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Karnataka State Syllabus Class 8 Science Important Questions Chapter 3 Structure of Atom
Question 1.
What is matter? What are the states in which matter usually exists?
Answer:
Anything that has mass and occupies space is called matter. Matter usually exists in solid, liquid or gaseous states.
Question 2.
Who was the first to suggest that matter is made of very small particles called ‘paramanu’?
Answer:
Indian sage Kanada was the first to suggest that all matter is made of very small particles called ‘paramanu’. Paramanu means the final or the ultimate particle.
Question 3.
What is matter made of?
Answer:
All matter is made of elements, compounds or mixtures. All of these are made of atoms or molecules. However, molecules are made of one or more atoms.
Question 4.
What is an element? Give two examples.
Answer:
Any substance which is made up of only one kind of atoms is called an element. E.g. Iron, sodium, oxygen, bromine, etc.
Question 5.
How many elements are known to exist in nature?
Answer:
There are 90 naturally occurring elements.
Question 6.
Describe a simple activity to show that atoms of different elements behave differently.
Answer:
Take water in two beakers. Drop a piece of iron into one of the beakers and a very small piece of sodium into the other. Iron does not show any visible reaction immediately. However, sodium reacts vigorously with water with a hissing sound. This shows that the atoms of iron are different from the atoms of sodium.
Question 7.
Make a list of elements that you use in day to day life. Write their symbols and uses.
Answer:
Question 8.
Name the scientist who put forward his atomic theory in 1803.
Answer:
John Dalton put forward his atomic theory in 1803.
Question 9.
State the postulates of Dalton’s atomic theory.
Answer:
The postulates of Dalton’s atomic theory are:
- All matter is composed of small, indivisible particles called atoms.
- All atoms of a given element are identical in shape, mass and other properties while atoms of different elements are different.
- Atoms of one element cannot be converted into those of another element.
- Atoms of one element combine with those of others in integral ratio (ratio of small whole numbers) to form compounds.
- Atoms are neither created nor destroyed during chemical reactions. They simply get rearranged to form new compounds.
Question 10.
Explain the importance of Dalton’s atomic theory.
Answer:
Dalton’s atomic theory gave exceptional insight into the inner structure of matter. Many unexplained chemical phenomena were explained by Dalton with his theory. Dalton’s theory quickly became the theoretical foundation in Chemistry. His ideas provided a framework that could be modified and expanded by later scientists. Despite its drawbacks, the essence of Dalton’s theory remains valid. Hence, John Dalton is often considered to be the father of modern atomic theory.
Question 11.
Who discovered electrons?
Answer:
Electrons were discovered by J.J. Thomson and his colleagues.
Question 12.
What is a discharge tube?
Answer:
A closed insulating glass vessel containing a gas at low pressure through which an electric current flows when
Question 13.
Describe the construction of a discharge tube.
Answer:
A simple discharge tube consists of a glass tube about 15 cm long and 3 cm in diameter. The tube is fitted with two metal plates, one at each end. One of these plates acts as cathode (negative electrode) and the other as anode (positive electrode). A side tube is connected to a vacuum pump which can be used to reduce pressure of the gas inside the tube. The tube is sealed at both ends electrodes by connecting them to a high voltage D.C. source.
Question 14.
Describe JJ. Thomson’s experiment using discharge tube that led to the discovery of cathode rays.
Answer:
The experimental arrangement used by J.J. Thomson is shown in the figure. He used a discharge tube filled with a gas. He applied high voltage across the electrodes. He lowered the pressure of the gas inside the tube by working the vacuum pump. When the pressure was substantially lowered, he observed a greenish glow on the glass near the anode. He argued that the glow is due to some invisible rays emitted by the cathode and hence called them as cathode rays.
Question 15.
What are cathode rays?
Answer:
When a high voltage is applied across the electrodes of a discharge tube filled with a gas under low pressure, a stream of negatively charged particles are emitted by the cathode. Such rays emitted by the cathode are called cathode rays.
Question 16.
Describe the experiment of JJ. Thomson which established that the cathode rays have mechanical energy.
Answer:
J J. Thomson kept a paddle wheel i n the path of cathode rays. He observed that the cathode rays could make the paddle wheel rotate. From this he concluded that cathode rays consist of a stream of particles which have kinetic energy.
Question 17.
Describe JJ. Thomson’s experiment on the discovery of electrons.
