Discovery of Protons and Neutrons – Experiment, Observation, Properties, Practice Problems and FAQ

The phenomenon of the generation of electricity was discovered way back in 1752. After more than 100 years, the negative charge in atoms was discovered by J.J Thompson in 1897. The models of an atom were evolving but one question was always knocking on the door of every scientist. If an atom has a charge then why don’t we get current when we touch an atom? There must be an equal and opposite charge which neutralises the negative charge. This question led to the discovery of two more subatomic particles that are protons and neutrons.

Let’s get to know about the discovery and characteristics of protons and neutrons in this article.

TABLE OF CONTENTS

• Protons – Discovery
• Protons – Characteristics
• Neutrons – Discovery
• Neutrons – Characteristics
• Practice Problems
• Frequently Asked Questions – FAQ

Protons – Discovery

With a rest mass of 1.67262 1027 kg, or 1,836 times that of an electron, the proton is a stable subatomic particle with a positive charge that is equivalent to one electron's charge.

All atoms, according to the English chemist William Prout, are composed of hydrogen atoms, which led to the discovery of protons in 1815 (which he referred to as protyles). The charge-to-mass ratio of the hydrogen ion was found to be the highest among all gases when Eugen Goldstein, a German physicist, discovered canal rays (positively charged ions formed by gases) in the year 1886. Additionally, it was noted that among all ionised gases, the hydrogen ion had the smallest size.

In his well-known gold foil experiment in 1911, Ernest Rutherford made the discovery of the atom's nucleus. He came to the conclusion that the majority of an atom's volume was empty and that all of the positively charged particles in it were concentrated in a single core. Additionally, he claimed that the total number of electrons surrounding the nucleus that is negatively charged is equal to the total number of positively charged particles that are inside it.

Ernest Rutherford is credited with discovering the proton when he demonstrated in 1917 that all other atoms' nuclei contain protons. Rutherford is credited with the discovery of the atomic nucleus based on the findings of the gold-foil experiment.

• Ernest Rutherford noticed that when an alpha particle beam was fired into the air, his scintillation detectors picked up hydrogen nuclei.

• Rutherford conducted further research and discovered that the nitrogen atoms in the atmosphere were the source of these hydrogen nuclei.

• He then continued to shoot alpha particle beams into pure nitrogen gas and noticed that more hydrogen nuclei were being produced.

• He came to the conclusion that the hydrogen nuclei were a component of all other atoms and that they descended from nitrogen atoms.

• The nuclear reaction is described by the equation,

14N+ 17O+ p

Where = alpha particle which contains two protons and two neutrons

p=proton

• Later, the hydrogen nucleus was given the name "proton" and was acknowledged as one of the atomic nuclei building blocks.

Protons – Characteristics

• The charge on a proton is positive.
• The nucleus contains protons.
• The rest mass of a proton is 1.672621027 kg, i.e., 1,836 times that of an electron.
• One proton has a charge of 1.602 10-19 C.

Neutrons – Discovery

A neutron is one of the subatomic particles that build up atoms. The neutron has no electric charge and has a mass equal to 1.67493 10-27kg, slightly higher than that of the proton (for numerical simplicity we treat the mass of a proton as equal to the mass of a neutron but nearly 1839 times greater than that of the electron).

In 1920, Ernest Rutherford proposed that the capture of an electron by a proton may produce a neutral particle with a mass similar to that of a proton. This hypothesis sparked a search for the particle. Since nearly all experimental methods used at the time monitored charged particles, their electrical neutrality hindered the search. So what prompted Ernest Rutherford to come up with such speculation?

The atomic mass of elements heavier than hydrogen was greater than their atomic number (the number of protons).

James Chadwick (in 1932) performed the beryllium bombardment experiment and postulated that the radiation was made up of neutrons, which are protons-sized particles without an electrical charge. Since neutrons are electrically uncharged and can enter the atomic nucleus undeflected, this discovery gave scientists a new method for causing atomic disintegration. It also inspired a new theory that the atomic nucleus is made up of protons and neutrons.

