Why are there electrons in the atom

Atoms, electrons and ions

Around 500 BC (BC) the Greek natural philosopher Leukippus introduced the term atom. The atom is derived from the Greek atomos, which means "indivisible". Today we know that atoms are divisible and are made up of an arrangement of neutrons, protons and electrons.

Atomic models

Back then, at the time of Leukippus, as well as today, almost all definitions and explanations about atoms and atomic models are of a more theoretical nature. It is not uncommon for atomic models to be used to make inexplicable effects or mechanisms of an atom plausible.
In 1911 Rutherford developed the atomic model with a core and a shell. According to his assumption, the atomic nucleus consisted of the entire positive charge and the negatively charged electrons orbit the nucleus in a shell. The centrifugal force of the circling electrons should dissolve the force of attraction through the nucleus and thus keep the electrons in their path.
In 1913 the Danish physicist Niels Bohr calculated the different energy levels in an atom. He developed the Bohr model of the atom. He agreed with Rutherford that atoms consist of a core and a shell. The only difference is that the electrons circle on several orbits, also called shells.
The Bohr model of the atom is described in the following text.

Atom / atoms

An atom is the smallest building block of the chemical elements. There are well over 100 different atoms that have a similar structure.
Atoms are made up of an atomic nucleus and an atomic shell. The structure is comparable to a planetary system: A sun, that should be the atomic nucleus around which the planets rotate (atomic shell).
The atomic nucleus is in the center of the atom. It is positively charged and contains almost the entire mass of the atom. It is made up of protons and neutrons.
The atomic model shown here is the Bohr atomic model. It is a view of how electrons, protons and neutrons relate to each other. It is assumed that electrons rotate on a fixed path around the atomic nucleus.
Neutrons are electrically neutral particles. They only occur in the atomic nucleus because they are not stable in the free state. The number of protons in the atomic nucleus is always the same number of electrons in the atomic shell. Protons also exist in the free state.


The atomic shell is made up of electrons. The electrons are electrically negatively charged particles. The electrons on the outermost ring (shell) of the atom are called valence electrons. The flow of electrical current in conductive material corresponds to the movement of the valence electrons.
An atom is electrically neutral to the outside world. The atomic nucleus and the atomic shell have the same number of electrical charges (protons and electrons).


Atoms with more electrons than protons or more protons than electrons are called ions. The word ion comes from the Greek and means the wanderer.
Atoms that are positively or negatively charged, i.e. not electrically neutral, can attract or repel each other. That means they can be moved. At atoms with a negative charge one speaks of an excess of electrons. In the case of atoms with a positive charge, one speaks of an electron deficiency.

If electrons are removed from a neutral atom, the atom has more positive than negative charges. The atom attracts negative charges and repels positive charges.

If electrons are supplied to a neutral atom, the atom has more negative than positive charges. The atom attracts positive charges and repels negative charges.

The following joke: Two atoms are walking down the street. One says, "Uh oh, I've lost an electron." The other says, "Are you sure?" "Yes, I'm positive."

charge carrier

Charge carriers are very important for electrical current. An electric current can only flow if there are enough free charge carriers. Charge carriers can be electrons (metallic charge carriers) and ions (liquid charge carriers).

Which atomic model is correct?

Most atomic models are outdated and can still be valid. Bohr's atomic model is such a case. But it is still sufficient to understand many explanations in physics and electrical engineering.

Every model always has a range of validity within which its accuracy is sufficient. At the same time, a model defines the basic understanding for the next higher model.
The "disc" model for the earth is still justified today. Anyone who wants to drive across the country is not interested in the curvature of the earth, which is why a map is much more practical than a globe.
It is different with seafaring. Navigation must at least take into account the spherical shape of the earth. Only in satellite technology does it actually play a role that the earth is actually rather egg-shaped.

In principle, one chooses the model that describes the existing problem sufficiently precisely or to represent a property in an understandable manner. If necessary, you have to choose another model that is more suitable or more precise.

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