Atoms are the components of everything in the Universe: the galaxies, the nebulae, the stars, the Sun, the planets, the Earth and the human.

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All matter is made up of atoms

Since the beginning of the 20th century it has been known that all matter is made up of atoms. Everything in the Universe: the galaxies, the nebulae, the stars, the Sun, the planets, the Earth, the mountains, the trees, the sea, the clouds, the atmosphere and ourselves, everything is made up of atoms.

Nebula M78
Nebula M78 in the constellation Orion. Image obtained by Ignacio de la Cueva Torregrosa, amateur astrophotographer from Ibiza.

In those years it was discovered that atoms are made up of a very small nucleus with a positive electric charge, where almost all the mass is concentrated, and a cloud of electrons with a negative electric charge.

Atoms are the constituents of matter

Since the time of the first known Greek sages, matter was thought to be made of tiny particles, which were called atoms.

At the beginning of the 20th century, the most popular image spread that atoms are divisible and that they are composed of a nucleus (made up of protons and neutrons), and electrons that revolve around the nucleus.

Atomic models have been refined since Ernest Rutherford proposed this model, which was accepted by the scientific community.

Nucleus ofHelium atom, with two protons and two neutrons. Credit: Wikipedia

Model of the atom according to Ernest Rutherford

In 1911, Ernest Rutherford made his greatest contribution to science, publishing the hypothesis that in the center of the atom there must be a “nucleus” that contains the positive charge of the atom, and that there is also a negative charge based on electrons orbiting around the core.

atoms litium
Lithium atom with 3 protons and 3 electrons. Credit: web

Protons are in the nucleus of an atom

Protons and neutrons together are known as nucleons, since they make up the nucleus of atoms.

The number of protons in the nucleus of an atom determines what chemical element it is and its chemical properties.

  • The hydrogen nucleus has 1 proton.
  • The nucleus of helium has 2 protons.
  • The nucleus of lithium has 3 protons.
  • The nucleus of carbon has 6 protons.
  • The nucleus of oxygen has 8 protons.
  • The nucleus of iron has 26 protons.
  • The nucleus of gold has 79 protons.
The nucleus of an atom with many protons. Credit: web

The protons in a nucleus should repel each other, since they have an electric charge of the same sign (+1).

However, they remain tightly bound together, due to the fact that they undergo the action of a force called a strong nuclear interaction.

Atomic theory states that 118 is the maximum number of protons that can be in the nucleus of an atom.

On December 30, 2015, the discovery of the heaviest possible synthetic element obtained in a laboratory was announced. It was given the name Oganesón, in honor of the Russian physicist, Yuri Oganesián.

atoms 118
The nucleus of oganeson (Uuo) surrounded by a cloud of 118 electrons. Credit:

Electrons orbit the nucleus of an atom

In stable atoms, for every proton in the nucleus, there is one electron orbiting it. In the nucleus of the carbon atom there are 6 protons. Around it, 6 electrons orbit.

atoms electrons
Carbon atom with 6 protons and 6 electrons. Credit: web

As the electric charge of the proton is opposite and equal in absolute value to the charge of the electron, the electromagnetic force causes the electrons to remain united around the nucleus of the atom.

Model of the atom according to Niels Bohr

Taking Rutherford’s model as a starting point, Niels Bohr tried to incorporate into it the theory of “quanta of energy” (developed by Max Planck) and the photoelectric effect (observed by Albert Einstein).

atoms bohr
Diagram of the atom according to the Bohr model. Credit: Wikipedia

Standard model of the atoms in the 21st century

Well into the 20th century, scientists continued to explore the properties of the atomic nucleus and discovered that it was made up of tiny quarks.

For that, they needed microscopes that allowed them to see with a precision of 10 -17 cm. This is the scale of precision that has been reached by now.

Standard model of matter and atoms

The so-called “standard model” of particle physics is a theory in the making, which can explain a lot about how the known world is made and how it works.

In the 1960s, researchers made a series of observations that led them to outline theories about the existence of elementary particles. They developed a standard model of the matter.

The most important elements of the standard model fell into place over some twenty years, beginning in the early 1970’s, when the experimental results were fitting with the theoretical ideas that had been raised since the previous decade.

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