RBSE Solutions For Class 10 Science Chapter 7: Atomic Theory, Periodic Classification and Properties of Elements | Textbook Important Questions & Answers

Students can refer to these RBSE Class 10 Science Chapter 7 Solutions while solving textbook questions. These solutions give an idea to the students in solving the final question paper. All the questions are solved correctly with suitable diagrams in a simple language. With the help of these solutions, students get to analyze their level of preparation and work on their weak points. These solutions are more effective than any other educational resource. We provide elaborate explanations, detailed solutions, descriptive diagrams and more.

RBSE Class 10 Science Chapter 7 solutions are prepared by subject specialists stressing on the importance of all main concepts. These solutions help the students in learning even a complicated topic with ease, preparing the students well for the upcoming board exams. These RBSE Class 10 solutions enable students to understand all the fundamentals of Science.

RBSE Class 10 Science Chapter 7: Objective Textbook Questions and Solutions

Q1. Which radiation did Rutherford use in his experiment?

(A) α

(B) β

(C) V

(D) X

Answer: A

Q2. Which is the smallest particle of substance?

(A) Molecule

(B) Atom

(C) Element

(D) Compound

Answer: B

Q3. Who gave the first periodic classification of elements?

(A) Dobereiner

(B) Moseley

(C) Newland

(D) Mendeleev

Answer: D

Q4. On which property is the modern periodic table based?

(A) Atomic Structure

(B) Atomic Weight

(C) Atomic number

(D) Valency

Answer: C

Q5. Number of periods and groups in the modern periodic table are

(A) 7 and 18

(B) 9 and 18

(C) 7 and 20

(D) 9 and 20

Answer: A

Q6. In periodic table, on moving down a group, atomic size

(A) Decreases

(B) Remains Constant

(C) Remains Irregular

(D) Increases

Answer: D

Q7. Vanderwaal radius is ………. than covalent radius

(A) Smaller

(B) Larger

(C) Same

(D) None of these

Answer: B

Q8. In short period, number of elements are

(A) 2

(B) 8

(C) 18

(D) 32

Answer: B

Q9. Energy given to isolate electron from neutral atom is:

A) electron gain enthalpy

(B) electronegativity

(C) Ionization enthalpy

(D) excitation energy

Answer: C

Q10. Which element has highest electronegativity?

(A) H

(B) Na

(C) Ca

(D) F

Answer: C

Q11. Members of which groups have highest metallic properties:

(A) 1

(B) 2

(C) 5

(D) 6

Answer: A

RBSE Class 10 Science Chapter 7: Very Short Answer Type Questions and Solutions

Q12. Write the name of Thomson’s model.

Answer: Thomson proposed that the shape of an atom resembles that of a sphere having a radius of the order of 10-10 m. The positively charged particles are uniformly distributed with electrons arranged in such a manner that the atom is electrostatically stable. Thomson’s atomic model was also called the plum pudding model or the watermelon model. The embedded electrons resembled the seed of watermelon while the watermelon’s red mass represented the positive charge distribution. The plum pudding atomic theory assumed that the mass of an atom is uniformly distributed all over the atom.

Also Read: Thomson’s Atomic Model & Its Limitations

Q13. What are Bohr’s orbit called?

Answer: According to Bohr’s theory:

i. The atom consists of a small positively charged nucleus at its centre.

ii. The whole mass of the atom is concentrated at the nucleus and the volume of nucleus is smaller than the volume of the atom by a ratio of about 1:10.

iii. The nucleus contains all the protons and neutrons of the atom.

iv. The electrons of the atom revolve round the nucleus in definite circular paths known as orbits which are designated as K, L, M, N or numbered as n=1,2,3,4 outward from the nucleus.

v. Each orbit is associated with a fixed amount of energy. Therefore, these orbits are also known as energy levels or energy shells.

Also Read: Bohr’s Model of Atom

Q14. What is modern periodic law?

Answer: The modern periodic table is developed after the periodic law and a periodic table given by Mendeleev. In the latter part of the 18th century, Mendeleev made his periodic table. Scientists did not know about the internal structure of the atom back then. The development of various atomic models and advances in quantum theory revealed that the atomic number is the most basic property of a chemical element. This led to the modification of Mendeleev’s periodic law, which is today called as modern periodic law.

Read more about Modern Periodic table and Modern Periodic law.

Q15. Write Mendeleev’s periodic law?

Answer: In Mendeleev’s periodic table, elements were arranged on the basis of the fundamental property, atomic mass, and chemical properties. During Mendeleev’s work, only 63 elements were known. After studying the properties of every element, Mendeleev found that the properties of elements were related to atomic mass in a periodic way. He arranged the elements such that elements with similar properties fell into the same vertical columns of the periodic table.

Among chemical properties, Mendeleev treated formulae of hydrides and oxides as one of the basic criteria for categorization. He took 63 cards and on each card, he wrote the properties of one element. He grouped the elements with similar properties and pinned it on the wall. He observed that elements were arranged in the increasing order of atomic mass and there was the periodic occurrence of elements with similar properties.

According to this observation, he formulated a periodic law which states: “the properties of elements are the periodic function of their atomic masses”

In Mendeleev periodic table, vertical columns in the periodic table and horizontal row in the periodic table were named as groups and period respectively.

Read more about Mendeleev’s periodic table.

Q16. On the basis of which property Mendeleev kept elements in periodic order?

Answer: Mendeleev observed that elements were arranged in the increasing order of atomic mass and there was the periodic occurrence of elements with similar properties.

Q17. What name was given to members of 18th group?

Answer: Members of group 18 in the modern periodic table are known as the noble gases. The members of the group have eight electrons in their outermost orbit (except helium which has two electrons). Thus, they have a stable configuration. Group 18 elements are gases and chemically unreactive, which means they don’t form many compounds. Thus, the elements are known as inert gases. Like the other group elements, noble gas elements also exhibit trends in their physical and chemical properties.

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Q18. What are the other names of d-block and f-block elements?

Answer: D block elements are the elements which can be found from the third group to the twelfth group of the modern periodic table. The valence electrons of these elements fall under the d orbital. D block elements are also referred to as transition elements or transition metals.

F block elements are divided into two series, namely lanthanoids and actinoids. These block of elements are often referred to as inner transition metals because they provide a transition in the 6th and 7th row of the periodic table which separates the s block and the d block elements.

RBSE Class 10 Science Chapter 7: Short Answer Type Questions and Solutions

Q19. Give the position of metals, non-metals and metalloids in the Periodic Table?

Answer: In the Modern Periodic Table the metals are present on the left side whereas the non-metals on the right side and the metals and nonmetals are separated by a zig -zag line of metalloids.

Q20. Explain periodicity in electron gain enthalpy in a group?

Answer: Electron gain enthalpy (ΔegH) is defined as the enthalpy change associated with an isolated gaseous atom (X) when it gains an electron to form its corresponding anion.

In the modern periodic table, on moving from left to right across a period, the atomic size of elements decreases and the effective nuclear charge increases. Thus, the force of attraction between the nucleus and added electron increases. Hence, electron gain enthalpy becomes more negative while moving right across a period.

Read more: Electron Gain Enthalpy Of Elements In Modern Periodic Table

Q21. What do you understand by Vanderwaal radius and Covalent radius?

Answer: In solid state, half of the distance between atoms of two close non bonded molecules of the same substance is called vanderwaal radius.

When two same atoms of an element are covalently bonded, then half of the distance between nuclei of both atoms is called covalent radius.

Q22. Cation is smaller than neutral atom and anion bigger than neutral atom. Why?

Answer: In formation of positive ion (cation), with removal of electron, outermost shell of electron gets completely over and effective nuclear charge on remaining electrons increases. So size of cation is always less than neutral atom.

In formation of anion, number of electrons in outermost shell increases and the value of effective nuclear charge decreases. So size of anion is always larger than size of neutral atom.

Q23. What is the effective nuclear charge? How it changes in a group and a period?

