Atomic Physics 101: Puddings, atomic models, structures, and their histories!
We will learn about the 6 evolutions of the Atomic Model, and about the structure of an atom!
Introduction
After the Renaissance, the interest in modern science increased. Every scientist was trying to answer the one simple thing. What is the last particle that we get if we take a piece of paper and keep cutting it, or what is the fundamental particle that makes up everything.
It was discovered that atoms are the particles they were looking for and they have certain properties that cause the intramolecular (in a molecule) and intermolecular (between molecules) forces.
The History of Evolution of The Atomic Model
In this section, we will learn about the history of the evolution of the atomic model.
1. 400 BC: Democritus — Atomos
Around 400 BC, Democritus, an ancient Greek philosopher, proposed the concept of Atomos (which means “uncuttable”), very small invisible particles that made matter. He believed them to be of varying sizes, but solid spheres.
2. Early 1800s: John Dalton — Atoms
John Dalton, the father of Atomic Theory, revived the idea of atoms and proposed that each element consists of identical atoms that combine in fixed ratios to form compounds.
For example, in H2O (water), the ratio of Hydrogen atoms to Oxygen atoms is 2:1.
3. 1897: J.J. Thomson — Plum Pudding Model
J.J. Thomson discovered the electron, suggesting that atoms have smaller particles within them. He suggested that the body of the atom is round and has a positive charge, and that electrons, containing negative charges, are scattered evenly throughout the atom like raisins in a plum pudding.
He said that the positive charge of the body and the negative charge of the electrons cancels out, making atoms neutral.
4. 1911: Ernest Rutherford — Nuclear Model
The Rutherford model of the atom was established after the Gold Foil experiment, which was performed to discover the nucleus. After the gold foil experiment, it was concluded that there is a nucleus in the atom, and that the positive charges are in the nucleus. They concluded that the electrons are in a cluster surrounding the nucleus.
This was possible by shooting alpha particles (helium nucleus) at a gold foil and see if they would go through. If they went through, then there were just electrons and the body is positive. If they were reflected, then it means there is a nucleus in the center. They used a detecting screen to detect bounced particles.
The results showed that the particles were being bounced, so they concluded that there is a nucleus in the atom. So, protons (positively charged particles) were discovered!
5. 1913: Niels Bohr — Bohr’s Model
Niels Bohr discovered the atomic model that is thought in most schools. The model has energy levels / shells, in which electrons are in pairs. We will learn more about this model in section 2. This is the model used for simpler purposes and the general idea of atoms.
6. 1920s: Erwin Schrödinger — Quantum Model
This model changes everything. Until now, this was just atomic physics, but now Quantum Mechanics comes in.
You can read my article on quantum mechanics to learn more about it.
Quantum Mechanics 101: Uncertainty, Waves, and Lots of Cats!
In this model, the electrons are not just particles, they exist as a cloud of probabilities. Read the article about quantum mechanics to learn more about it.
The Structure of an Atom
In this section, we will understand the widely known Bohr’s Model, which is the latest model if we don’t count quantum mechanics, and which is taught in school.
Nucleus
In the atom, there is a nucleus, consisting of protons and neutrons. There are equal number of protons and neutrons in the nucleus, unless it’s an isotope. The protons have a positive charge, and the neutrons have neutral charges.
Protons and Electrons
There are equal number of protons and electrons in an atom, and electrons have a negative charge. Thus, the charges cancel out, and overall, the atom is neutral.
Electrons
In Bohr’s Model, the electrons are in energy levels or energy shells. These are different orbits of electrons that have different number of electrons.
The maximum number of electrons a level can hold is given by the formula:
where n is the number of the level.
But because of the Octet rule, in a stable atom, there are only eight in each level, except for the first level, where 2n² is 2.
Isotopes
Isotopes are like different species of atoms belonging to the same element. In them, the atomic number (number of protons) is the same, but the atomic mass (sum of protons and neutrons) changes. This is because the number of neutrons changes.
Ions
Ions are formed when an atom gains or loses an electron to another one. This happens by chemical reactions. Previously, the number of protons and electrons was the same. But if an electron gets added or reduced, then the balance will be lost, causing the atom to have a charge, and making it an ion.
If an electron is gained, then the number of electrons is greater than the number of protons, and this makes the charge of that ion negative. If an electron is lost, then the number of protons is greater than the number of electrons, and this makes the charge of that ion positive.
Negative ions are known as anions, and positive ions are known as cations.
Conclusion
So, there you go! Now you know atomic physics, or the basics. Read my article about quantum mechanics to understand about Schrödinger’s quantum model.
If you want more content like this, comment and ask for the topics!
Read next: