Nuclei

The nucleus is located at the centre of an atom and the whole mass of an atom is concentrated in it. A nucleus is extremely small and is surrounded by lightweight electrons that spin in and around the atom without disturbing the empty space between the boundaries of the nucleus and atoms. Dive into the topic to know more in detail about an atom’s nuclei.

What is a nucleus?

A nucleus is a positively-charged entity situated at the centre of the atom, and electrons that revolve around the nucleus in an orbit are negatively charged.

A nucleus radius is smaller than that of an atomic radius. The atom’s mass is focused on the nucleus. 

An atom has three main components; a neutron (neutral charge), proton (positively charged), and an electron (negatively charged). The mass of a proton and neutron is always the same and both the entities are bonded together with a force called nuclear force. 

Composition of a Nuclei

• The nucleus has two main components: protons and neutrons.

• The positively-charged entities are protons that are solely present inside the nucleus and neutrons are neutral in charge and do not carry any charge.

• Atomic number: –

  • The total number of protons present inside a nucleus of an atom is called atomic number. 

  • The atomic number is denoted by the letter ‘Z’.

• Atomic mass:-

  • The total combined number of neutrons and protons present inside a nucleus is called atomic mass.

  • While calculating the mass of an atom, the mass of electrons should not be calculated; rather only the mass of neutrons and protons are taken into consideration. This is because the electrons are the lightest particles in a nucleus, and hence their mass is never considered while calculating atomic mass. 

  • The atomic mass number is also known as mass number.

  • The atomic mass number is denoted by the letter ‘A’.

• Nucleons  –-> The combination of protons + neutrons is called nucleons. 

Types of Nuclei

1. Isotopes: – Isotopes are a set of any two nuclei that have the same atomic number but a different mass number.

• For example: If there are 3 isotopes of carbon (C) having the same atomic number 6, but different mass numbers, that is, 12,13 and 14 – (12C6), (13C6), (14C6)

2. Isobars: – Isobars are any set of nuclei having the same mass number but different atomic numbers.

For example: The two isobars Nitrogen (14N7) and Carbon (12C6) that have the same mass numbers are 14, but different atomic numbers that are 7 and 6, respectively.

3. Isotones: – Isotones are nuclei that have the same number of neutrons but different atomic numbers.

For example: Boron (125B) and Carbon (136C).

Boron: Atomic number = 5 and mass number =12.

Carbon: Atomic number = 6 and mass number =13.

In the above-mentioned example, you can easily see that the number of neutrons in the atom Boron (12-5 =7) and the atom carbon (13-6 = 7) are the same.

Nuclide: Nuclides are a collection of nuclei having the same atomic number and also the same number of neutrons.

Charge on a Nucleus

• Nucleus as a whole is a positively-charged entity, but its constituents, that is, protons (positively charged) and neutrons are neutral(no charge). The overall charge on the nucleus is due to only protons.

• An atom consists of electrons, protons and neutrons.

• Formula for total charge of an electron:

• For this, consider an element AXZ
  Where Z= atomic number (the number of protons = Z and the number of neutrons = Z), A is the mass number.

• Therefore, the total charge on all the electrons (e) is = (Ze) 

Note: The total charge of the nucleus should be equal and always opposite to that of the charge on the electron, that is, If the atom is electrically neutral, the total charge on the nucleus should be + (Ze). 

Functions of a nucleus

Ernest Rutherford first found the existence of a nucleus in an atom in the year 1920. Later, James Chadwick in 1932 discovered neutrally-charged neutrons. 

Although a nucleus is a very small entity, it has both protons and neutrons in it. Both the protons and neutrons have a very small radius of 10-15m. 

The functions of a nucleus in an atom can be depicted when the atom is heated, as when heated, it tends to radiate visible light. However, the interesting part here is that when the nucleus is heated, it tends to emit gamma rays. These gamma rays are 100,000, or a million times, more energetic than the visible light emitted by an atom as a whole. 

There have been many models till now that try to describe the behaviour of the nucleus particles, however, the shell model is the most successful. The shell model describes the emission of gamma rays through the nucleus when heated, by putting both the protons and neutrons in different energy shells.

Nuclear binding energy

The total energy required to hold the protons and neutrons of an atom together in a nucleus is known as nuclear binding energy.

By holding the neutrons and protons together, the nuclear binding energy always keeps the nucleus intact.

The nuclear binding energy can also be defined as the total energy required to separate the nucleons, that is the protons and neutrons of an atom.

By determining the value of nuclear binding energy, one can determine if the neutrons and the protons are held together tightly or the bond between them is loose. 

It is important to keep in mind that if the value of the nuclear binding energy is high, the nucleus is very stable and the energy needed for their separation will be high too. And if the nuclear binding energy is low, the nucleus is not that stable and, therefore, the energy that will be needed to separate the protons and neutrons will also not be that high.

Radioactivity

This is when the nuclei of certain elements give out radiations of α, β, γ rays, each of which represents helium nuclei, electrons, and electromagnetic radiation, respectively. 

Emitting these radioactive rays means that the nuclei are unstable.

Nuclear fission

Nuclear fission was for the very first time performed by a scientist named Fermi. 

When the heavier nuclei are broken down into lighter nuclei, emitting a large amount of energy, the process is called nuclear fission. 

Nuclear fusion

When two lighter nuclei combine to form a heavier nucleus, releasing a huge amount of energy, the process is known as nuclear fusion. 

It is important to keep in mind that to perform this process of nuclear fusion, a huge amount of energy is required, as lighter nuclei need to have sufficient initial energy, so that they can overcome the Coulomb’s law between the electrical charges that are a potential barrier to the process. Thus, this process is only possible in high temperatures.

Conclusion

The centrally-located entity of an atom first discovered by the renowned scientist Ernest Rutherford is called the nucleus. The nucleus consists of neutrons and protons, and the function of a nucleus plays a big role in radioactive reactive reactions like nuclear fission and nuclear fusion. You can study other similar topics like the nucleus of biology where you will get to learn about the nucleus in plant cells, how things work in nucleus without nuclear membrane and the meaning of nucleus in biology.