Answer: The nuclear charge is the total charge in the nucleus for all the protons. It has the same value as the number of atoms. When you reach the end of a cycle and go to the start of the next period, the number of atoms and the nuclear charge continues to rise. The term effective nuclear charge should be used in place of nuclear charge. Effective nuclear charge takes into account the behavior of all electrons whether they constitute the valence shell that is present in the inner shells.

Effective nuclear charge increases when we move from left to right across a period. It reduces when we move down a group.

Q24. Valency shows which type of periodic property while going from left to right in a period?

Answer: On moving from left to right in a period, valency increases from 1 to 4 and then reduces to zero. Number of electrons valence increases from 1 to 8 when we move from left to right across a period.

Q25. Write Dalton’s theory of atomic structure?

Answer: Dalton’s atomic theory was a scientific theory on the nature of matter put forward by the English physicist and chemist John Dalton in the year 1808. It stated that all matter was made up of small, indivisible particles known as ‘atoms’. The postulates and limitations of Dalton’s atomic theory are listed below.

Postulates of Dalton’s Atomic Theory

  • All matter is made up of tiny, indivisible particles called atoms.
  • All atoms of a specific element are identical in mass, size, and other properties. However, atoms of different element exhibit different properties and vary in mass and size.
  • Atoms can neither be created nor destroyed. Furthermore, atoms cannot be divided into smaller particles.
  • Atoms of different elements can combine with each other in fixed whole-number ratios in order to form compounds.
  • Atoms can be rearranged, combined, or separated in chemical reactions.

Limitations of Dalton’s Atomic Theory

  • It does not account for subatomic particles: Dalton’s atomic theory stated that atoms were indivisible. However, the discovery of subatomic particles (such as protons, electrons, and neutrons) disproved this postulate.
  • It does not account for isotopes: As per Dalton’s atomic theory, all atoms of an element have identical masses and densities. However, different isotopes of elements have different atomic masses (Example: hydrogen, deuterium, and tritium).
  • It does not account for isobars: This theory states that the masses of the atoms of two different elements must differ. However, it is possible for two different elements to share the same mass number. Such atoms are called isobars (Example: 40Ar and 40Ca).
  • Elements need not combine in simple, whole-number ratios to form compounds: Certain complex organic compounds do not feature simple ratios of constituent atoms. Example: sugar/sucrose (C11H22O11).
  • The theory does not account for allotropes: The differences in the properties of diamond and graphite, both of which contain only carbon, cannot be explained by Dalton’s atomic theory.

Q26. Explain limitations of Newland’s Law of Octaves.

Answer: Limitations of Newland’s Law of Octaves

The key shortcomings of Newland’s law of octaves are listed below.

  • Several elements were fit into the same slots in Newland’s periodic classification. For example, cobalt and nickel were placed in the same slot.
  • Elements with dissimilar properties were grouped together. For example, the halogens were grouped with some metals such as cobalt, nickel, and platinum.
  • Newland’s law of octaves held true only for elements up to calcium. Elements with greater atomic masses could not be accommodated into octaves.
  • The elements that were discovered later could not be fit into the octave pattern. Therefore, this method of classifying elements did not leave any room for the discovery of new elements.

Q27. Define groups and tables?

Answer: In a periodic table, the vertical columns are called groups and the horizontal rows are called periods.

Q28. What is the Rutherford Atomic Model?

Answer: According to atomic model of Rutherford, most of the mass and positive charge of an atom is concentrated at its centre called nucleus. Most of the part of atom is empty when electron revolve around nucleus.

Q29. On what basis Mendeleev’s periodic table was created?

Answer: Mendeleev created an important periodic table which was divided into periods and groups on the basis of increasing order of atomic weight.

Q30. On what properties metallic and non-metallic properties depend on.

Answer: Metallic and non-metallic properties of elements depend on their atomic size and other periodic properties.

Q31. What is Atomic Radius?

Answer: The distance between nucleus and electron present in outermost shell of atom is called atomic radius. It is very small unit. In a period, on moving from left to right, atomic number increases, thus number of proton in nucleus increases, so more nuclear attraction force act on electrons present in outermost shell, so the atomic radius increases.

Q32. Describe Atomic model of Thomson.

