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Atomic Theory - Physics

The word ‘atom’ means ‘invisible’, which comes from a Greek word, atomos. It was first used in the 19th century by chemists to describe chemical elements which cannot be reduced or divided any further. According to the current research, based on the theoretical model of the atom, it can be defined as a dense nucleus surrounded by a cloud of electrons.

An atom is considered the smallest piece of any element which can maintain the properties of the element.

The first person to discover the atom was John Dalton. He was well-versed in meteorology, chemistry, and physics. Dalton is famous for suggesting the atom theory in physics. He is considered the creator of the proposal of the atomic theory. A basic concept used in this theory is the law of conservation of mass and the law of constant composition

The law of conservation of mass states that the total mass which is available before the chemical reaction is the same as the total mass available after the chemical reaction. Simply, one can say this theory as “mass is conserved”. This law was first introduced by Antoine Lavoisier back in the 18th century.

You may also want to learn about atomic number and mass number.

Atomic theory talks about various elementary states and properties which can include both axioms and postulates about atoms. Dalton says that the atomic model present inside the atom is in hard spheres. Meanwhile, Rutherford states that the atomic models contain atoms that can be visualized as solar systems.

Following are the three vital properties that help form the modern atomic theory:

  • All matters that are contained in the particle are produced from the atoms.
  • It is a common fact that different atoms have different elements, whereas the same atoms have the same elements.
  • Atoms are considered as the combination of whole numbers and the ratio which helps them combine to create the compound.

Atoms contain smaller particles inside them which are termed sub-atomic particles. Electrons are determined as small subatomic particles that are present in the outermost layers of an atom. They contain a negative charge. Protons are nothing but other subatomic particles which have positive charges and are present inside the electron layers. They can be quite close to the nucleus and are denoted by P+. Meanwhile, a neutron is another type of subatomic particle which is contained inside an atom. They have the same mass as protons but have no charge. Neutrons can either be represented as n0 or just n. Therefore, an atom comprises both protons and neutrons in its center, whereas electrons on the outer orbits.

The following is a formula to determine the mass number of elements:

Mass number of elements = Number of protons + Number of neutrons

Story of Atomic Theory

Atomic theory is nothing but a scientific theory that describes an atom’s nature and behaviors under different conditions. Matter can be composed of separate units named atoms. Following are the number of theories provided by different scientists:

  • Dalton’s theory
  • JJ Thomson’s theory
  • Bohr’s theory
  • Rutherford’s hypothesis
  • Quark theory
  • Einstein, Heisenberg, and quantum mechanics

According to the atomic theory, this entire universe comprises tiny particles which are surrounded by space. They may vary in size and shape, but they are all small. These tiny particles are termed atoms.

Dalton, in his atomic theory, describes that every element in space can be composed of tiny particles which are invisible to the naked eye. We cannot divide these particles into further elements.

Atoms can neither be created nor be destroyed by living beings

The above statement is a scientifically proven fact. Almost all the elements of atoms might be similar in mass and behavior with very slight or negligible variations.

Because of some flaws in Dalton’s theory, Aristotle opposed and disagreed with the entire theory and proposed his theory, which was then accepted by the whole science community. However, later that incident, a new advancement in atomic theory has been discovered with the help of JJ Thomson in 1897. His theory stated that atoms are not just particles that contain various shapes and structures but they do have a separate shape which is spherical. He also insisted that atoms are tightly and uniformly packed particles. His discovery won the reputed Nobel Prize.

But after some years, a new scientist named Rutherford suggested a new theory that describes that an atom can dwell in empty spaces. He also said that the atoms can only contain few electrons meanwhile the mass was solely concentrated in the center. The center of an atom is the nucleus. Even this discovery was not a complete theory. So, after some years, another scientist, Niels Bohr tried to expand Rutherford’s nuclear model. He convinced the science world that electrons can jump from one orbit level to another. But the major limitation is that it cannot be contained in space. So, they ruled this theory out which made way to a new researcher, Werner Heisenberg. He concluded in his theory that it is nearly impossible to precisely calculate the position and speed of the atom because they move in a quick manner. This has become one of the best discoveries of modern science.

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