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Basic Physics Lesson - 20: Atomic Structure

Umesh is a freelance writer contributing his creative writings on varied subjects in various sites and portals in the internet.



We have got so many things around us which have a shape and size and are made up of different materials. Then there are other entities which we feel but cannot see like the air around us which we breathe and is so important for our lives. All these different materials have different characteristics and properties. Scientists and philosophers always wanted to find an answer to this question as to why there is so much difference in the properties and nature of the materials existing around us. Some of these materials are in solid form, some are in liquid form, while some are in gaseous form. What is the composition of these materials and what are the basic components which are present in them to make them so distinguishable? The answer to this question is not simple and it is not possible to find out that with the naked eyee. So the challenge is to find out the smallest part of the material which can be called the basic unit and then can be differentiated from the other materials.

Anyway, scientific studies and research found out that every material us composed of small molecules which themselves are made of some atoms which were unique but gave rise to different materials depending upon in which way they were combined and formed in that material.

This discovery of molecules and atoms was a great milestone in the development of science as it laid a firm footing of theoretical sciences and paved way for many more related understandings.

In this lesson we will learn in details about the atomic structure which is the key to understand the structure and characteristics of different materials.


Molecules and atoms

Though it is not possible manually to divide an item or material further and further in its parts to reach the molecular or atomic stage but it can be studied and visualised using scientific methods.

Theoretically speaking, if we reduce the size of a material then eventually it will reach a molecular state. Each and every molecule will have the same properties as that of the bulk material. This molecule is further made up of some atoms. There are some materials in which there are no molecules as they are made up of a same types of atoms and these materials are known as elements. For example, Iron, Silver, Carbon, etc are composed of only one type of atoms. Of course, what we are talking of is the pure form of these materials. If there are minor impurities mixed in it then the atoms and molecules belonging to those impurities will also be present there. This understanding helps us in learning about the element and compound. The element will have the same atoms in it while the compound will have some combination of atoms (molecules) in it.

Let us understand it with a simple example. When two atoms of hydrogen (H) combine with one atom of oxygen (O) then the resulting product is water (H2O). Here the end result is that we get one molecule of water. The molecule is so small in size that billions of these molecules will be there in a drop of water. As a molecule is comprised of some atoms it is obvious that the size of the atom is much smaller than the molecule.

What is atom

Once we understand the difference between an element and compound (composite material comprising of different elements) then it is easy to visualise what an atom is. By definition, an atom is the smallest part of the particular element which cannot be subdivided further as it would disintegrate the element and result in the production of fundamental particles (neutron, proton, and electrons) and lose the character of the element. So, an atom can be considered as the basic unit and building block of a particular element. The structure of the atom is the characteristic of an element. Understanding the atomic structure helps in learning various aspects of physical phenomenons associated with atoms.

What is inside of an atom

Every atom consists of two main parts. One is the central part known as the nucleus which contains protons and neutrons and the other is the outer part which is the space for the dwelling of electrons. Protons are positively charged particles, electrons are negatively charged particles, and neutrons are neutral particles. The interesting thing is that nucleus is like the core of the atom and electrons are surrounding it at a distance in different orbits. The atom itself is a very very small sized entity and inside that the distribution of nucleus and electron surrounding it is a very microscopic phenomenon and cannot be visualised by naked eyes but in science, we have to understand the concept based on the scientific principles and experiments and deduce things in that fashion only. One interesting thing in this regard is that the atom is having a very small size and inside that, there are so many elementary particles that are much much smaller than the atom and they all are present there in a proportion giving the element or the material its physical and chemical characters.

The size of the atom

The size of the atoms is in the range of nano meters. One nano meter is 10-9 meters which is a very small size (almost a billionth of a meter). Depending upon whether the atom belongs to a metal or gas molecule and also its position in the periodic table, its atomic radius varies in the range of 0.05 nano meter to 0.35 nano meter. Atom is so small that billions of atoms can sit on the tip of a needle.

Atomic structure

Atomic structure is a very interesting geometry in the sense that around the central nucleus which is a positively charged entity there are so many negatively charged electrons surrounding it and in fact orbiting around the nucleus just as the planets in our solar system are orbiting around the Sun. Another interesting thing is that these electrons are orbiting around the central nucleus in different orbits at different distances from the nucleus. it means that some electrons are near the nucleus while some are slightly far away. Now how does it matter? It matters a lot because the electrons which are near to nucleus are definitely attached with a higher electric force than the electrons which are away from it. This also means that if you want to dislodge the electrons from the atom then you have to give less energy to the outermost electrons to dislodge them and will require a higher amount of energy to dislodge the inner electrons. This concept is very important in Physics because it has been able to explain so many things especially the spectrum of the light coming from the atoms and their frequencies and wavelengths depending on the different electronic orbits.

