We have Provided the NCERT/CBSE Solutions chapter-wise for Class 10 Science Chapter 5 Periodic Classification of Elements with Answers by expert subject teacher for latest syllabus and examination. Students can take a free NCERT Solutions of Periodic Classification of Elements. Each question has right answer Solved by Expert Teacher.
CBSE Solutions Class 10 Science Periodic Classification of Elements
Questions
Page No: 81
Q1. 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.
Q2. What were the limitations of Dobereiner’s classification?
Answer:
- Concept of triads could be applied only to a limited number of elements.
- Dobereiner could identify only three triads from the elements known at that time. So this system was not found to be useful.
Q3. What were the limitations of Newlands’ Law of Octaves?
Answer:
- Actually this classification was successful only upto the element calcium. After that, every eighth element did not possess the same properties as by the element lying above it in the same group. For example, the elements cobalt (Co) and nickel (Ni) placed below chlorine had different properties. Same was the case with copper (Cu) placed after potassium in the same group.
- Newland committed another mistake. He placed two elements in the same slot in a particular group. For example, Co and Ni in the first group after chlorine. Similarly, elements cerium (Ce) and lanthanum (La) were placed after yitterium (Y) in the same group. Newland could not offer any explanation for such an arrangement.
- Newland somehow thought that only 56 elements existed in nature and no more elements were likely to be discovered. But this belief ultimately proved to be wrong.
- When noble gas elements were discovered at a later stage, their inclusion in the table disturbed the entire arrangement.
Page No: 85
Q1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, Si, Ba.
Answer: K2O, CO2, Al2O3, SiO2, BaO.
Q2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Answer: Two other elements are scandium (Sc) and germanium (Ge). In their gaps, the elements with names Eka-boron and Eka-silicon were placed.
Q3. What were the criteria used by Mendeleev in creating his Periodic Table?
Answer: Mendeleev concentrated on various compounds formed by the elements with Hydrogen and Oxygen. Among physical properties, he observed the relationship between the atomic masses of various elements while creating his periodic table.
Q4. 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
Q1. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?
Answer: The Modern Periodic Table is based on the atomic number which is more fundamental property of the elements. The Modern Periodic Table rectify the various anomalies of Mendeleev’s Periodic Table; which are given below.
- Since this classification is based on the atomic number, the position of placing isotopes at one place is justified.
- It separate metals and non-metals and metalloids clearly.
- The position of some elements which were misfit on the basis of atomic mass is justified on the basis of atomic no. For example, argon proceeds potassium because argon has atomic number 18 and potassium has 19.
- The lanthanoids and actinoids which have properties different from other groups are placed separately at the bottom of the periodic table.
- It separates very soft elements (Na, K…) from very hard elements (Cu, Ag, Au).
- This periodic table does not has sub-groups but it has only groups starting from 1 to 18.
Q2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Answer: Magnesium (Mg) belongs to group 2 known as Alkaline Earth Family. The two other elements belonging to the same group are calcium (Ca) and strontium (Sr). The basis of choice is the electronic distribution in the valence shell of these elements. All of them have two electrons each.
| K | L | M | N | O | |
| Mg (Z =12) | 2 | 8 | 2 | – | – |
| Ca (Z = 20) | 2 | 8 | 8 | 2 | – |
| Sr (Z = 38) | 2 | 8 | 18 | 8 | 2 |
Q3. 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 : Atomic number – 3(2, 1); Sodium : Atomic number – 11(2, 8, 1); Potassium : Atomic number – 19(2, 8, 8, 1).
(b) Beryllium : Atomic number – 4(2, 2); Calcium : Atomic number – 20(2, 8, 8, 2)
(c) Helium : Atomic number – 2(2); Neon : Atomic number – 10(2, 8); Argon : Atomic number – 18(2, 8, 8).
Q4. (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?
Answer: They’ve one valence electron in their outermost shells and as a result of this, they are very unstable. So, they readily react with water to liberate hydrogen. They are also called alkali metals.
(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: Their outermost shells are full leading to high stability. They react only in extreme circumstances and hence are called noble gases.
Q5. In the Modern Periodic Table, which are the metals among the first ten elements?
Answer: Metals among the first ten elements are lithium (Li) and beryllium (Be). These are placed towards the left of the table.
Q6. 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.
Excercise
Q1. 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.
Answer: (c) The atoms lose their electrons more easily.
Q2. 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
(c) Al
(d) Si
Answer: (b) Mg
Q3. 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
Q4. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
Answer: Boron belongs to group no. 13 of the modern periodic table. All the elements of this group has similar valency as boron has. The valency of Boron in Z, because it has three electrons in its valency shell. So all the elements of G-13 have three valency.
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer: Valency of all the elements of the same group will be same. So all the elements of this group shows one valence like fluorine.
Q5. 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 the element is 17 (2 + 8 + 7 = 17).
(b) It would be chemically similar with fluorine (F) which has also 7 electrons in valence shell (2, 7)
Q6. The position of three elements A, B and C in the Periodic Table are shown below –
| Group 16 | Group 17 |
| – | – |
| – | A |
| – | – |
| B | C |
(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) Since the valency of group 17 elements is 1 and all these elements accept electrons, thus A is a non-metal.
(b) C is less reactive than A because as we move down in a group, the reactivity of non-metals increases.
(c) C is smaller in size than B because B and C both are related to the same period and the size decreases as one moves from left to right in a period.
(d) A will form anion because it is a non-metal.
Q7. 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: The electronic configurations of the two elements are nitrogen (Z = 7) 2, 5; Phosphorus (Z = 15) 2,8, 5.
Since the size of nitrogen is small as compared to phosphorus, it has a greater tendency to take up electrons. It is therefore, more electro-negative than phosphorus.
Q8. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer: The number of valence electrons decides an atom’s position in the periodic table while the electronic configuration decides the number of valence electrons.
Q9. 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).
Q10. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.
Answer: Contrast in Mendeleev’s and Modem Periodic Table.
| Mendeleev’s Periodic table | Periodic Table |
| 1. It is based on atomic mass of the elements. 2. It has eight groups. 3. The position of the hydrogen is not justified. 4. There are subgroups (a and b) in each group. 5. This is quite difficult to reproduce. 6. No separate position is allotted to the Lanthanoides and actinoides. | 1. It is based on atomic numbers of the elements. 2. It has 18 groups. 3. The position of hydrogen has been justified. 4. Groups are not further subdivided into subgroups. 5. This is simple and easy to reproduce. 6. Lanthaniods and actinoids are kept in two separate rows and 7. placed under the periodic table. |
We Think the given NCERT Solutions for class 10 Science Chapter 5 Periodic Classification of Elements with Answers Pdf free download will assist you. If you’ve got any queries regarding CBSE Class 10 Science Periodic Classification of Elements NCERT Solutions with Answers, drop a comment below and that we will come back to you soons.