Answer: Thomson atomic model was proposed by William Thomson in the year 1900. This model explained the description of an inner structure of the atom theoretically. It was strongly supported by Sir Joseph Thomson, who had discovered the electron earlier.

During cathode ray tube experiment, a negatively charged particle was discovered by J.J. Thomson. This experiment took place in the year 1897. Cathode ray tube is a vacuum tube. The negative particle was called an electron.

Thomson assumed that an electron is two thousand times lighter than a proton and believed that an atom is made up of thousands of electrons. In this atomic structure model, he considered atoms surrounded by a cloud having positive as well as negative charges. The demonstration of the ionization of air by X-ray was also done by him together with Rutherford. They were the first to demonstrate it. Thomson’s model of an atom is similar to a plum pudding.

Q33. What is Atomic Size?

Answer: Atomic size is the distance between the centre of the nucleus of an atom and its outermost shell.

  • Covalent radius is half the internuclear distance between two atoms of the elements held by a single covalent bond.
  • Van der Waals radius is half of the internuclear distance between two nearest atoms belonging to two adjacent molecules in solid-state.
  • Metallic radius is half the internuclear distance between two nearest atoms in the metallic lattices.
  • Atomic size increases as they pass from the top to the bottom of the periodic table.

Q34. Explain the features of the Modern Periodic Table.

Answer: Features of Modern Periodic Table

There are eighteen vertical columns known as groups in the modern periodic table which are arranged from left to right and seven horizontal rows which are known as periods.

Group number Group name Property
Group 1 or IA Alkali metals They form strong alkalis with water
Group 2 or IIA Alkaline earth metals They also form alkalis but weaker than group 1 elements
Group 13 or IIIA Boron family Boron is the first member of this family
Group 14 or IVA Carbon family Carbon is the first member of this property
Group 15 or VA Nitrogen family This group has non-metals and metalloids
Group 16 or VIA Oxygen family They are also known as chalcogens
Group 17 or VIIA Halogen family The elements of this group form salts.
Group 18 Zero group They are noble gases and under normal conditions they are inert.

Q35. Explain the demerits of modern periodic table.

Answer: Position of hydrogen

  • Position for hydrogen that resembles both electropositive alkali metals and electronegative
  • Nonmetallic halogens, but placed along with alkali metals is ambiguous.

Elements of similar properties like Barium & lead and copper & mercury are separated as in Mendeleev’s, periodic table.

RBSE Class 10 Science Chapter 7: Essay Type Questions and Solutions

Q36. List the merits and demerits of Mendeleev’s periodic table?

Answer: The merits and demerits of Mendeleev’s periodic table are as follows:

Merits of Mendeleev Periodic Table

  • Some gaps were left for the elements yet to be discovered. Thus, if a certain new element is discovered, it can be placed in a new group without disturbing any existing group.

Demerits of Mendeleev Periodic Table

  • He was unable to locate hydrogen in the periodic table.
  • Increase in atomic mass was not regular while moving from one element to another. Hence, the number of elements yet to be discovered was not predictable.
  • Later on, isotopes of elements were found which violated Mendeleev’s periodic law.

Q37. How do the following properties of elements show periodicity in periodic table?

(i) Atomic radius

(ii) Ionization therapy

(iii) Electronegativity

Answer i: Atomic radius decreases when we move from left to right across a period. Atomic radius increases when we move down a group.

Answer ii: Enthalpy of ionisation increases across a period and decreases when we move down a group.

Answer iii: Electronegativity increases when we move across a period. It decreases when we move down a group.

Q38. Explain classification of elements by modern periodic table.

Answer: Classification of the Elements in the Periodic Table:

Classification of the elements in the periodic table can be done in four ways on the basis of their electronic configurations:

1. Noble gas elements:

Elements of group 18 of the modern periodic table are considered a noble gas. The electronic configuration of the first element (helium) of this group is 1s2. Rest all the elements (neon, argon, krypton, xenon, and radon) have their outer shell electronic configuration is ns2np6. As the octet of these elements is complete, hence they are highly stable elements.