Answer:
The experimental arrangement used by J.J. Thomson is shown in the figure. He used a discharge tube filled with a gas under low pressure. He applied high voltage across the electrodes and lowered the pressure of the gas inside the tube by working the vacuum pump.
When the pressure was substantially lowered, he observed a greenish glow on the glass near the anode. He argued that the glow is due to some invisible rays emitted by the cathode and hence called them as cathode rays.
J.J. Thomson set up an electric field perpendicular to the path of cathode rays. He observed that the cathode rays moved towards the positive plate. From this, Thomson inferred that cathode rays are made of negatively charged particles. He named these particles electrons.
Question 18.
What is the charge and mass of an electron?
Answer:
The charge on an electron is -1 and its mass is negligible compared to the mass of the atom. It is about 1840 times smaller than the mass of an atom of hydrogen.
Question 19.
List the properties of cathode rays.
Answer:
The properties of cathode rays are as follows:
- Cathode rays cause a greenish glow on a glass surface.
- Cathode rays consist of matter particles, and possess kinetic energy. This is why cathode rays set a paddle wheel into motion when it is placed in their path.
- Cathode rays consist of negatively charged particles. Cathode rays get deflected towards the positively charged plate in an electric field.
- Cathode rays travel in straight lines. That is why, cathode rays cast shadow of any solid object placed in their path. The path cathode rays travel is not affected by the position of the anode.
Question 20.
Which postulate of the Dalton’s atomic theory was proved wrong by the discovery of electrons by J. J. Thomson? Explain.
Answer:
The first postulate of Dalton’s atomic theory was proved wrong by the discovery of electrons. The first postulate said that atom is the smallest indivisible particle of matter. The existence of a particle much smaller than the smallest atom (hydrogen) proved that the first postulate was wrong.
Question 21.
What was the experiment performed by Goldstein in 1886?
Answer:
Goldstein conducted an experiment to show that a positively charged particle exists inside an atom.
Question 22.
Explain Goldstein’s experiment which established the presence of positive charges in an atom.
Answer:
Eugen Goldstein used a perforated cathode and conducted the discharge tube experiment in 1886. He observed that certain rays were travelling in a direction opposite to that of the cathode. He called these rays anode rays. He applied an electric field parallel to the path of anode rays. He observed that the path of the rays deflected towards the cathode. These rays contain positively charged particles and are called positive rays.
Question 23.
Who proposed that atomic nucleus is positively charged?
Answer:
Goldstein proposed that atomic nucleus is positively charged.
Question 24.
How did Goldstein establish that anode rays consist ofpositively charged particles?
Answer:
Goldstein subjected the anode rays to an electric field. He observed that the anode rays bent towards
the negative plate. This established that anode rays are made of positively charged particles.
Question 25.
List the characteristics of anode rays.
Answer:
- Anode rays are emitted from the anode of the discharge tube.
- They travel in the discharge tube opposite to the cathode rays.
- They are made of positively charged particles.
- They get deflected towards the negative plate in electric and magnetic fields. However, the deflection is small compared to that of the cathode rays.
- The deflection of the anode rays depends on the nature of the gas in the discharge tube. Heavier the gas, lower the deflection.
Question 26.
When will the mass of the particles in the anode rays produced in a discharge tube be lightest?
Answer:
The mass of the particles in the anode rays is lightest when hydrogen is taken in the discharge tube.
Question 27.
What is a proton? Who gave it its name? What is the mass and charge of a proton?
Answer:
Proton is a subatomic particle which is identical to the nucleus of hydrogen atom. Rutherford gave proton its name. The mass of a proton is approximately equal to the mass of 1840 electrons. The charge on a proton is +1 unit.
Question 28.
Why is an atom neutral in spite of the presence of charged particles in it?
Answer:
An atom usually contains equal number of protons (positively charged particles) and electrons (negatively charged particles). Since the positive charges and negative charges annul each other, an atom as a whole is electrically neutral.
Question 29.
Explain Rutherford’s gold foil experiment that led to the discovery of the nucleus.
Answer:
Rutherford experimented with a thin gold foil. He directed alpha rays (positively charged particles) towards the foil. He observed during the experiment that most of the alpha rays passed right through without getting deflected. Some of the particles were deflected greatly. Some came back in the same direction. This showed that the atom is made up of mainly empty space except in the middle which has the most mass in the atom.
Question 30.
State the conclusions that emerged from Rutherford’s gold foil experiment.
