What do we know about the atom? Structure, atomic models, and more
Atoms are a clear example of how something so small can determine who you are. To understand their structure and behavior, many scientists throughout history have developed different atomic models, each one more accurate than the last.
In this article, we will explore the discovery of the atom and how our understanding of it has evolved through the different atomic theories.
What is an atom?
Simply put, an atom is the smallest unit into which an element can be divided without losing its properties. Atoms are made up of three particles: electrons, protons, and neutrons. In turn, protons and neutrons are made up of even smaller particles called quarks.
Atomic structure
Let’s look at the two main parts of the atom:
Nucleus: At the center of the atom is the nucleus, which contains positively charged protons and neutrons, which have no charge. Even though the nucleus accounts for 99.9% of the atom’s mass, it occupies only a small portion of its total volume.
Electron cloud: Surrounding the nucleus is the electron cloud, negatively charged particles. Even though electrons have a much lower mass than protons and neutrons, they occupy most of the space in the atom.
What is a molecule?
When atoms join together, they form molecules. The combination of atoms can give rise to different substances. For example, a hydrogen peroxide molecule (H₂O₂) is composed of two hydrogen atoms and two oxygen atoms. If one of the oxygen atoms is removed, we obtain a water molecule (H₂O). This demonstrates how a small change in atomic composition can generate a completely different substance.
History of atomic models
The concept of the atom has changed significantly throughout history. Below, we will explore some of the most important atomic models.
Atomic Model of Democritus
The first time that the atom was mentioned was in ancient Greece, thanks to the philosophers Democritus and Leucippus. They proposed that matter could be divided into increasingly smaller portions until reaching a particle that would be indivisible. They called this particle “atom”, a word that comes from the Greek atomos, which means “indivisible”.
Dalton’s Atomic Model
However, the first atomic model was proposed by the British chemist John Dalton in the 19th century. According to Dalton, atoms were solid spheres that, when joined together, formed chemical compounds.
In addition, he established that there are different types of atoms and that all atoms of the same element are identical to each other.
Thomson’s Atomic Model
The discovery of the electron in 1897 by the British physicist Joseph John Thomson changed the panorama of the atomic model. Through experiments with cathode rays, Thomson discovered the electron, a negatively charged particle that has a mass much smaller than that of the atom.
He proposed that the atom was made up of a positively charged mass within which electrons were embedded. Although we now know that this is not exactly the case, this model helped explain phenomena such as light emission and electrical conduction.
Rutherford’s atomic model
In 1911, Ernest Rutherford proposed a new atomic model. His theory described the structure of the atom as a system similar to the solar system, with a central nucleus in which electrons orbit around it.
He was also the first to identify the proton, which determines the atomic number (Z) of an element. For example, oxygen has 8 protons, so its atomic number is 8.
Bohr’s Atomic Model
In 1913, Danish physicist Niels Bohr proposed a model that refined Rutherford’s. According to Bohr, electrons orbit the nucleus in specific energy levels or shells.
Unlike earlier models, Bohr explained that electrons could move between these levels by absorbing or emitting energy in the form of electromagnetic radiation.
Schrödinger’s Atomic Model
In 1926, Erwin Schrödinger developed an atomic theory based on quantum mechanics. This model replaced Bohr’s defined orbits with a “probability cloud,” where the exact position of an electron cannot be determined. Only the probability of finding it in a region around the nucleus can be known.
Other Atomic Models
Four years later, in 1930, Paul Dirac developed a relativistic atomic model that incorporated the effects of relativity into quantum mechanics. Later, in the 1960s, the molecular orbital theory emerged, and in the years since, models such as the theory of general relativity applied to the atom have been proposed.
The future of atomic models
The concept of “atom” began with the idea of an indivisible particle, but atomic theories developed over the centuries have shown that atoms are composed of even smaller particles: subatomic particles.
Although Democritus’ original idea has changed, his ideas were essential to the development of chemistry. As our scientific understanding increases, new atomic models are likely to emerge that delve even deeper into the structure of the atom and its behavior.
