NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements
In this page, we have provided Chapter 5 Periodic Classification of Elements NCERT Solutions for Class 10 Science which will make you understand the concepts in better manner and providing in depth analysis of the topics. Chapter 5 Class 10 Science NCERT questions and answers contains topics like Dobereiner’s Triads, Newland’s law of octaves, Mendeleev’s periodic table, Modern Periodic table which will develop your understanding.
Class 10 Science NCERT Solutions will help you in analyzing the problems and can be used to recall various questions any time. These NCERT Solutions are curated by Studyrankers experts in a comprehensive which can be helpful in clearing your doubts instantly.
| Study Reference for Class 10 Chapter 5 Periodic Classification of Elements |
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Page No: 81
1. Did Dobereiner's triads also exist in the columns of Newlands' Octaves? Compare and find out.
Answer
Yes, Dobereiner's triads also exist in the columns of Newlands' Octaves. One such column is Li, K, Na.
2. What were the limitations of Dobereiner's classification?
Answer
Limitation of Dobereiner's classification:
All known elements could not be classified into groups of triads on the basis of their properties.
3. What were the limitations of Newlands' Law of Octaves?
Answer
Limitations of Newlands' law of octaves:
→ It was not applicable throughout the arrangements. It was applicable up to calcium only. The properties of the elements listed after calcium showed no resemblance to the properties of the elements above them.
→ Those elements that were discovered after Newlands' octaves did not follow the law of octaves.
→ The position of cobalt and nickel in the group of the elements (F, Cl) of different properties could not be explained.
→ Placing of iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.
Page No: 85
1. Use Mendeleev's Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, Si, Ba.
Answer
K is in group 1. Therefore, the oxide will be K2O.
C is in group 4. Therefore, the oxide will be CO2.
Al is in group 3. Therefore, the oxide will be Al2O3.
Si is in group 4. Therefore, the oxide will be SiO2.
Ba is in group 2. Therefore, the oxide will be BaO.
2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Answer
Scandium and germanium.
3. What were the criteria used by Mendeleev in creating his Periodic Table?
Answer
Mendeleev used atomic mass of the elements as the unique criteria of the elements. He proposed that the chemical properties of elements are the periodic function of their atomic masses. And thus, he arranged the elements in the increasing order of their atomic masses.
4. Why do you think the noble gases are placed in a separate group?
Answer
Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separate group.
Page No: 90
1. How could the Modern Periodic Table remove various anomalies of Mendeleev's Periodic Table?
Answer
Various anomalies of Mendeleev’s Periodic Table removed as follows in the Modern Periodic Table:
→ Elements are arranged in the increasing order of their atomic number in Modern Periodic Table, thus there was no need for keeping more than one element in one slot.
→ In Modern Periodic Table there was no problem of the place of isotopes, as isotopes have same atomic mass with different atomic numbers.
→ Elements having same valence electron are kept in same group.
→ Elements having same number of shells were put under the same period.→ Position of hydrogen became clarified in as it is kept in the group with the elements of same valence electrons.
2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Answer
Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons (2) is same in all these three elements and since chemical properties are due to valence electrons, they show same chemical reactions.
3. Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.
Answer
(a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.
4. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?
Answer
(a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.
(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.
5. In the Modern Periodic Table, which are the metals among the first ten elements?
Answer
6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?
Answer
Since Be lies to the extreme left hand side of the periodic table, Be is the most metallic among the given elements.
Page No: 91
Excercise
1. Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic Table.
(a) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
► (c) The atoms lose their electrons more easily.
2. Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the Periodic Table as
(a) Na
(b) Mg
► (b) Mg
(c) Al
(d) Si
3. Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 2, 8, 2?
(c) a total of three shells, with four electrons in its valence shell?
(d) a total of two shells, with three electrons in its valence shell?
(e) twice as many electrons in its second shell as in its first shell?
Answer
(a) Neon
(b) Magnesium
(c) Silicon
(d) Boron
(e) Carbon
4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer
(a) Valency equal to 3.
(b) Valency equal to 1.