Answer:
The following conclusions were drawn from Rutherford’s experiment on gold foil:
- Most of the fast moving alpha particles went straight through the gold foil undeflected.
- Some of the alpha particles were deflected through large angles.
- A very small number of alpha particles were deflected back.
Question 31.
Why did most of the alpha particles pass straight through the goldfoil in Rutherford’s experiment?
Answer:
Most of the alpha particles passed through the gold foil because the atom is mostly empty.
Question 32.
What did the deflection of some alpha particles in the gold foil experiment show?
Answer:
The deflection of some of the alpha particles in the gold foil experiment suggested that there must be a centrally located positive charge within an atom. The interaction between alpha particles and the positive charge inside an atom caused the deflection of alpha particles.
Question 33.
Why did a few of the alpha particles passed through the goldfoil deflect through small angles and the others through large angles in the experiment conducted by Rutherford?
Answer:
A few alpha particles, in Rutherford’s gold foil experiment, were deflected slightly showing that they were located far away from the centrally located positive charge. The deflection of a few other alpha particles through larger angles indicated that they were closer to the positive charge present inside the atom.
Question 34.
Why did very few alpha particles rebound from the gold foil in Rutherford’s experiment?
Answer:
Rebounding of a very few alpha particles from the gold foil suggested that there is a very small
region inside the atom where positive charge is present. When an alpha particle was shot in the direction of the nucleus, the rebounding occurred. The rebounding also suggested that the region of the atom where the positive charge is located is heavy.
Question 35.
What did Rutherford’s gold foil experiment establish?
Answer:
Prior to the gold foil experi ment, it was bel ieved that the mass of an atom was spread evenly throughout the atom. Rutherford’s experiment proved that there is instead a small, dense, positively charged central region (nucleus) inside an atom. The experiment also showed that the central dense region is surrounded by mostly empty space and very small negatively charged electrons.
Question 36.
What were the assumptions proposed by Rutherford based on his gold foil experiment?
Answer:
- Positively charged particles of an atom are held together in the central region of the atom. It is called nucleus. It is surrounded by electrons.
- The volume of the nucleus is small when compared to the volume of an atom.
- The mass of an atom is concentrated in the nucleus.
- The nucleus is positively charged which is different in magnitude for different elements.
- In a neutral atom the number of electrons outside the nucleus is equal to the number of positively charged particles in the nucleus.
Question 37.
Describe Rutherford’s model of an atom.
Answer:
According to Rutherford’s atomic model, an atom consists of a central tiny part called the nucleus. Most of the mass of the atom is concentrated in the nucleus itself. The nucleus carries a net positive charge. Thus the nucleus of an atom is massive, tiny and positively charged. The region surrounding the nucleus is largely empty. However, negatively charged electrons of negligible mass surround the nucleus. These electrons move around the nucleus just the way planets do around the sun.
Question 38.
On what basis did Rutherford predict that the nucleus of an atom must contain neutral particles of mass equal to that of a proton?
Answer:
Rutherford observed that the charge on the nucleus was equal to the charge on the protons contained inside it. However, the mass of the nucleus was much larger than the sum of the masses of protons that made it. Hence, protons alone could not account for the mass of the nucleus. In order to account for the mass of the nucleus, Rutherford thought that a kind of neutral particle with mass equal to that of a proton must be present inside the nucleus.
Question 39.
Who discovered neutrons? What is the charge and mass of a neutron?
Answer:
Neutron was discovered by James Chadwick in 1932. It is an electrically neutral particle with one unit of mass.
Question 40.
Name the fundamental particles present in an atom.
Answer:
The fundamental particles present in an atom include protons, electrons and neutrons.
Question 41.
List the three fundamental particles and their properties.
Answer:
The three fundamental particles present in an atom and their properties are given in the table below:
Question 42.
What is meant by mass number of an element?
Answer:
The sum of protons and neutrons present in the nucleus of an atom of an element is called its mass number. If z is the number of protons and n is the number of neutrons present in an atom, then its mass number A is given by A = z + n.
Question 43.
An atom of an element consists of 17 protons, 17 electrons and 18 neutrons. What is the mass number of the element? What is the net charge on the atom?
Answer:
Mass number of an element = No. of protons + No. of neutrons = 17+18 = 35. The atom is electrically neutral as it has equal number of electrons and protons. The net charge on the atom is, therefore, zero.
Question 44.
What were the defects of Rutherford’s model of the atom?
