Chapter 3, Problem 1RQ

What did each of the following scientists contribute to our knowledge of the atom?
a. William Crookes
b. Eugen Goldstein
c. Michael Faraday
d. J.J.Thomson
e. Ernest Rutherford
f. James Chadwick

Interpretation Introduction

Interpretation:

Contribution of William Crookes to our knowledge of atom must be stated.

Concept Introduction:

An atom is smallest constituent unit of any kind of matter. It determines the properties of all kinds of matter.

It is made up of three kinds of sub-atomic particles: Protons, neutrons and electrons.

Protons and neutrons are heavier than electrons. They are present in the centre of the atom inside the nucleus. Protons and neutrons both have nearly same mass. Protons are positively charged particles while neutrons are neutral that is they posses no charge.

Negatively charged electrons are orbiting around the nucleus.

Answer to Problem 1RQ

Solution:

William Crookes discovered cathode rays.

Explanation of Solution

William Crookes was an English chemist. In 1875, he made a low-pressure gas tube that allows electric current to pass. This tube consists of two metal electrodes and the electric current was passed through one of the electrodes under vacuum atmosphere.

The beam was observed on the sulfide screen present behind the opposite electrode. The electrically charged particles moved from one of the electrodes, which was Cathode and hit the opposite electrode.

The electrode was Cathode and the particles were Cathode rays.

Conclusion

William Crookes discovered cathode rays.

Interpretation Introduction

Interpretation:

Contribution of Eugen Goldstein to our knowledge of atom must be stated.

Concept Introduction:

An atom is smallest constituent unit of any kind of matter. It determines the properties of all kinds of matter.

It is made up of three kinds of sub-atomic particles: Protons, neutrons and electrons.

Protons and neutrons are heavier than electrons. They are present in the centre of the atom inside the nucleus. Protons and neutrons both have nearly same mass. Protons are positively charged particles while neutrons are neutral that is they posses no charge.

Negatively charged electrons are orbiting around the nucleus.

Answer to Problem 1RQ

Solution:

Eugen Goldstein discovered Protons.

Explanation of Solution

Eugen Goldstein was a German scientist who performed experiments with gas discharge tubes containing perforated cathode. He proved that along with the negative charged electrons that are released from cathode, some oppositely charged particles are also released from anode and moved towards cathodes.

Few of these particles passed through holes in cathode and were deflected under magnetic field. These were positively charged protons.

Conclusion

Thus, Eugen Goldstein discovered Protons.

Interpretation Introduction

Interpretation:

Contribution of Michael Faraday to our knowledge of atom must be stated.

Concept Introduction:

An atom is smallest constituent unit of any kind of matter. It determines the properties of all kinds of matter.

It is made up of three kinds of sub-atomic particles: Protons, neutrons and electrons.

Protons and neutrons are heavier than electrons. They are present in the centre of the atom inside the nucleus. Protons and neutrons both have nearly same mass. Protons are positively charged particles while neutrons are neutral that is they posses no charge.

Negatively charged electrons are orbiting around the nucleus.

Answer to Problem 1RQ

Solution:

Michael Faraday established the electrical nature of atoms.

Explanation of Solution

Michael faraday discovered the phenomenon of electromagnetic induction and electrolysis. His contribution to atomic theory is that he discovered that toms are electrical in nature.

He placed two electrodes in a solution of a compound in water. And observed that one of elements in the compound is deposited on one electrode and the other is deposited on the other electrode. He concluded that electric forces are responsible for this deposition.

The two electrodes were oppositely charged. The positive charged electrode was named cathode and negative charged electrode was named anode.

Conclusion

Thus, Michael Faraday established the electrical nature of atoms.

Interpretation Introduction

Interpretation:

Contribution of J. J. Thompson to our knowledge of atom must be stated.

Concept Introduction:

An atom is smallest constituent unit of any kind of matter. It determines the properties of all kinds of matter.

It is made up of three kinds of sub-atomic particles: Protons, neutrons and electrons.

Protons and neutrons are heavier than electrons. They are present in the centre of the atom inside the nucleus. Protons and neutrons both have nearly same mass. Protons are positively charged particles while neutrons are neutral that is they posses no charge.

Negatively charged electrons are orbiting around the nucleus.

Answer to Problem 1RQ

Solution:

J. J. Thompson discovered electrons.

Explanation of Solution

After William Crookes discovered cathode rays there were several speculations about their nature.
Nature of cathode rays was studies by an English physicist J. J. Thompson. He passed cathode rays through an electric field and showed that cathode rays were attracted to positive plate and repelled by the negative plate and hence proved that cathode rays consist of negative charged particles which were named as electrons.

Conclusion

Thus, J. J. Thompson discovered electrons.

Interpretation Introduction

Interpretation:

Contribution of Ernest Rutherford to our knowledge of atom must be stated.

Concept Introduction:

An atom is smallest constituent unit of any kind of matter. It determines the properties of all kinds of matter.

It is made up of three kinds of sub-atomic particles: Protons, neutrons and electrons.

Protons and neutrons are heavier than electrons. They are present in the centre of the atom inside the nucleus. Protons and neutrons both have nearly same mass. Protons are positively charged particles while neutrons are neutral that is they posses no charge.

Negatively charged electrons are orbiting around the nucleus.

Answer to Problem 1RQ

Solution:

Ernest Rutherford discovered nuclear model of atom.

Explanation of Solution

Rutherford did the famous gold foil experiment in which he bombarded a gold foil with alpha particles emitted from a radioactive source.

Most of particles in his experiments passed straight though the foil with little or no deflection. A few particles were deflected sharply, and one was deflected right back.

He concluded that most positive charge in the gold atom is concentrated in the centre which completely deflected back one of the positive alpha particles that might have hit it right at the centre. Other particles that were deflected by an angle might have hit it near to centre. By this he concluded that positive charge at the centre occupies a small volume of the atom. This was named as nucleus which contains all the positive charge.

Most of particles passed straight though the foil proves that is a lot of empty space in an atom. The space around the nucleus contains negatively charged electrons. Due to very little mass of electrons as compared to alpha particles, they did not affect alpha particles.

Conclusion

Thus, Ernest Rutherford discovered nuclear model of atom.

Interpretation Introduction

Interpretation:

Contribution of James Chadwick to our knowledge of atom must be stated.

Concept Introduction:

An atom is smallest constituent unit of any kind of matter. It determines the properties of all kinds of matter.

It is made up of three kinds of sub-atomic particles: Protons, neutrons and electrons.

Protons and neutrons are heavier than electrons. They are present in the centre of the atom inside the nucleus. Protons and neutrons both have nearly same mass. Protons are positively charged particles while neutrons are neutral that is they posses no charge.

Answer to Problem 1RQ

Solution:

James Chadwick discovered Neutrons.

Explanation of Solution

James Chadwick bombarded beryllium atoms with alpha particles. A new type of radiations was observed which was neutral in charge and mass of the particles was same as proton. Chadwick names them as neutrons.

Conclusion

Thus, James Chadwick discovered Neutrons.