1 - Energy States of Atoms
Abstract (TL;DR):
We all know about the atom and some of us even know the three subatomic particles — protons, neutrons, and electrons — that make up atoms. This article talks about the atom from the standpoint of explaining why the atom behaves how it does.
Atoms communicate through the use of its electrons, which are oriented in specific ways according to their energy state. Since atoms and their electrons naturally want to be at their lowest energy states, electrons behave in ways that get them there, creating beautiful shapes called “orbitals”.
Image via nickvdg
Updated (3/2025)
How does one explain the relationship between one element and another? Sure, you could use the word “electrostatic” or explain it by going into depth about “electronegativity”, but those aren’t immediately relatable. If I were to put an explanation into more understandable words, I would say that it’s a game of sharing - sharing that happens the same way almost every single time according to both size and state of matter. Some reactions occur naturally just by distance. Some may only occur in the present of some outside energy source like heat. Reactions between the elements, thus, play a game of give and take.
But give and take what? And why? These questions define atomic relationships and, by extension, the way our world and our universe has formed and will continue. So, for the “beginning” of our journey, let’s try to answer those questions.
Negative Electron Affinity
There’s a currency that atoms utilize to communicate with each other - the electron. The electron is a mass that has a negative charge, which, like the two ends of a magnet, means that it is attracted to masses with positive charges and can’t stand other negatively-charged masses.
Image via ChemistryJokes
In fact, it’s a positive charge that keeps the electrons from flying away. The core of any atom - the nucleus around which electrons move - is normally composed of protons and neutrons (excluding hydrogen, which has a nucleus only composed of a proton), the former being positively charged and the latter having no charge. The dance that these particles undergo will be the subject of our attention in a future arc, but, for now, let’s focus on the electron - the atom’s currency, as I’ve called it. You can think of these electrons as a mode of “communication” between atoms. Sometimes that communication can be a bit rocky - electrons are very finicky when it comes down to it. Your professors and teachers may have used words like “valence shell” and “orbital”, which sound downright scary if you’re uninitiated, but we'll take it from the top (and I promise to make this more painless than your instructors tried to).
Explosions occur as built-up energy is suddenly released.
In order to properly understand the atom, we have to start with an observation that holds true for every system in the universe - lower energy is the ultimate goal. Everything you see in the world follows this principle. It is why when a fast-moving car (the energy of motion) crashes, you hear sound (a type of energy) corresponding to the speed it was moving. Energy represents the stability of a system and the less of it you have, the more stable you are. Said another way, if a system built up energy and could not release it, for whatever reason, it would be considered unstable. That’s when you get explosions.
However, there is a problem. Since electrons are negatively charged and protons are positively charged, you would reasonably think that, if you’re an electron, the best place to be is right up against the proton. In fact, in a classical understanding of physics, if electrons simply orbited the nucleus, much like planets orbiting stars, it would make sense that they would just, eventually, fall in. However, experiments have shown that electrons don’t actually behave like planets around stars (and we will get into their behavior in a future section). Instead, their different energy states are found in particular spaces around a nucleus. Those states are called orbitals, which are the paths that an electron takes according to the number of surrounding electrons and protons within the nucleus.
There are even more reasons, particularly in the realm of quantum mechanics, that explain the presence of orbitals, but we’ll go over two of the most important.
The Game of Energy
The Electric Force - The Force of Attraction or Repulsion
There is a formula out there that explains the electric force that keeps electrons apart and attract electrons to the nucleus.
Coulomb’s Law. The force, F, has the unit of newtons, named after Sir Isaac Newton, who created the foundational equation for force.
This is Coulomb’s Law. We will go through the terms of this equation in full.
First, most notably is k, the Coulomb Constant. A constant, if you are unaware, is a fixed value, usually represented by a letter or sign. The constant in this equation, k, will always represent a value of 9 x 109 N*m2/C2. (N is newton, a unit of force, m is meter, a unit for distance and C is coulomb, a unit for charge).
Next, we have both q values. These represent the quantity of the charges between the two particles being compared. These charges have the same value, but opposite signs, according to if the charge is a proton or electron. There can be more than the two q values shown in the equation above.
Last is r, or the distance between the particles.
Now, these values, after being determined experimentally, can be put into the above equation and an electric force, F, can be quantified, but the important part here is the sign of the force, or whether it is positive or negative. If the force is positive, the two particles repel each other, and if it is negative, the two attract each other. Electrons that are near each create a positive electric force, meaning they repel, and their energies rise when near each other. That, as we know, is no good.
The higher the repulsive force, the more likely they are to distance themselves in order to lower that total energy. The distances between these electrons form the energy levels that we talked about before - orbitals explained with math!
Potential and Kinetic Energies
To further explain why an electron occupies a space rather than orbiting in a conventional sense, we need to return to our old friend “energy”. When an electron is farther away from the nucleus, it has a large amount of “stored energy”, or potential energy. This potential energy is the energy that propels the electron towards the nucleus. As it moves, the potential energy converts to the energy of motion, or kinetic energy.
Austrian skydiver Felix Baumgartner
Image by Ms. Lintan via Tumblr
High potential energy up there, high kinetic energy on his way down…
Imagine an electron very close to its nucleus. Our newly-acquired Coulomb’s Law would tell us that the amount of force on that attractive force electron would be nearly infinite (after all, “r”, the distance between our electron and protons in the nucleus, would be very low). This force is proportional to the amount of kinetic energy that electron contains — that is, it moves infinitely fast the closer it is to the nucleus. In this state, it’s impossible for the electron to exist in a stable low energy state. In reality, we need some kind of balance between potential and kinetic energies to minimize the total energy, and keep the energy state of any given electron low. That is what we define as an orbital, a position for an electron where it’s kinetic energy and potential energy are as low as they reasonably can be.
The Electron Cloud
Image via Byju’s
I hate to burst bubbles (except in cases like this), but this classic image above is actually an inaccurate representation of the atom. Electrons have properties that make their exact positions impossible to identify. In fact, these jewels of the quantum world could be in one place, a second, or a third, or all three places at the same time! In actuality, we can only tell where an electron probably will be. So, a more accurate representation looks like this:
Image via Couts G8 Class
This model, the Electron Cloud model, is brought to you by Erwin Schrödinger. Yes, the same one with the cat and the box. Or was there a cat in that box…?
Orbital Chemistry
Now that we understand why they form, we can delve into them more closely in future articles. In this article, we’ve treated the electron as a particle; however, that doesn’t fully describe it. We’ll also see that, according to the positions that the electrons occupy in an atom, the electron’s “clouds” can look different. The cloud above, for example, represents the orbital configuration that one would see in a lithium atom, but we there are tons more. For now, enjoy this sneak peek at what is coming next.
Image by Donald A. McQuarrie via “Quantum Chemistry”