## Samacheer Kalvi 9th Term II Science Book Back Question and Answers – Unit 4:

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### Samacheer Kalvi 9th Science Book Back Unit 4 Term 2 Solutions Guide PDF:

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### Periodic classification of elements

1. If Dobereiner is related with ‘law of triads’. Then Newlands is related with
a) Modern periodic law
b) Hund’s rule
c) law of octaves
d) Pauli’s Exclusion principle

2. Modem periodic law states that the physical’ and chemical properties of elements are the periodic
functions of their
a) atomic numbers
b) atomic masses
c) similarities
d) anomalies

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

4. The increasing order of the energy of subshells is
a) s>p>d>f
b) s< p<d<f
c) s<p <f<d
d) p<s<d<f

5. If the electronic configuration of an element is 1s2 2s2 2p6 3s2 3p1 then it will occupy block of the periodic table
a)s
b) p
c) d
d) f

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 18 group of the periodic table.
3. The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was atomic mass
4. B, Si, Ge and As are the examples of metalloids
5. Example for liquid metal is mercury

III. Match the following:

2. Alkali metal                    b) Calcium
3. Law of octaves               c) Henry Moseley
4. Alkaline earth metal    d) Sodium
5. Modern Periodic Law  e) Dobereiner
Ans: 1-e; 2-d; 3-a; 4-b; 5-c

IV. State whether True or False:

1) Newlands’ periodic table is based on atomic masses of elements and modem periodic table is based on
atomic number of elements. – True
2) Metals can gain electrons. – False
3) Alloys bear the characteristics of both metals and nonmetals. – False
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. J –True
5) Group 17 elements are named as Halogens. –True

V. Assertion and Reason:

1. 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.

VI. Arrange the Jumbled letters to answer the following

1. LAOHSENG – We are a family of live and lies in 17th group of periodic table. (7letters)
Ans: HALOGEN
2. SDIMUO – I am being stored in kerosene and be cut by knife
Ans: SODIUM
3. RIDMUII – I am the most corrosion resistant silvery white metal and lies in group 9 (7 letters)
Ans: IRIDIUM
4. TIRNGONE – I am being used as refrigerant in liquid from with atomic number 7. (8letters)
Ans: NITROGEN
5. NROI – I am in your blood as hemoglobin and without me no buildings are possible. (4letters)
Ans: IRON
6. IHNMUINO – I am the highly radioactive and newly designated element in the modern periodic table with atomic number 113. (8 letters)
Ans: NIHONIUM
7. HCLEIRNO – I am used as a disinfectant for drinking water. (8letter)
Ans: CHLORINE
8. ENIDOI – I am mixed with salt and used for thyroid health (6 letters)
Ans: IODINE
9. BARCON – I am the key part of biological molecules and have the valency of four. (5letters)
Ans: CARBON
10. ELIHUM – I am the first in the noble gas group and used to fill balloons.
Ans: HELIUM

1. State Modern Periodic Law.
The Modern Periodic Law can be stated as follows: “The Chemical and Physical properties of elements are periodic functions of their atomic numbers”.

2. What are groups and periods in the modern periodic table?
– The horizontal rows are called periods. There are seven periods in the periodic table.
– The elements are placed in periods based on the number of shells in their atoms.
– Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
– Based on the physical and chemical properties of elements, they are grouped into various families.

3. What are the limitations of Mendeleev’s periodic table?
In the periodic table, Hydrogen is placed at the top of the alkali metals. Alkali metals are solids while hydrogen is a gas.
Hence the position of hydrogen in the modem periodic table is still under debate as the properties of hydrogen are unique.

4. State any five features of modern periodic table.
– The table is based on a more fundamental property i.e., atomic number.
– It correlates the position of the element with its electronic configuration more clearly.
– The completion of each period is more logical, hi a period, as .the atomic number increases, the energy shells are gradually filled up until an inert gas configuration is reached.
– It is easy to remember and reproduce.
– Each group is an independent group and the idea of subgroups has been discarded.