1 - Energy States of Atoms
Abstract (TL;DR):
We all know about the atom and some of us even know the three subatomic particles that make up atoms. This article talks about the atom from the standpoint of explaining why the atom behaves how it does.
The atoms communicates through the use of its electrons, which are oriented in specific ways according to their energy state. Since atoms and their electrons want to be at their lowest energy level, electrons move in ways that get them there, creating beautiful shapes called “orbitals”.
Image via nickvdg
How does one personify the relationship between an individual 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 it 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 composed of protons and neutrons, the former being positively-charged and the latter having no charge. The dance that these particles undergo will absolutely be a subject of our attention in a future arc, but, for now, let’s focus on the electron - the currency, as I’ve called it. Atoms use these electrons to communicate. 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 less painless than your instructors tried to.
In order to properly understand the atom, we have to start with a philosophy 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.
There is a problem. You would think that, if you’re an electron, the best place to be is right up against the nucleus. But electrons all have the same charges and that means that energy actually increases the closer and closer they get to each other. So, if the goal is lower energy, then what are they supposed to do so that every electron is satisfied? Well, they deal with it by organizing into different energy levels. Those levels or states are what we call orbitals, which are the paths that an electron takes according to the amount of surrounding electrons and protons within the nucleus.
There are even more reasons that explain the presence of orbitals, but we’ll go over two of the most important.
Evidence of Orbitals
The Mathematical Orbital
There is a formula out there that explains the electric force that keeps electrons apart.
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. Basically, this constant, 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.
Last is r, or the distance between the two 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 repulsion 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!
The Electron Clouds
Image via Byjus
I hate to burst bubbles (except in cases like this), but this classic image above is actually an inaccurate representation of the atom. Electrons move incredibly fast - so fast that they could appear in multiple places at once. 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
Brought to you by Schrödinger. Yes, the same one with the cat and the box. Or was there a cat in that box…?
In any event, 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.
Image by Ms. Lintan via Tumblr
High potential energy up there, high kinetic energy on his way down…And zero energy when he hits the ground…Splat.
If you were wondering why an electron just doesn’t smash into the nucleus, it is because the amount of kinetic energy is far larger than the potential energy at the center. In fact, the kinetic energy is practically infinite at the center; therefore, the momentum of the electron is infinite at the center. At that point, it’s impossible for the electron to attach to anything – it’s got far too much energy!
Wait…too much energy? We can’t have that, now can we?
To minimize net energy, there must be a certain distance where the electron is placed so that it still experiences attraction from the nucleus and does not experience a near infinite kinetic energy. This balance is tentative, causing the electron to move in an unpredictable manner, but still maintain a certain area. These are orbitals!
Orbital Chemistry
Now that we understand why they form, we can delve into them more closely in future articles. We’ll see that, according to the distance that the electrons occupy, the orbitals of the atom can look different. The electron cloud above, for example, represents the orbital configuration that one would see in a lithium atom, but we have tons more. For now, enjoy this sneak peek at what is coming next.
Image by Donald A. McQuarrie via “Quantum Chemistry”