Story of the atom

The Greek philosopher and physicist Democritus proposed the idea of an atom at around 440 B.C. The atom is first explained by him using a stone. When a stone is split in half, it becomes two separate stones. There would eventually come to be a portion of the stone that would be too small to be cut if it were to be cut continuously i.e., indivisible. Since then, many scientists have adopted, discarded, or published their own theories about the nature, structure, and size of atoms.

However, the most widely accepted, and still the basic model used to study atoms is Rutherford’s model. Rutherford published his theory of the atom suggesting that it had an electron orbiting a positively charged nucleus. This model was created after a series of experiments which included shooting alpha particles at thin gold sheets. Most of the alpha particles flowed through with little disturbance, but a tiny fraction was scattered at extreme angles to their initial direction of motion. Rutherford calculated the estimated size of the gold atom's nucleus and discovered that it was at least 10,000 times smaller than the atom's total size, with a large portion of the atom made up of empty space.

This theory paved the way to further the atomic models by various other scientists. (Figure 1)

Researchers have discovered unidentified molecules in space which are believed to be the precursor of all chemistry in the universe. The earliest "atoms" in the cosmos were actually nuclei without any electrons. The universe was incredibly hot and dense in the earliest seconds following the Big Bang. The quarks and electrons that make up matter first appeared when the cosmos cooled, and the ideal conditions were met for them to do so. Protons and neutrons were created by quarks aggregating a few millionths of a second later. These protons and neutrons joined to form nuclei in a matter of minutes. (Figure 2)

Things started to happen more slowly as the cosmos cooled and expanded. The first atoms were formed 380,000 years ago when electrons were locked into orbits around nuclei. These were mostly hydrogen and helium, which are still the elements that are found in the universe in the greatest quantities. Even now, the most basic nucleus, found in ordinary hydrogen, is only a single, unadorned proton.

There were other configurations of protons and neutrons that also developed, but since the number of protons in an atom determines its identity, all these other conglomerations were essentially just variations of hydrogen, helium, and lithium traces.

To say that this is an exciting time for astrochemistry is an understatement. Furthermore, the formation mechanism of amino acids and nucleobases is being demonstrated by laboratory simulations of interstellar environments. Now that we are finding answers to these known

problems, even more are arising.

Hopefully, a more thorough understanding of these chemical processes will enable us to make more precise deductions about the general history of the universe and astrophysics.

Written by Navnidhi Sharma

REFERENCES

CERN (n.d.). The early universe. [online] CERN. Available at:

https://home.cern/science/physics/earlyuniverse#:~:text=As%20the%20universe%20continued%20to.

Compound Interest (2016). The History of the Atom – Theories and Models | Compound Interest. [online] Compound Interest. Available at: https://www.compoundchem.com/2016/10/13/atomicmodels/.

Fortenberry, R.C. (2020). The First Molecule in the Universe. Scientific American. [online] doi:

https://doi.org/10.1038/scientificamerican0220-58.

Sharp, T. (2017). What is an Atom? [online] Live Science. Available at:

https://www.livescience.com/37206-atom-definition.html.