By; Paige Davis
From ancient philosophy to modern quantum mechanics: the atom’s evolution
Everything that has ever existed is made up of atoms. Atoms are known as the building blocks of the universe. From the smallest grain of sand to the largest planet, every object is made up of countless atoms interacting. They are tiny and unseen, yet endlessly powerful. Understanding them helps us learn the story of everything: how materials form, how energy moves, and how living organisms function.
From early philosophical ideas about indivisible particles to modern quantum theory, the story of the atom demonstrates our curiosity about the existence of everything. By exploring the history of the atom, we can better appreciate not only how the universe is built, but also how deeply everything is connected at the smallest level.
Dating back to 400 B.C, Democritus, a Greek philosopher, created the word “atomos,” which means indivisible or uncuttable. He also proposed the atomic theory which states: “all matter is composed of indivisible particles”. His theory laid the groundwork for modern atomic theory.
Over time the model of the atom has evolved from a simple philosophical idea to a complex and scientifically supported theory
Fast forwarding over 2000 years later, a man by the name John Dalton formulated with the first scientifically based model. In 1803 Dalton proposed that atoms were tiny spheres. He stated that atoms in the same element were identical to each other in terms of mass and chemical properties.
94 years later, J.J. Thomson introduced his Plum Pudding Model of the Atom.
Thomson discovered electrons while using cathode ray tubes. Thomson defined electrons as subatomic particles with a negative charge. In this model, the atom consists of a positive mass that electrons attach themselves to, like plums in a cake.
A few years after this in 1911, chemist Ernest Rutherford had an experiment
where he fired alpha particles (helium nuclei) at a thin sheet of gold. The results were that several alpha particles were significantly deflected and even bounced back. Rutherford concluded that the atoms contained a small, dense, positively charged nucleus at their center, which concentrated most of the atom’s mass.Rutherford proposed a model whereelectrons are orbiting around a larger dense nucleus, like a miniature solar system.
Two years later, in 1913 Niels Bohr took Rutherford’s model one step further andrealized that the electrons move in discrete quantized orbitals around the nucleus. Each orbit corresponded to a specific energy level for the electrons. He discovered that when an electron absorbed energy, it jumped to a higher energy level and when it emitted energy, it returned to a lower energy level. He also discovered protons, which are a positive subatomic particle located in the nucleus.
In 1926, Erwin Schrödinger posed the model of the atom that we use today. Schrödinger discovered that electrons do not have defined trajectories or obits but are instead described by wave functions that represent the probability of finding them in different positions. He called these wave functions “orbitals”. There are several types of orbitals that have different characteristic shapes and probability distributions. In these orbitals there are nodes where the probability of finding an electron is zero. This model is known as the Quantum Mechanical model of an atom.
The last addition to the model came in 1932 when James Chadwick discovered that in the nucleus of an atom there weren’t just protons but also neutrons, a neutral subatomic particle.
Over time the model of the atom has evolved from a simple philosophical idea to a complex and scientifically supported theory. Each discovery about atoms has helped deepen our understanding of the world around us. The history of the atom has demonstrated humanity’s drive to understand and discover all there is to know about everything and anything around us, even the things unseen to our eyes.