Answer:
Rutherford’s model of atom stated that all the positive charge was concentrated in the nucleus and electrons revolved around it. An electron revolving around the nucleus continuously should lose energy. As a result, it should be gradually pulled towards the nucleus and end up colliding with it. If this should happen then the atom would collapse. Rutherford’s atomic model could not explain the stability of the atom. Therefore, there was a need to make improvements in Rutherford’s model.
Question 45.
State the main points of Bohr’s model of the atom.
Answer:
Niels Bohr, in 1913, presented a model of the atom which was an improvement over Rutherford’s model.
1. In an atom, the electrons revolve around the nucleus in certain definite circular orbits called shells. The first shell from the nucleus is called K shell. The subsequent shells as we move away from the nucleus are L, M, N, O,…. in that order.
2. An electron in each shell is associated with a definite amount of energy. Therefore, these circular orbits are also known as energy levels.
3. The energy of an electron remains constant so long as it revolves in its own shell, that is, an electron cannot absorb or emit energy as long as it remains in the same orbit.
4. An electron in a higher shell has more energy than those near the nucleus.
5. The energy levels are characterized by an integer n, where, n can have values 1,2, 3, 4, ………. The integer n (= 1,2,3…) is called the quantum number of the respective orbit. The orbits are numbered as 1,2, 3, 4,……… etc., starting from the nucleus. Thus, the orbit for which n = 1 is the lowest energy level.
6. The maximum number of electrons that can be present in any given orbit is given by 2n2 where n is the order of the orbit from the nucleus or shell number.
Question 46.
Describe Neils Bohr’s atomic model.
Answer:
The atomic model proposed by Neils Bohr was a modified version of Rutherford’s model of the atom. According to Bohr’s model, an atom consists of a central massive part called the nucleus. The nucleus is made of positively charged protons and electrically neutral particles called neutrons.
The negatively charged particles called electrons revolve around the nucleus only in certain permissible orbits called shells. These shells are named as K-shell, L-shell, M-shell and so on in that order starting from the nucleus.
The number of electrons that can be accommodated in any given orbit is given by 2n2 where n is the order of the orbit starting from the nucleus. In any atom, the number of electrons is equal to the number of protons. Hence, an, atom as a whole is electrically neutral.
Question 47.
What is the highest number of electrons that can be present in K, L, M, N, O shells?
Answer:
Note: There cannot be more than 8 electrons in the outermost orbit of an atom
Question 48.
Element calcium has 20 protons and 20 neutrons in its nucleus. Write its atomic structure as per the model proposed by Neils Bohr.
Answer:
Calcium atom:
The number of electrons in various shells: K-shell:2, L-shell:8, M-shelI:8, N-sheIl:2.
Question 49.
An electron in an atom jumps from energy level 3 to energy level 1. Does this atom release energy or absorb energy due to this transition? Explain.
Answer:
An atom in which an electron moves from energy level 3 to energy level 1 releases energy. This is because an electron in level 3 has higher energy than an electron in level 1. Therefore, the atom releases energy when its electron jumps from energy level 3 (higher energy level) to energy level 1 (lower energy level).
Question 50.
Draw a diagram of chlorine atom showing the distribution of electrons in various shells. [Given: A chlorine atom has 17 protons and 18 neutrons in its atom]
Answer:
Calcium atom:
Electrons in various shells: K-shell:2, L-shell:8, M-shell:7.
Question 51.
A sulphur atom has 16 protons and 16 neutrons in its nucleus. Write the structure of an atom of sulphur.
Answer:
Sulphur atom:
Electrons in various shells: K-shell:2, L-shell:8, M-shell:6.
Question 52.
What is meant by ‘atomic number’ of an element? What is the symbol used to denote it?
Answer:
The number of protons present in the nucleus of an atom of an element is called its atomic number. It is denoted by the symbol Z.
Question 53.
An element ‘X’ has atomic number Z and and mass number A. How do you represent this element?
Answer:
An element ‘X’ with atomic number Z and mass number A is represented as zXA.
Question 54.
The symbol of uranium is U. Its atomic number is 92 and mass number is 235. Write this atom symbolically.
Answer:
Uranium atom (or nucleus) with atomic number 92 and mass number 235 is represented as 92IP5.
Question 55.
Fill in the blanks in the following table:
Answer:
Question 56.
Between atomic number and atomic mass, which is unique to an element? Explain with an example.