5. An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.)
N(7) F(9) P(15) Ar(18)
Answer
(a) The atomic number of this element is 17.
(b) It would be chemically similar to F(9) with configuration as 2, 7.
Page No: 92
6. The position of three elements A, B and C in the Periodic Table are shown below -
Group 16
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Group 17
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−
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−
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A
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−
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−
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B
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C
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(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
Answer
(a) A is a non-metal.
(b) C is less reactive than A, as reactivity decreases down the group in halogens.
(c) C will be smaller in size than B as moving across a period, the nuclear charge increases and therefore, electrons come closer to the nucleus.
(d) A will form an anion as it accepts an electron to complete its octet.
7. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Answer
Nitrogen (7): 2, 5
Phosphorus (15): 2, 8, 5
Since, electronegativity decreases with moving from top to bottom in a group, thus Nitrogen will be more electronegative.8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer
In the modern periodic table, atoms with similar electronic configurations are placed in the same column. In a group, the number of valence electrons remains the same.
Elements across a period show an increase in the number of valence electrons.
9. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical properties resembling calcium?
Answer
The element with atomic number 12 has same chemical properties as that of calcium. This is because both of them have same number of valence electrons (2).
10. Compare and contrast the arrangement of elements in Mendeleev's Periodic Table and the Modern Periodic Table.
Answer
| Mendeleev's periodic table | Modern periodic table |
| Elements are arranged in the increasing order of their atomic masses. | Elements are arranged in the increasing order of their atomic numbers. |
| There are 8 Groups. | There are 18 Groups. |
| Each group are subdivided into subgroup 'a' and 'b' |
Groups are not subdivided into sub-groups.
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Groups for Noble gas was not present as noble gases were not discovered by that time.
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A separate group is meant for noble gases.
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There was no place for isotopes.
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This problem has been rectified as slots are determined according to atomic number.
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Go Back To NCERT Solutions for Class 10 Science
Chapter 5 Periodic Classification of Elements Class 10 NCERT Solutions
NCERT Solutions for Class 10 Science will prepare students to do better during immense pressure and at the same time make them fresh and enhances memory. It help students cope with the pressure of the large board examination syllabus. Chapter 5 of NCERT Solutions Class 10 Science consists of 10 questions and 3 in-text questions pages.
Topics in the Chapter
• Making Order Out of Chaos – Early Attempts At the Classification of Elements
→ Döbereiner’s Triads
→ Newlands’ Law of Octaves
• Making Order Out of Chaos – Mendeleev’s Periodic Table
→ Achievements of Mendeléev’s Periodic Table
→ Limitations of Mendeléev’s Classification
• Making Order Out of Chaos – The Modern Periodic Table
→ Position of Elements in the Modern Periodic Table
→ Trends in the Modern Periodic Table
NCERT Solutions for Class 10 Science Chapters:
FAQ on Chapter 5 Periodic Classification of Elements
Is Chapter 5 Periodic Classification of Elements NCERT Solutions really helpful?
Chapter 5 Class 10 Science NCERT Solutions will prepare students to do better during immense pressure. It will help in building a great foundation of concepts and make easy for the students to understand basics. These NCERT Solutions are prepared as per the accordance of latest CBSE guidelines so you can score maximum marks.
What is achievement of Dobereiner’s law of triads?
What are demerits of Newland’s classification?
• This classification failed when the heavier elements beyond Ca were arranged according to Newland’s law of octaves.
• At the time of this law, noble gases were unknown. When noble gases were discovered, neon (Ne) between F and Na, and argon (Ar) between Cl and K, it becomes the ninth element and not the eighth which has the similar properties.
Why did Mendeleev leave some gaps in his Periodic Table?
Mendeleev left some gaps in his Periodic Table for the elements yet to be discovered. He even predicted the properties of these elements by studying the properties of the neighbouring elements.
How does the metallic character change along the period?
As we go from left to right in a period, the metallic character decreases, because of the addition of an electron in the same energy shell each time. So, attraction between the nucleus and the electrons in the outermost shell increases. Thus, tendency to lose an electron decreases and metallic character decreases.