronic configuration
(b) State the group to which ‘X’ belongs
(c) Is ‘X’ is a metal or a non – metal ?
(d) Write the formula of its bromide
Ans. a) 2, 8, 3
b) Group 13
c) ‘X’ is a metal.
d) Formula is XBr3

3. Q7. The atomic numbers of three elements are given below:
Element
(symbol )
A B C
Atomic
number
3 6 9
Write the symbol of the element which belongs to :( a) group 1 (b) group 14
of the periodic table. State the period of the periodic table to which these
elements belong. State reasonto support your answer.
a) A belongs to group 1
b) B belongs to group 14
Ans. These elements belong to second period because these elements have two
shells. A has electronic configuration 2, 1 has one valance electron so , belongs
to group 1 . B has electronic configuration 2,4 and has four valence electrons so,
belongs to group 14 and period 2, ‘C’ has electronic configuration 2,7 and has
seven valence electrons . All of them contain two shells and so belong to
second period.
Q8. A. How are the following related?
i. Number of valence electrons ofdifferent elements in the same
group.
ii. Number of shells of elements in the same period
B. How do the following change?
i) Number of shells of elements as we go down a group
ii) Number of valence electrons ofelements on moving from, left to
right in a period.
Ans .
A.i) Different elements in same group have same number of valence
electrons
ii) Number of shells of elements in same period are equal.
B.i) Number of shells of elements goes on increasing down the group
ii)Number of valence electrons of elements goes on increasing on
moving from left to right in a period, e.g. lithium has 1 , beryllium has 2 ,
boronhas 3 , carbon has 4 , nitrogen has 5 , oxygen haws 6 , fluorine
hasw 7 and neon has 8 valence electrons.
9. In the modern periodic table, the element calcium (atomic number = 20)
is surrounded by elements with atomic numbers 12, 19, 21 and 38.
a) Which of these elements have physical and chemicalproperties
resembling those of calcium and why?
b) Give reasons for the following
i. Elements in group have similar chemicalproperties
ii. Elements of group 1 form ions with charge of+1

4. Ans. a) Elements with atomic number 12, 38 resemble calcium in physical and
chemical properties because they have same number of valence electrons and
belong to same group II
Mg (12): 2, 8, 2
Ca (20): 2, 8, 8, 2
Sr (38): 2, 8, 18, 8, 2
b) i. Elements in group have same number of valence electrons and same
valency therefore have similar chemical properties
ii. It is because elements of group I loose 1 electron to acquire +1 charge and
become stable.
10) a) State the modern periodic law for classificationofelements.
b) How many Groups and Periods are there in the modern periodic table ?
c) What are metalloids ?
Ans. a) Properties of elements are the periodic function of their atomic number
b) There are 18 groups and 7 periods in the modern periodic table
c) Elements which have the properties of metal and non-metals.