Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 12 Periodic Classification of Elements Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Chapter 12 Periodic Classification of Elements

9th Science Guide Periodic Classification of Elements Text Book Back Questions and Answers

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

I. Choose the correct answer :
Question 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

Question 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
(c) similarities
(d) anomalies
Answer:
(a) atomic numbers

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 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

Fill in the blanks:

1. In Dobereiner’s triads, the atomic weight of the middle element is the __________ of the atomic masses of 1 and 3rd elements.
Answer:
average

2. Noble gases belong to ___________ group of the periodic table.
Answer:
18th

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

3. The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was ……………….
Answer:
atomic mass

4. Example for liquid metal is ______________ .
Answer:
mercury

III. Match the following:
Question

Triads Newlands
Alkali metal Calcium
Law of octaves Henry Moseley
Alkaline earth metal Sodium
Modern Periodic Law Dobereiner

Answer:

Triads Dobereiner
Alkali metal Sodium
Law of octaves Newlands
Alkaline earth metal Calcium
Modern Periodic Law Henry Moseley

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

IV. State whether true or false. If false, correct the statement:

Question 1.
Newlands’ periodic table is based on atomic masses of elements and modem periodic table is based on atomic number of elements.
Answer:
True.

Question 2.
Metals can gain electrons.
Answer:
False.
Correct statement: Metals tend to lose electrons.

Question 3.
Alloys bear the characteristics of both metals and nonmetals.
Answer:
False.
Correct statement: Metalloids bear the characteristics of both metals and nonmetals.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 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.
Answer:
True.

Question 5.
Group 17 elements are named as Halogens.
Answer:
True.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

V. Assertion and Reason :

Question
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

VI. Answer the following :

Question 1.
State modern periodic law.
Answer:
The modem periodic law states that:
“The Chemical and Physical properties of elements are periodic functions of their atomic numbers”.

Question 2.
What are groups and periods in the modern periodic table?
Answer:

  •  The horizontal rows in the periodic table are called periods.
  • Vertical columns in the periodic table starting from top to bottom are called groups.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 3.
What are the limitations of Mendeleev’s periodic table?
Answer:

  • Elements with large differences in properties were included in the same group. Eg: Hard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium (Na) and potassium (K).
  • No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), sodium (Na) and potassium (K).
  • The increasing order of atomic mass was not strictly followed throughout. Eg. Co & Ni, Te &I.
  • No place for isotopes in the periodic table.

Question 4.
State any five features of the modern periodic table.
Answer:

  • All the elements are arranged in the increasing order of their atomic number.
  • 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.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Intext Activities

ACTIVITY -1

Find the pair of elements having similar properties by applying Newlands’ law of Octaves
(Example: Mg & Ca):
Set I : F, Mg, C, O,B
Set II: Al, Si, S, Cl, Ca
Answer:

  1. F-Cl
  2. Mg-Ca
  3. C-Si
  4. O-S
  5. B-Al

9th Science Guide Periodic Classification of Elements Additional Important Questions and Answers

Choose the correct answer:

Question 1.
Noble gases are placed in the _______ group in the modern periodic table.
(a) 13th
(b) 18th
(c) 17th
(d) 2nd
Answer:
(b) l8th

Question 2.
Group 16 elements are collectively called as _______ .
(a) chalcogen family
(b) carbon family
(e) halogens
(d) nitrogen family
Answer:
(a) chalcogen family

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 3.
The maximum number of electrons that can be accommodated in s, p ,d, and f subshells are _________ .
(a) 14, 10, 6, 2
(b) 6, 10, 2, 14
(c) 2, 6, 10, 14
(d) 6, 2, 14, 10
Answer:
c) 2, 6, 10, 14

Question 4.
d-block elements are otherwise known as _________ .
(a) transition elements
(b) inner transition elements
(c) halogens
(d) alkali metals
Answer:
(a) transition elements

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 5.
Which block of the periodic table contains metals, non-metals and metalloids?
(a) s
(b) p
(c) d
(d) f
Answer:
(b) p

Question 6.
Which of the following non-metals can form alloys with metals?
(a) Boron
(b) Carbon
(c) Silicon
(d) All the above
Answer:
(d) all the above

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 7.
Which of the following metals have low melting and boiling point?
(a) Sodium :
(b) Potassium
(e) Iroñ
(d) Both a & b
Answer:
(d) Both a & b

