How did Rutherford discover the proton

Ernest Rutherford atomic model

This article deals with the Rutherford atomic model. It is a model by the scientist Ernest Rutherford of the structure of an atom. Before that, however, we will explain some of the basics on this topic to you in order to understand this atomic model well. This is an article on the basics of chemistry.


First a small note: This article is part of our series Atomic Models of Chemistry and describes the Rutherford atomic model. The link just mentioned is available for everyone who is also interested in other atomic models. Back to Rutherford model: This was set up in 1911 on the basis of the knowledge acquired by natural scientists up to that point. For a better understanding of the model, we will first explain some important terms to you.

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Positive and negative charge

Many people know it: When you style your hair, the comb and hair are oppositely charged and therefore attract each other. So you can lift the comb up and some hair will "stick" to it. The word "opposite" has already expressed that there are two different types of charge gives. The positive charge is marked with a plus (+), the negative with a minus (-). The same charges repel each other, dissimilar charges attract each other.
Up until the end of the 19th century, positive and negative charges were known, but their causes were not known. It was not until the Englishman Thomson found out that the negatively (-) charged electrons are part of matter. It was also known that electrons can "pass" from one substance to another. If a substance now has an excess of electrons, it has a negative effect on the outside. The other substance, however, then has a positive effect.
By nature, substances are not charged to the outside, one then speaks of electrically neutral. However, since it was found out that atoms contain negatively charged electrons, the question now arises: How can the atom with a negative part of the charge be neutral overall. The answer is very simple: there must also be a positive part in an atom.
The FrenchBecquerel also succeeded in determining three different types of particles in 1896. He was a co-discoverer of the natural radioactivity and found that these consist of three different types of particles. The first part was attracted by a negative electrode, so it had to be electrical positive be charged. The second part was attracted to the positive electrode, so it had to negative be. That leaves the part that was not even attracted and therefore electrical neutral was. The three types of particles were then referred to as α-particles (pronounced: alpha-particles), β-particles (pronounced: beta-particles) and γ-particles (pronounced: gamma-particles).

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Atomic model according to Rutherford

Knowing this led now Ernest Rutherford carried out one of the most famous experiments in physics and chemistry. He had an extremely thin sheet of gold on hand, about 1,000 atomic layers thick. He shot alpha particles at them and watched them spread on a film strip behind the gold foil. He had a big surprise for him: Most of the alpha particles flew straight through the foil. However, some were "distracted" and ended up in a completely different place on the filmstrip. The explanation: The alpha particles are deflected when they fly close by and land at other points on the strip. In the case of a "direct hit", the alpha particles are even reflected and continue to fly in completely different directions.

These findings from Rutherford led to his Core-shell modelwhich explains the basic structure of an atom. An atom has a positively charged nucleus. These positive parts got the name Protons. Circle around the core Electrons on circular paths and represent the negatively charged part of the atom. If an atom appears electrically neutral to the outside, the proportion of positive and negative charges must be the same!
It was also found that elements have different numbers of protons. The different Proton number is also known as Atomic number designated. It was also found that the alpha particles used for the experiment were two atomic nuclei of helium. Due to the double charge, it was possible to infer two protons. Their experimentally determined four-fold mass (compared to a proton) indicated that the nuclei - there is one exception - contain so-called neutrons in addition to the protons. Protons and neutrons are summarized Nucleons (from Latin nucleus - nucleus).

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