[Chemistry Class Notes] on Discovery of Proton Pdf for Exam

An atom consists of three subatomic particles which are – Protons, Neutrons and Electrons. Protons and neutrons are found in the nucleus of the atom while electrons are found in the orbits around the nucleus. In this article, we will discuss the discovery of protons in detail but before that you need to know what protons and their fundamental properties are. 

 

What are Protons? 

Protons are positively charged fundamental subatomic particles of atoms. Its symbol is p or p+. As we know that a hydrogen atom consists of one proton and one electron, so on removing the electron from the hydrogen atom a proton is produced. That is why protons are also denoted as H+. It possesses +1e (or 1.60 x 10-19 coulomb) positive electric charge. Thus, protons have equal and opposite charge of electrons. 

 

The word Proton is a Greek word which means ‘First’. It was 1st used by Ernest Rutherford in 1920. The subatomic particles protons and neutrons are together known as nucleons. Nucleons form the nucleus of an atom.

 

What is The Mass of Proton? 

The mass of the proton is 1.67 x 10-24 gram or 1.67 x 10-27 kg. As we know the mass of an electron is 9.1 x 10-28 so the mass of a proton is 1836 times the mass of an electron. Although the mass of a proton is almost equal to the mass of a neutron. 

 

Discovery of a Proton 

Proton was found at the early stages of the investigations of atomic structure. English chemist William Prout gave Prout’s hypothesis in 1815 in which he proposed that all atoms are composed of hydrogen atoms. He called these hydrogen atoms ‘protyles’. Although it was disproved by various other discoveries and experiments later but set a fundamental base for discovery of various subatomic particles. Then in 1886, German physicist Eugen Goldstein carried out a modified cathode ray tube experiment in which he used electric discharge in a modified discharge tube with perforated cathode. In this experiment he discovered positively charged rays which he named ‘canal rays’. Canal rays are also known as anode rays.

 

Let us investigate the discovery of protons through a detailed explanation of the Canal Ray Experiment performed by Goldstein. 

 

Canal Ray Experiment: Discovery of Protons 

Goldstein used almost the same discharge tube as the cathode ray discharge tube used for discovery of electrons. The point of difference was the perforated cathode used in Goldstein’s canal ray experiment.  

 

Apparatus – Canal ray experiment apparatus consists of a tube (known as anode rays discharge tube) which is made of glass containing two thin pieces of metal, called electrodes, sealed in it. Out of these two electrodes one electrode (or one metal piece) has many holes in it which acts as a cathode while another electrode acts as anode. Both the electrodes are connected to the high voltage generator. The electrical discharge through the gasses could be observed only at very low pressures and at very high voltages. So, the tube was evacuated so that pressure of different gasses could be adjusted. When sufficiently high voltage is applied across the electrodes, current starts flowing through a stream of particles in the tube. 

 

Procedure and Observation – Electric current was passed through both the electrodes which creates an electric field in the tube and ionizes the gaseous atoms in the tube. At this point anode starts emitting positively charged rays which move towards the negatively charged cathode and pass the holes of the cathode and strike the glass walls of the tube at the end near the cathode. These rays produced a faint red glow. These rays were passing in the opposite direction of the cathode rays so it was concluded that the charge they carry must be opposite of cathode rays. As these rays were moving from anode to cathode so called anode rays as well. Due to the same reason the glass tube used in this experiment was called anode ray discharge tube. 

 

The characteristics of positively charged particles of canal rays are listed below –

Thus, Eugen Goldstein 1st observed the protons although it was named and identified in other nuclei by British physicist Ernest Rutherford in 1919. 

 

Properties of Protons

Physical properties of protons are as follows –

• Mass of a Proton – Mass of one proton is equal to that of the mass of one hydrogen atom. As a hydrogen atom contains only one proton in its nucleus and mass of an atom depends on its nucleus. Protons can be produced by removing an electron from a hydrogen atom. The mass of a proton is 1836 times the mass of an electron. Mass of a proton is 1.676 x 10-27 kg or 1.676 x 10-24 g.

• Number of protons in an atom possesses its atomic number. For example, hydrogen contains one proton, so its atomic number is 1 while helium contains two protons, so its atomic number is 2.

 

Fun Facts About Proton

1. Protons live up to 10³⁴ years 

2. Every element or material made in the lab will have at least one proton

3. Protons help bind nuclei together 

Characteristics of Proton

How to Determine the Number of Protons in any Element?

If you want to determine the number of protons, then it is equal to the atomic number of that element. For eg, hydrogen has an atomic number1 hence the number of protons in hydrogen will be 1

Similarly, below is the list of elements with the number of protons in it:

Different Type of Elements and Their Proton Number

Questions that can be asked in the Exam

1. What is the mass of a proton? 

2. How was the proton discovered?

3. Give some properties of proton

4. How many protons do the following elements have?

• Hydrogen

• Oxygen

• Nitrogen

• Potassium

• Magnesium

5. Explain in detail the gold foil experiment with a properly labeled diagram.

6. What color is produced by protons in the cathode ray tube?

7. What is the composition of the proton?

8. Explain some main functions of the proton.

This ends our coverage on the topic “Discovery of a Proton”. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to solve problems based on the topic. If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to website or download Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.