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 8.
Which of the following metal (s) do not react with water?
(a) Gold
(b) Silver
(c) Copper
(d) All the above
Answer:
(d) All the above

Question 9.
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
Answer:
(b) p

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

II. Fill in the blanks :

1. ……………… group elements are called alkaline earth metals.
Answer:
Second

2. The elements that follow lanthanum are called ……………..
Answer:
Lanthanides

3. f-block elements are also known as …………………..
Answer:
inner transition elements

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

4. …………… block element is placed at the bottom of the periodic table.
Answer:
f-

5. The mixture of metal with mercury is called …………………..
Answer:
amalgam

6. Elements are placed in periods based on the number of ……………… in their atoms.
Answer:
shells

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

III. Spot the error :

Question 1.
The elements of group 13 are called the carbon family.
Answer:
The elements of group 13 are called boron family
(or)
The elements of group 14 are called the carbon family.

Question 2.
There are 5 periods and 17 groups in the modern periodic table.
Answer:
There are 7 periods and 18 groups in the modem periodic table.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

IV. Pick the odd one out and write the reason:

Question 1.
Copper, brass, gold ornament, bronze.
Answer:
Copper.
Copper is metal whereas the other three are alloys.

Question 2.
Bromine, carbon, hydrogen, aluminium.
Answer:
Aluminium.
Aluminium is metal whereas the other three are non-metals.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

V. To match :

Group in the modern periodic table Families
a) 1 ?
b) ? Transition metals
c) ? Boron family
d) 15 ?
e) 17 ?

Answer:
a) alkali metals
b) 3 to 12
c) 13
d) Nitrogen family
e) halogens

VI. Answer in brief :

Question 1.
What are the s-block elements?
Answer:
Elements whose valence electron is filled in s subshell is known as s-block elements.

Question 2.
What are the p-block elements?
Answer:
The last electron in these elements is filled in p subshells and hence these elements are called p block elements. These elements are in group 13 to 18 in the periodic table.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 3.
What are alloys?
Answer:
Alloys are mixtures of two or more metals and are formed by mixing molten metals thoroughly. Rarely nonmetals are also mixed with metals to produce alloys.

Question 4.
What are metalloids? Give examples.
Answer:
Elements which have the properties of both metals and non-metals are called as metalloids, (eg) Boron, Arsenic.

Question 5.
State Mendeleev’s Law of Periodicity.
Answer:
The physical and chemical properties of elements are the periodic functions of their atomic masses.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 6.
State Newlands’ Law of Octaves.
Answer:
Every eighth element had properties similar to those of the first element like the eighth note in an octave of music is similar to the first.

Question 7.
An element has atomic number 12.
a) Write the electric configuration.
b)To which group and period do it belong.
Answer:
a) K = 2, L = 8, M = 2
b) Group No . 2, Period No. 3

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 8.
Relate the names of the following scientists with the statements given below. (Mendeleev, Newlands, Dobereiner).
a) Arranged elements into groups containing three elements each.
b) Arranged elements in a group of seven with increasing atomic masses and eighth elements with similar properties kept below the first like eight note in an act of music.
c) Arranged elements in the increasing order of atomic mass
Answer:
a) Dobereiner
b) Newlands
c) Mendeleev

Question 9.
Complete the following triads by inserting the missing elements.
a) Cl, ………., I
b) Li, ………, K
c) Ca, …………, Ba
Answer:
a) Br
b) Na
c) Sr

Question 10.
How are elements grouped into various families in the periodic table?
Answer:
Based on the physical and chemical properties of elements, they are grouped into various families.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

VII. To interpret:

Question 1.
Group 1 (except hydrogen) elements are called alkali metals.
Answer:
The elements of group 1 (except hydrogen) are metals. They react with water to form solutions that change the colour of a vegetable dye from red to blue. These solutions are said to be highly alkaline or basic. Hence they are called alkali metals.

Question 2.
d-block elements are called transition elements.
Answer:
d-block elements are found in the centre of the periodic table. Their properties are intermediate to that of s block and p block elements and so they are called transition elements.

Question 3.
Group 3-12 elements in the modern periodic table are called d block elements.
Answer:
The elements of group 3 to 12 have their valence electrons in their outermost d subshells. These elements are called d block elements.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

VIII. Complete the following table :

Question

Symbol Atomic No. Electronic Configuration
1) He 2 ?
2) Ne ? 2,8
3) Ar ? 2, 8,8
4) Na 11 ?

