PERIODIC CLASSIFICATION OF ELEMENTS
TEXT BOOK EXERCISES
I. Choose the correct answer :
1. If Dobereiner is related with ‘law of triads’, then Newlands is related with
(a) Modem periodic law
(b) Hund’s rule
(c) Law of octaves
(d) Pauli’s Exclusion principle
[Answer: (c) law of octaves]
2. Modern periodic law states that the physical and chemical properties of elements are the periodic functions of their ――― .
(a) atomic numbers
(b) atomic masses
[Answer: (a) atomic numbers]
3. Elements in the modern periodic table are arranged in ――― groups and ――― periods .
(a) 7, 18
(b) 18, 7
(c) 17, 8
(d) 8, 17
[Answer: (b) 18, 7]
II. Fill in the blanks :
1. In Dobereiner’s triads, the atomic weight of the middle element is the average of the atomic masses of 1st and 3rd elements.
2. Noble gases belong to 18th group of the periodic table.
3. The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was atomic mass.
4. Example for liquid metal is mercury.
III. Match the following :
Triads - Newlands
Alkali metal - Calcium
Law of octaves - Henry Moseley
Alkaline earth metal - Sodium
Modern Periodic Law - Dobereiner
Triads - Dobereiner
Alkali metal - Sodium
Law of octaves - Newlands
Alkaline earth metal - Calcium
Modern Periodic Law - Henry Moseley
IV. State whether true or false. If false, correct the statement:
1. Newlands’ periodic table is based on atomic masses of the elements and modern periodic table is based on atomic number of elements.
2. Metals can gain electrons.
Correct statement: Metals tend to lose electrons.
3. Alloys bear the characteristics of both metals and nonmetals.
Correct statement : Metalloids bear the characteristics of both metals and nonmetals.
4. Lanthanides and actinides are kept at the bottom of the periodic table because they resemble each other but they do not resemble with any other group elements.
5. Group 17 elements are named as Halogens.
V. Assertion and reason type questions :
Statement : Elements in a group generally possess similar properties but elements along a period have different properties.
Reason : The difference in electronic configuration makes the element differ in their chemical properties along a period.
a) Statement is true and reason explains the statement.
b) Statement is false but the reason is correct.
[Answer: (a) Statement is true and reason explains the statement]