2. Representative elements:

S-lock and P-block elements come under the category of representative elements. Elements in groups 1 and 2 are known as the s – block elements (elements with 1s2and 2s2 outermost configuration). Group 13-17 are known as the p-block elements (outermost configuration varies from ns2np1 to ns2np5).

3. Transition elements:

Elements which belong to group 3 to 12 and have their outer shell electronic configuration as (n-1)d1-10ns1-2 are referred to as transition elements. These elements are also known as the d-block elements.

4. Inner transition elements:

Lanthanides and actinides series which fall at the bottom of the periodic table come under the category of inner transition elements. In these elements the 4f and 5f orbitals are partially filled, rendering them special properties.

Q39. Describe Rutherford’s gold foil experiment. Also explain result and conclusions of the experiment.

Answer: Rutherford conducted an experiment by bombarding a thin sheet of gold with α-particles and then studied the trajectory of these particles after their interaction with the gold foil.

Gold foil Experiment and conclusions:

Helium Ions (α-particles) from a radioactive material (Radium) is passed through narrow slits to collimate them into straight-line path. Fast moving α-particles are made to hit a thin sheet (foil) of gold metal of about 100nm thickness. A photographic film or a screen coated with fluorescent- zinc sulphide material, is kept around the gold foil. Number and the angle of deflection of the scattered α-particles all around the gold foil, is measured by their interaction, with the film.

From the location and number of α-particles reaching the screen, Rutherford concluded the following:

  • Almost 99% of the α-particles pass through the gold foil without any deflection. So atom must be having a lot of empty space in it.
  • Several α-particles get deflected at angles. α-particles being positive, the deflection can be caused only by the presence of another positively charged particle inside the atom.
  • A few α-particles (one in twenty thousand) do not either go through or get deflected by the atom, rather they bounce back.

A heavy and highly positively charged particle must then have opposed these, few α- particles

in the atom. A higher charge density indicates a smaller size. Rutherford considered this smaller sized positive charged part as a dense core and called it as nucleus. Nucleus contains all the protons present in the atom and hence the mass of the atom.

The observations made by Rutherford led him to conclude that:

  1. A major fraction of the α-particles bombarded towards the gold sheet passed through it without any deflection, and hence most of the space in an atom is empty.
  2. Some of the α-particles were deflected by the gold sheet by very small angles, and hence the positive charge in an atom is not uniformly distributed. The positive charge in an atom is concentrated in a very small volume.
  3. Very few of the α-particles were deflected back, that is only a few α-particles had nearly 180o angle of deflection. So the volume occupied by the positively charged particles in an atom is very small as compared to the total volume of an atom.

Read More: What are the conclusions of the Gold Foil Experiment?

Q40. State the comparison between Modem Periodic Table and Mendeleev’s Periodic Table.


Mendeleev’s periodic table is based on relation of properties of elements, as dependent on the atomic weight of element. But, Modern periodic table considers atomic number as the fundamental property that decides the properties of elements.

Modern periodic table does correct defects of the Mendeleev’s periodic table. For example, in the Mendeleev’s periodic table, in the element pairs, Argon-potassium, cobalt-nickel, tellurium-iodine and thorium and protactinium, elements with higher atomic mass precedes the element with lower atomic weight. Though it is the right places for them but is against the

Mendeleev’s periodic law.

These elements’ atomic number shows the reverse order compared to atomic mass. The supposed to be wrong positions in Mendeleev’s table has the right explanation justifying their positions.

Uneven grouping of elements: In Mendeleev’s periodic table, coinage metals of copper, silver, and gold are grouped together with very active alkali metals. Manganese metal was grouped with halogens in the seventh group. The defects are rectified in the Modern periodic table.

Position of isotopes: Isotopes with higher atomic weights could not be accommodated in Mendeleev’s table. As isotopes have same atomic number with the stale atom they do not need any separate location in the modern periodic table.

No reasons were offered for the triad elements of VIII group. No such special grouping is given in the modern table.

Mendeleev’s periodic table was for the arrangement of sixty-three elements known at that time.

Modern table accommodates all the 118- natural and synthetic elements.

Atomic number is the fundamental property distinguishing each element and hence, a better basic nature to decide the physical and chemical properties of elemental atoms than atomic weights.

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