Answer:
1) 2
2) 10
3) 18
4) 2,8,1

IX. Assertion and Reason :

Question 1.
Assertion (A): Group 2 elements in the modem periodic table are called alkaline earth metals.
Reason (R): The oxides of group 2 elements produce alkaline solutions when they are dissolved in water.
(a) A is right R is wrong
(b) R explains A
(c) R does not explain A
(d) R is right A is wrong
Answer:
(b) R explains A

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 2.
(A) : Noble gases are chemically inert in nature.
Reason (R) : Noble gases have stable electronic structures.
(a) Both A & R are right
(b) Both A & R are wrong
(c) A is right R is wrong
(d) A is wrong R is right
Answer:
(a) Both A & R are right]

Question 3.
Assertion (A): Non-metals are electronegative.
Reason (R) : Non-metal losë electrons to form cation.
(a) Both A & R are right
(b) Both A & R are wrong
(c) A is right R is wrong
(d) A is the wrong R is right
Answer:
(c) A is right R is wrong

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

X. Long answer type questions:

Question 1.
List the advantages of alloys.
Answer:

  • Alloys do not get corroded or get corroded to a very less extent.
  • They are harder and str9ner than pure metals (Example: Gold is mixed with copper and it is harder than pure gold)
  • They have less conductance than pure metals (Example: Copper is a good conductor of heat and electricity whereas brass and bronze are not good conductors)
  • Some alloys have lower melting point than pure metals (Example: Solder is an alloy of lead and tin which has a lower melting point thàn each of the metals)
  • When metal is alloyed with mercury, it is called amalgam.

Question 2.
Write the advantages of the Modern Periodic Table.
Answer:

  • 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 peçiod is more logical. In 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.
  • One position for all isotopes of an element is justified since the isotopes have the same atomic number.
  • The position of the eighth group (in Mendeleev’s table) is also justified in this table. All transition elements have been brought in the middle as the properties of transition elements are intermediate between the left portion and right portion elements of the periodic table.
  • The table completely separates metals from nonmetals. The nonmetals are present in the upper right corners of the periodic table.
  • The positions of certain elements which were earlier misfit (interchanged) in Mendeleev’s periodic table are now justified because it is based on an atomic number of the elements.
  • Justification has been offered for placing lanthanides and actinides at the bottom of the periodic table.

 Samacheer Kalvi 9th Science Guide Chapter 12 Periodic Classification of Elements

Question 3.
Explain the position of hydrogen in the periodic table.
Answer:
Hydrogen is the lightest, smallest and first element of the periodic table. Its electronic configuration (1s1) is the simplest of all the elements. It occupies a unique position in the periodic table. It behaves like alkali metals as well as halogens in its properties. In the periodic table, it is placed at the top of the alkali metals.

  • Hydrogen can lose its one electron to form a hydrogen ion (H+) like alkali metals.
  • It can also gain one electron to form the hydride ion (H) like halogens.
  • 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.

Question 4.
List the features of Mendeleev’s Periodic Table.
Answer:
1. It has eight vertical columns called ‘groups’ and seven horizontal rows called ‘period’.

2. Each group has two subgroups ‘A’ and ‘B’. All the elements appearing in a group were found to have similar properties.

3. For the first time,-elements were comprehensively classified in such a way that elements of similar properties were placed in the same group.

4. It was noticed that certain elements could not be placed in their proper groups in this manner. The reason for this was wrongly determined atomic masses, and consequently those wrong atomic masses were corrected. Eg: The atomic mass of beryllium was known to be 14. Mendeleev reassessed it as 9 and assigned beryllium a proper place;

5. Columns were left vacant for elements which were not known at that time and their properties also were predicted. This gave me the motivation to experiment in Chemistry. Eg: Mendeleev gave the names Eka Aluminium and Eka Silicon to those elements which were to be placed below aluminium and silicon respectively in the periodic table and predicted their properties. The discovery of Germanium later on, during his lifetime, proved him correct.

Properties of Germanium:

Property Mendeleev’s prediction (1871) Actual property (1886)
Atomic Mass About 72 72.59
Specific Gravity 5.5 5.47
Colour Dark grey Dark grey
Formula of oxide EsO2 GeO2
Nature of chloride ESCl4 GeCl4