Process of Discovery of Neutron

• Chadwick bombarded a thin beryllium sheet foil with alpha particles. The beryllium foil released electrically neutral particles with a mass somewhat larger than that of protons.

• Then, these rays passed through a slab of paraffin wax, and due to collision, charged species (protons) were ejected.

• He named these electrically neutral particles ’neutrons’.

${He}_2^4+{Be}_4^9\to {Be}_6^{12}+n_0^1$

Neutrons – Characteristics

• Neutrons do not carry any charge
• The mass of a neutron is approximately the same as that of a proton. A neutron has a relative mass of 1 u and an absolute mass of 1.674927 10-27kg.

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Discovery of Subatomic Particles - Atomic Structure Class 11 Chemistry Concept | NEET 2024 Exam

Practice Problems

1. Find the mass of 1 mole of neutrons.

1. 10.057 10-4 kg
2. 10.057 10-4g
3. 9.65 104g
4. 5.991023 kg

Answer: A

Solution:

1 mol = 6.022 1023particles

Mass of one neutron = 1.67 10-27kg

∴ Mass of one mole of neutrons = 1.67 10-27kg 6.022 1023= 10.057 10-4 kg

So, option A is the correct answer.

2. The charge on one mole of neutrons is:

1. -9.65 104C
2. 0
3. 9.65 104C
4. Can not be determined

Answer: B

Solution:

1 mol = 6.022 1023particles,

Charge of one neutron = 0

∴ Charge of one mole of neutrons = 0 6.022 1023=0

So, option B is the correct answer.

3. The rest mass of a proton is _____ times the mass of an electron.

1. 1386
2. 1836
3. 1638
4. 1368

Answer: B

Solution:

Mass of proton = 1.67262 10-27 kg

Mass of electron= 9.109382 10-31

Ration of mass of a proton to an electron = 1.67262 10-27 9.109382 10-31 =1836

Hence, the rest mass of a proton is 1836 times the mass of an electron.

So, option B is the correct answer.

4. Which of the following scientists successfully proved the existence of proton?

1. Ernest Rutherford
2. Neil Bohr
3. James Chadwick
4. Eugene Goldstein

Answer: A

Solution: Ernest Rutherford is credited for discovering the proton when he demonstrated in 1917 that all atoms have a proton as part of their nucleus. Goldstein undoubtedly contributed to the idea that the proton is a subatomic particle of the atom before Rutherford, but he was unable to provide us with precise information about it.

So, option A is the correct answer.

Frequently Asked Questions – FAQ

1. Do all atoms have neutrons?
Answer: Except for one, all elements' atoms contain neutrons. Neutrons are absent from the tiny nucleus of a typical hydrogen (H) atom. One electron and one proton are all that little atom (the tiniest of all) has.

2. Is the mass of a neutron exactly equal to the mass of a proton?
Answer:  No, the mass of a neutron is slightly greater than the mass of a proton, but for numerical simplicity, we treat the mass of a single proton as equal to the mass of a proton. The mass of a neutron is 1.674927 10-27kg whereas the mass of a proton is 1.67262 1027 kg.

3. What are the applications of neutrons?
Answer: Some of the basic applications of neutrons are:

1. In boron capture therapy and other medical applications, neutrons are highly ionised, penetrating particles. They do, however, activate the chemical and turn it radioactive when consumed.

2. It is significant in nuclear reactions (understanding the neutron’s behaviour, in particular, has aided in the creation of nuclear weapons and reactors).

3. The neutron emitter is used to find light nuclei in the environment, and the neutron activation analysis (NAA) method is used to investigate a basic sample of materials in a nuclear reactor.

4. Which kind of force is holding neutrons and protons together in a nucleus?
Answer: The forces that exist between two or more nucleons are referred to as nuclear forces (also known as nuclear interactions). They bind the nucleons—protons and neutrons collectively—into the atomic nuclei. The stability of the nucleus is brought about by the nuclear force, which is a short-range force.