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Even if we were to use the most capable and powerful microscopes to see tiny particles, atoms are so small that using these microscopes would be insufficient to see them. Scanning electron microscopes have been able to capture images of moving atoms, for example two rhenium atoms joining to form a molecule. In any case, what was captured is practically “unrecognizable”, as can be seen in the last three references of the article.
Therefore, experiments to discover the structure and behavior of atoms must be carried out with large numbers of them. From the results of these experiments, we can try to build a hypothetical model of an atom that behaves like the real atom.
Molecules are made up of one or more atoms, joined by covalent or other bonds. Thus, atoms can be represented by circles with a nucleus in the center. This nucleus contains protons and neutrons. In addition, it is surrounded by one or several external zones that represent the “envelopes” or “levels”, which are technically called atomic orbitals, in which the electrons that surround the nucleus of the atom are found.
Chemical Definition of Atom
The atom is the smallest particle of an element, which may or may not have an independent existence but which always participates in a chemical reaction . An atom is also defined as the smallest unit that retains the properties of an element.
On the other hand, all the atoms of the same element are identical, and different elements have different types of atoms . The atoms, when ionteracting, produce chemical reactions.
How is an atom formed?
Protons, neutrons, and electrons are known as subatomic particles. These particles are responsible for the formation of atoms. From a quantum point of view, the enumerated subatomic particles are constituted in turn by other even more elementary ones, whose study corresponds to fundamental Physics. Neutrons and protons have roughly the same mass, while the mass of an electron is negligible in comparison. On the other hand, while an electron has a negative charge and a proton has a positive charge, a neutron has no charge. Now, an atom contains the same number of protons and electrons, and therefore, as a whole, an atom has no charge.
On the other hand, the nucleus of an atom only contains protons and neutrons, so it is positively charged. Electrons, for their part, occupy the region of space surrounding the nucleus. Therefore, most of the mass is concentrated in the nucleus, which is the center of the atom. The nucleus contains neutrons and protons, which give the atom its mass and its positive charges. A neutron has no charge and has a mass that is considered unity.
The proton carries a single positive charge and also has a mass of one. Thus, the atomic number of an element is equal to the number of protons or positive charges in the nucleus. On the other hand, there is the atomic weight of an element. This is determined by adding the total number of protons and neutrons in the nucleus (remember that the mass of electrons is negligible in comparison).
By contrast, an electron has a single negative charge. For the atom of an element to have zero charge, it must have the same number of electrons as protons. These electrons are arranged in zones (orbitals) around the nucleus of the atom.
How big is an atom?
The size of an atom is extremely small. A layer of atoms as thick as a thin sheet of paper is made up of billions of atoms. It is impossible to measure the size of an isolated atom because, as quantum physics demonstrates, it is impossible to precisely locate the positions of the electrons surrounding the nucleus.
However, it is possible to calculate the size of an atom by assuming that the distance between neighboring atoms is half the radius of that atom. Atomic radius is usually measured in nanometers (nm):
1m = 10 9nm
Dalton’s atomic theory
Dalton’s atomic theory is a scientific theory of the nature of matter proposed by the English scientist John Dalton in 1808. With this theory, Dalton established that all matter was made up of small, indivisible particles called “atoms.”
In the theory proposed by Dalton, the scientist suggests that all substances are made up of atoms and that atoms are units that cannot be divided or destroyed. This theory also proposes that, although all elements are made up of atoms of different sizes and masses, all atoms of the same element have the same size and mass.
Dalton’s atomic theory has other postulates, these are indicated below.
- Matter is made up of tiny particles called atoms.
- Atoms are indivisible particles that cannot be destroyed or created by chemical reactions.
- All atoms of an element have identical chemical properties and masses, while atoms of different elements have different chemical properties and masses.
- Atoms combine in small whole ratios to form compounds.
- Matter is everything in our environment. It has basic structural and fundamental units, precisely atoms.
This theory, key to understanding the nature of matter, has been widely superseded by, among others, quantum mechanics. However, it continues to be a useful tool to understand the macroscopic properties of matter and most of the phenomena that Chemistry studies.
Conclusion
To finish understanding what an atom is, let’s examine the concept of matter with an example.
Let’s take a storybook and break down its structure. The book contains many pages, each page is made up of paragraphs, and each paragraph contains many sentences. Each sentence will then have many words and each word will have characters, that is, letters.
It is exactly the same case when we consider matter from the point of view of Dalton’s theory, that it can be divided into molecules, which is the smallest thing a substance can be divided into without losing its essence. Molecules, in turn, are made up of one or more types of atoms. Atoms, which are the smallest particle of an element, are made up of subatomic particles: protons, electrons, and neutrons.
Sources
- Leal, S. (2010). Constitution of matter .
- Molina, R. (sf). the atom . Institute for the Structure of Matter.
- Planas, O. (2013). What is a molecule ?
- https://www.larazon.es/ciencia/20200131/fie2hkdhebefrgg67mcaht7fvy.html
- https://wp.icmm.csic.es › 2009/02 › seeing_atoms (pdf)
- https://www.europapress.es/ciencia/laboratorio/noticia-nitidez-imagen-atomos-alcanza-niveles-limite-20210521164505.html
