An atom is the basic unit of matter. It makes the chemical element. It is tiny. Its size is 100 picometers. It is made up of a nucleus and one or more electrons revolving around it. The nucleus is composed of several protons and neutrons. These nuclear particles are made up of quarks. Hydrogen is the only element that has no neutron. More than 99.9% of its mass is present in its nucleus. Proton has a positive charge, the electron has a negative charge, and the neutron has no charge.
In an atom, electrons attract the protons by the electromagnetic force. In the nucleus, protons and neutrons are attracted to each other by the nuclear force. This nuclear force is stronger than the electromagnetic force. But if EMF stronger than nuclear force, the nucleus splits. This process is called atomic decay.
13.7 billion years ago, These were generated after the Big Bang. As the universe cooled down, electrons and quarks were formed. Quarks combined to form protons and neutrons. Protons and neutrons merged to form the nucleus. This process took place within the first few minutes of the existence of the universe. After 380,000 years, the universe became cool enough to slow down the electrons. The nucleus took the electrons which started revolving around it. Then it was formed. Hydrogen and helium are the earliest atoms in the universe. These are still the most abundant elements in the universe.
History of atom
The idea ‘matter is made up of atoms’ is ancient. Greek philosophers gave this idea. The Greek philosopher Democritus first presented his atomic theory. This theory begins with a stone. Suppose a stone is cut in half. It will give two halves of the same stone. If the stone is cut continuously, a point is reached when the stone can no longer be cut. Democritus concluded that matter is made up of small indivisible particles. The word atom is derived from the Greek word atomos, meaning indivisible.
In the early 18s, an English school teacher John Dalton gave the atomic theory. According to this theory, all substances are composed of indivisible atoms. Atoms of the same element have the same properties. In contrast, atoms of different elements have different properties. Atoms of other elements combine to form compounds.
At the end of the eighteen century, many scientists suggested that gases’ behavior could be explained better by considering them as the collection of particles. Except for Dalton’s atomic theory, the kinetic theory of gases explained how gases behave physically.
In 1897, Joseph John Thomson found that cathode rays are not electromagnetic rays. He studied the properties of cathode rays. He discovered that these rays are made up of particles. These particles are 1800 times lighter than hydrogen. These rays were deflected toward the positive plate in a cathode ray tube. This showed that cathode rays are negatively charged. He concluded that these particles came from atoms. He called these particles corpuscles.
In 1904, J.J. Thomson proposed the plum pudding theory. According to this theory, many negatively charged electrons are suspended throughou it in a sea of a positive charges. This will give an atom an overall neutral charge. Thomson resembled his model with plum pudding. Therefore, this theory is called plum pudding theory.
In 1911, Rutherford and his colleagues Hans Geiger and Ernest Marden performed alpha particles scattering experiment. In this experiment, they bombarded thin foil of metal (gold) with alpha particles. A large number of alpha particles passed through the foil undeflected. Some particles deflected at a larger angle. A few of them were bounced back. This showed that the positive charge is concentrated at the center. This positive charge center is called the nucleus. Rutherford measured the size of the nucleus of the gold, which is almost 10,00 times smaller than the size of the entire atom. Thus the entire atom is almost empty. Its entire mass is concentrated at its center.
In 1913, Neils Bohr discovered its model. According to this model, electrons revolve around the nucleus in orbit with a specific energy. Electrons can jump between these orbits by the absorption or emotion of a photon. This model was the first model describing its overall structure.
In 1926, Erwin Schrodinger discovered its powerful model. He gave a mathematical model for the distribution of electrons in an it. This model consists of mathematical equations called wave equations that satisfy the behavior of electrons. Bohr’s model was 1-dimensional. It used one quantum number to describe the behavior of an electron in it. Schrodinger’s model is 3-dimensional. It used three quantum numbers to explain the behavior of electrons in it.
In 1913, Fredrick Soddy found that more than one type of it appeared at each position in the periodic table. Margaret Todd used the term isotope for different of them that belong to the same element. J.J Thomson discovered a technique for the separation of isotopes.
In 1938, Otto Hahn bombarded neutron on uranium to get transuranium elements. Instead, he hot barium as a product. In 1939, Lise Meitner and Otto Frisch verified that Hahn’s result was the first nuclear fission reaction. In 1950, particle accelerators and particle detectors were developed. These instruments helped scientists to study them moving at high energies.