Answer:
Atomic number is unique to an element. Each element will have the atomic number (No. of protons) which is unique to that element. For instance, an atom that has 8 protons in it is certainly an atom of oxygen. No other element has atomic number 8.
If an atom has 3 protons, then, we can certainly say that it is an atom of lithium. However, mass number is not unique to an element. Atoms with same atomic number may have different atomic masses. Hence, atomic number is more fundamental to an element than atomic mass.
Question 57.
What are isotopes of an element? Explain with a suitable example.
Answer:
Atoms of the same element having different mass numbers are called isotopes of that element. Hydrogen has three types of atoms: 1H1 (protium/hydrogen), 1H2 (deuterium), 1H3(tritium).
Question 58.
An atom of potassium is represented as 19K40. State
- Mass number of this isotope of potassium,
- Atomic number of potassium, and
- The distribution of electrons in an atom of potassium.
Answer:
- The mass number of the isotope of potassium is 40.
- The atomic number of potassium is 19.
- The distribution of electrons in an atom of potassium is 2, 8, 8, 1.
Question 59.
Write the names, symbols, atomic numbers, mass numbers, the number of protons and the number of neutrons in the three isotopes of hydrogen.
Answer:
The three isotopes of hydrogen are protium (also called hydrogen), deuterium and tritium. Their symbols, atomic numbers, mass numbers, the number of protons and the number of neutrons in these isotopes are given in the table below:
Question 60.
Represent by a diagram the three isotopes of hydrogen.
Answer:
Question 61.
What are the isotopes of an element due to?
Answer:
The isotopes of an element are due to the presence of different number of neutrons in the nucleus of their atoms.
Multiple Choice Questions
Question 1.
Cathode rays consist of
(a) negatively charged radiation
(b) positively charged radiation
(c) negatively charged particles
(d) positively charged particles
Answer:
(c) negatively charged particles
Question 2.
The heaviest fundamental particle is
(a) proton
(b) electron
(c) neutron
(d) hydrogen
Answer:
(d) hydrogen
Question 3.
Anode rays were discovered by
(a) Rutherford
(b) J.J. Thomson
(c) Goldstein
(d) Neils Bohr
Answer:
(c) Goldstein
Question 4.
The deflection of alpha particles in the gold leaf experiment conducted by Rutherford is due to
(a) increase in the speed of alpha particles
(b) force of repulsion due to the presence of positive charges in the atom
(c) force of attraction due to positive charges in the atom
(d) decrease in the speed of alpha particles.
Answer:
(b) force of repulsion due to the presence of positive charges in the atom
Question 5.
The simplest atom that does not contain any neutron in its nucleus is
(a) deuterium
(b) tritium
(c) hydrogen
(d) helium
Answer:
(c) hydrogen
Question 6.
Which of the following is deduced from the Rutherford’s scattering experiment?
(a) There are neutrons inside the nucleus.
(b) a-particles are helium nucleus.
(c) The central region of the atom has a net negative charge
(d) Most of the mass is concentrated at the centre of the atom.
Answer:
(d) Most of the mass is concentrated at the centre of the atom.
Question 7.
The existence of isotopes of an element is due to the change in
(a) atomic number
(b) electron number
(c) neutron number
(d) proton number
Answer:
(c) neutron number
Question 8.
The atomic number is the number of
(a) protons
(b) protons plus neutrons
(c) protons plus electrons
(d) protons, neutrons, and electrons in an atom.
Answer:
(a) protons
Question 9.
Isotopes are
(a) atoms of different elements with different masses
(b) atoms of different elements with the same mass
(c) atoms of the same element with same mass
(d) atoms of the same element with different masses
Answer:
(d) atoms of the same element with different masses
Question 10.
Rutherford’s alpha particle scattering experiment established that
(a) protons are not evenly distributed throughout an atom.
(b) electrons have a negative charge.
(c) electrons have a positive charge.
(d) atoms are made of protons, neutrons, and electrons.
Answer:
(a) protons are not evenly distributed throughout an atom.
Question 11.
The particle of an atom which can be removed easily by high energy is
(a) neutron
(b) proton
(c) nucleus
(d) electron
Answer:
(d) electron
Question 12.
Which of the following contain the same type of atoms?
(a) water
(b) salt
(c) sugar
(d) silver
Answer:
(d) silver
Question 13.
Atoms are indivisible according to Dalton. But, the following experiment proved that it is not correct.
(a) cathode ray tube experiment
(b) electrolysis of water
(c) melting of ice
(d) decomposition of potassium
Answer:
(a) cathode ray tube experiment
Question 14.
