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Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 12 Periodic Classification of Elements
Samacheer Kalvi 9th Science Periodic Classification of Elements Textbook Exercises
I. Choose the correct answer.
Question 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
Answer:
(c) Law of octaves
Question 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
Answer:
(a) atomic numbers
Question 3.
Elements in the modem 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.
- In Dobereiner’s triads, the atomic weight of the middle element is the ……………….. of the atomic masses of 1st and 3rd elements.
- Noble gases belong to ……………….. group of the periodic table.
- The basis of the classifications proposed by Dobereiner, Newlands, and Mendeleev was…………………..
- An example of liquid metal is …………………..
Answer:
- average
- 18th
- atomic masses
- Mercury
III. Match the following.
| Column – I | Column – II |
| 1. Triads | (a) Newlands |
| 2. Alkali metal | (b) Calcium |
| 3. Law of octaves | (c) Henry Moseley |
| 4. Alkali earth metal | (d) Sodium |
| 5. Modem Periodic Law | (e) Dobereiner |
Answer:
- (e) Dobereiner
- (d) Sodium
- (a) Newlands
- (b) Calcium
- (c) Henry Moseley
IV. State whether True or False.
- Newlands’ periodic table is based on atomic masses of elements and modem periodic table is based on the atomic number of elements – True
- Metals can gain electrons – False.
Correct Statement: Metals tend to lose electrons to attain Noble Gas electron configuration. - Alloys bear the characteristics of both metals and nonmetals – False
Correct Statement: An alloy is a mixture of metals or a mixture of a metal and another element. - Lanthanides and actinides are kept at the bottom of the periodic table because they resemble each other but they do not resemble any other group elements – True
- Group 17 elements are named as Halogens – True
V. Assertion and Reason
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 the 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 Chemical and Physical properties of elements are periodic functions of their atomic number”.
Question 2.
What are groups and periods in the modern periodic table?
Answer:
- The horizontal rows are called periods. There are seven periods in the periodic table.
- Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.
Question 3.
What are the limitations of Mendeleev’s periodic table?
Limitations of Mendeleev’s periodic table:
Answer:
- Elements with large difference 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 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.
Activity
Question 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:
| Set I: | F | Mg | C | 0 | B |
| Set II: | Cl | Ca | Si | s | Al |
Samacheer Kalvi 9th Science Periodic Classification of Elements Additional Questions
I. Short answers questions.
Question 1.
Why did the classification of elements evolve?
Answer:
Scientists found it difficult to organize all that was known about the elements. Therefore they started looking for some pattern in their properties, and the concepts of classification of elements were proposed by various scientists. This led to the evolution of the classification of elements from the early to modem period.
Question 2.
What is a triads group?
Answer:
Johann Wolfgang Dobereiner arranged the elements into groups containing three elements each based on their relative, atomic masses. He called these groups as ‘triads’ also known as Dobereiner’s Triads.
Question 3.
Explain law of octaves.
Answer:
John Newlands arranged 56 known elements in the increasing order of their atomic mass. He observed that 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 and this arrangement was known as “law’ of octaves”.
Question 4.
What is a periodic table?
Answer:
Dmitri Mendeleev proposed the law of periodicity which states that “the physical and chemical properties of elements are the periodic functions of their atomic masses”. He arranged 56 elements known at that time according to his law of periodicity. This was best known as the short form of the periodic table.
Question 5.
What is IUPAC? Where is it located? Give examples of few elements named by IUPAC.
Answer:
IUPAC stands for-The International Union of Pure and Applied Chemistry. It is an international organization that represents Chemists from various countries. IUPAC is registered in Zurich, Switzerland and has its secretariat in the United States.
Question 6.
How are metals classified in the periodic table?
Answer:
Metals occupy a larger area in the periodic table and are categorized as follows –
- Alkali metals eg. – Sodium and Potassium
- Alkaline earth metals eg. – Calcium and Magnesium
- Transition metals eg. – Iron and Nickel
- Other metals eg. – Aluminium and Tin
Question 7.
What are alkali metals?
Answer:
The elements of group 1 (except hydrogen) are metals. They react with water to form solutions that are highly alkaline or basic. Hence they are called alkali metals.
Question 8.
Though they are found rare, they have many uses. Justify this statement.
Answer:
Helium, Neon, Argon, Krypton, Xenon, and Radon are called the Noble or rare gases and are placed in group 18 in the periodic table. They are monoatomic and do not react with other substances easily. Though these gases are chemically inert, they have stable electronic structures which are difficult to change. Their uses are as follows:
- Helium has a very low density and used for filling weather ballon.
- Neon gas is used in discharge lamps.
- Argon is filled in electrical bulbs to prevent evaporation of the filament.
- Radon is a radioactive gas.
II. Long Answers Questions.
Question 1.
Write any five advantages of the modern periodic law.
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 period 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.
- 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.
Question 2.
Explain the limitations of Mendelev’s periodic table and why is the modern periodic table considered an extension of Mendeleev’s periodic table.
Limitations of Mendelev’s periodic table –
(a) Elements with large difference in properties were included in the same group. Eg. Elard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium and potassium
(b) No proper position could be given to the element hydrogen. Non-metallic Hydrogen was placed along with metals like lithium, sodium and potassium.
(c) The increasing order of atomic mass was not strictly followed throughout. Eg. – Co & Ni, te & I.
(d) No place for isotopes in the periodic table.
The modem periodic table is an extension of the original Mendeleev’s periodic table and is known as the long form of periodic table. Mendeleev’s initial table had 63 elements, modem table has 109 elements. It is also known important to note how the modem periodic table is arranged.
Although the columns which reflect a natural order have been retained, the row’s of the modem table show elements in the order of Mendeleev’s columns. In other words the elements of what we now call ‘a period’ were listed vertically by Mendeleev. ‘Groups are now shown vertically in contrast to their horizontal format in Mendeleev’s table.
Question 3.
What are the advantages of alloys?
- Alloys do not get corroded or get corroded to very less extent.
- They are harder and stronger 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 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 lower melting point than each of the metals).
- When metal is alloyed with mercury, it is called amalgam.
Question 4.
Explain the uniqueness of Hydrogen.
Answer:
Hydrogen is the lightest, smallest and first element of the periodic table. Its electronic configuration (Is1) 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 only 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.