The above explanation is a very simple way to understand how the electrons are existing around the nucleus. But modern scientists explain it in a different way. They say that electrons are just like a cloud of electrons that are present in a probabilistic way around the nucleus and the change in their distance from the nucleus can give rise or can absorb some energy from the surroundings. They also tell that electrons cannot be existing everywhere around the nucleus and they will be existing in certain quantum states and only those quantum states should be the possible places for the existence of electrons. Modern physics also says that small particles like electrons, photons, gamma-ray etc are having dual nature and they can exist as a particle as well as wave so their behaviour will manifest as per this duality of their nature.

Electrons move from one state to other

The classical Physics theories well explain the emission or absorption of energy by an atom when its electrons move from one orbit to another. Because of discrete orbits in which electrons move the energy packets absorbed or released in the process are also a characteristic of that atom of a particular element and by observing and studying the spectrum of that energy by spectrometers we can find out the existence of a particular element in a sample. These observations have created a new branch of Physics known as spectroscopy which is used for various purposes like the identification of different materials.

What are ions

As we saw the atom consists of a central nucleus surrounded by the outer electrons. Electrons are negatively charged particles. Sometimes the electrons in the outermost orbits get dislodged due to external forces and the atom lacks them and becomes positively charged and this combination of electrons dislodged and the atom becomes positive which helps in the flow of electric current through the material. The positive ions are actually the atoms lacking electrons and their sizes are comparable to the atoms only. The dislodged electrons present in the material are actually negative ions. In presence of external electric field they will start moving and that is what creates an electric current flow in the material.

How atoms are arranged inside an element

When we see material (elements) from outside we cannot comprehend anything about its atomic structure because that is not seen by our eyes. The structure is available at a very microscopic level which only we can find by indirect methods.

In a solid element like metals (as Iron, Aluminium, Gold, Silver etc) the atoms are bound with such a force that the element looks solid from outside. At the same time if the inter-atomic force is not very high then the material might not remain stable and start to flow and behave like a liquid. For example, Mercury (Hg) is such a metal.

The atoms are generally arranged in a solid in some particular fashion which is inherent to it and it is formed in the crystallised state where small crystals of metals are formed. The pattern or design of the atoms inside the element is known as the crystal lattice and is a general term to denote that for all the materials.

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Spectroscopic analysis of materials

Every material is unique in its atomic or molecular structure and spectroscopy is a method by which we get valuable information about it. What we do in the spectroscopic methods (spectrometry) is that we bombard a small sample of the material with electromagnetic radiation. The atoms of the material absorb some energy from this electromagnetic radiation and the electrons utilise this energy to go to the higher energy states. As every material is having different levels of these electron energy states, the absorption of the energy will also be having a different wavelength and by knowing this absorbed wavelength we get the information about the material and the range of absorbed wavelengths are known as the absorption spectrum of the material.

The interesting thing to note is that the electrons which go up to the higher energy states come back to their initial states and while coming back to their initial states they give out some energy depending upon the difference between the two energy states which is again the characteristics of that material. As there are many possible energy states of the electrons within the atom structure it is obvious that we would be observing various energy packets corresponding to different wavelengths coming out of the atom and that is actually the spectra of the emitted electromagnetic energy and is a characteristic of a material. So, if we have an unknown sample we can find about it through this spectroscopic method by analysing its absorption and emission spectrum under the influence of electromagnetic radiation being imparted on it.

Spectroscopy has developed as a full-fledged branch of Physics and it is used for many studies related to the atomic structures of various materials. It is extensively used for finding the atomic and molecular structures of the materials and even the combination of the different materials in a sample.

Spectroscopy is being used in many fields like space exploration, medical field especially protein analysis, the structure of chemicals and drugs, marine life investigations, water analysis especially for dissolved oxygen etc.


A compound is made up of molecules that further consist of atoms. An element is made up of atoms. The structure of the atom is very interesting consisting of a nucleus and the surrounding electrons. The nucleus contains protons and neutrons. The number of these basic (elementary particles) particles that is electron, proton, and neutron are the characteristics of that element and every atom of that particular element will have the same combination.

Protons, Neutrons, and Electrons





This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Umesh Chandra Bhatt


Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on October 22, 2021:

Flourish, thanks for your visit and taking interest in my article. Appreciate much.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on October 22, 2021:

Pamela, thanks for your visit and for the nice comment. Highly appreciate.

FlourishAnyway from USA on October 22, 2021:

I recall learning about this in high school, and it was funny how the teacher spent longer on certain chapters when he preferred the topic. This was one of the them. You review the information succinctly.

Pamela Oglesby from Sunny Florida on October 22, 2021:

This is a good scientific article, Umesh. You explained molecules, elements, etc. very well. You are good at writing a technical article.

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