Atoms of the same element are alike in mass, but this postulate of Dalton is not correct due to,
(a) scattering of alpha particles
(b) isotopes
(c) cathode ray tube experiment
(d) atomic number
Answer:
(b) isotopes
Question 15.
The statement of Dalton which is valid even today is,
(a) atoms of the same element are alike in mass.
(b) atoms of one element cannot be converted into atoms of other element.
(c) atoms can neither be created nor destroyed.
(d) atoms are indivisible.
Answer:
(c) atoms can neither be created nor destroyed.
Question 16.
A student accidentally takes a magnet near T.V. screen and finds that the picture in T.V. gets distorted. Presuming that T.V. works on cathode rays, the reason you can give for this observation is,
(a) cathode rays are charged particles and get deflected by magnet
(b) magnet increases the number of cathode particles
(c) magnet decreases the number of cathode particles
(d) magnetic field interacts with the metallic parts of the T.V. tube
Answer:
(a) cathode rays are charged particles and get deflected by magnet
Question 17.
The number of neutrons present in 92U235 atom is
(a) 92
(b) 235
(c) 143
(d) 327
Answer:
(c) 143
Question 18.
Atomic number of mercury is 80 and that of gold is 79. If a scientist succeeds in removing one proton from an atom of mercury, then the product he can get is,
(a) positively charged gold
(b) positively charged mercury
(c) gold atom
(d) mercury atom with decreased mass
Answer:
(c) gold atom
Question 19.
The experiment of scattering of alpha particles reveals that, atom contains
(a) negatively charged electrons
(b) positively charged nucleus
(c) neutrons which are electrically neutral
(d) electrons revolving around the nucleus
Answer:
(b) positively charged nucleus
Question 20.
The maximum number of electrons that can be present in the fourth shell of an atom is,
(a) 32
(b) 8
(c) 16
(d) 18
Answer:
(a) 32
Fill In The Blanks
1. The total number of protons and neutrons in the nucleus of an atom is called its mass number
2. Almost all the mass of an atom is concentrated in a small region of space called the nucleus
3. The particle in an atom which is electrically neutral is neutron
4. Atoms having same number of protons and different number of neutrons are called isotopes
5. The metal used by Rutherford for his experiment on the scattering of alpha particles is gold
6. The isotope of hydrogen that has two neutrons in its nucleus is tritium
7. The maximum number of electrons that can be accommodated in K-shell is two
8. A substance made of only one kind of atoms is known as element
9. Positive electrode in a discharge tube is also called anode
10. The fundamental particle absent in an atom of hydrogen is neutron
11. The mass number of an atom is 23 and its atomic number is 11. The number of neutrons in the atom is twelve
12. The charge on the particles that constitute cathode rays is negative
13. James Chadwick discovered the particle neutrons
14. The experiment of scattering of alpha particles was conducted by the scientist Rutherford
15. If ‘n’ is the shell number of an atom, then the maximum electrons present in that shell is 2n2
16. The number of neutrons present in the atom 11Na23 is 12
17. The fundamental particle of an atom with negligible mass is electron
18. Presence of negatively charged particles in an atom is proved by the experiment cathode ray tube experiment
19. The name of the element which has the simplest atoms is hydrogen
20. The number of electrons present in the outermost shell of an atom with atomic number 12 is eight
21. Atomic number of an element is 18. The number of protons present in an atom of that element is 18
22. Atoms of the same element with different atomic masses are called isotopes
Match The Following
Question 1.
| A | B |
| 1. Goldstein | a. Discovered electrons |
| 2. Dalton | b. Discovered anode rays |
| 3. Bohr | c. Discovered neutrons |
| 4. Chadwick | d. First to develop an atomic theory |
| 5. JJ. Thomson | e. Discovered the nucleus |
| 6. Rutherford | f. Discovered isotopes of oxygen |
| g. Proposed energy levels in an atom |
Answer:
1 – b, 2 – d, 3 – g, 4 – c, 5 – a, 6 – e.
Question 2.
| A | B |
| 1. Proton | a. Negligible mass |
| 2. L-shell | b. 32 electrons |
| 3. Electrons | c. Dalton’s atomic theory |
| 4. Neutrons | d. 8 electrons |
| e. Electrically neutral | |
| f. Positively charged |
Answer:
1 – f, 2 – d, 3 – a, 4 – e.