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?
The Necessity of Negativity
The only way to properly answer that question is to explain the importance of the negatively-charged electrons.
While any atom’s core is made up of protons and neutrons, two of the most elementary particles in existence, electrons surround that core, attracted to its positively-charged protons. Yes, the phrase “likes repel and opposites attract” is certainly true of subatomic particles and is a fundamental truth of chemistry. However, I digress: electrons are also crucial in the communication between that element and any other.
Think of it this way: electrons are the invitation to the party that every particle in the universe wants to be a part of. The particles show off their ‘status’ by how many electrons they own. Kind of like the guy that doesn’t stop bragging about how many girls are into him. Yeah, we all know that guy.
The guy is a jerk, but he still gets whatever he wants because he’s got the social pull. Well, believe it or not, atoms are the same way.
You may have heard the terms “valence shell” and “orbital”. Yes, I can already hear the collective cry of pain from those who are familiar with the beginning lessons of chemistry in college or some advanced high-school programs. Don’t worry. I will make this…less painless than your professors tried to.
In order to properly understand, we have to start with a philosophy that holds true for every system in the universe. That is, that there is always a desire to be at the lowest energy possible. Everything you see in the world follows this principle. It is why when a car crashes, sound is released in response to how fast the car was going. That is an example of a transfer from kinetic energy, the energy of motion, to sound energy. Energy represents stability of a system. The lowest energy state represents the most stable state. In other words, if a system could not release energy, for whatever reason, it would be considered unstable.
Orbitals are an extension of that philosophy. These are the representation of energy states in any given element, which are “filled” by our party-invitations, the electrons.
But if an electron is randomly encircling the nucleus of an atom, why would there be different energy states? What causes electrons to occupy different orbitals?
When you are an electron, you are naturally the most attracted to the nucleus of an atom, where both positively charged particles reside. But you could imagine, if an atom with a large atomic number, or the number of protons in the nucleus, were to be surrounded by an equally large number of electrons in close proximity, you should generally expect that all of the negative charge near each other would increase the total energy of each electron – remember, likes repel, meaning electrons do not like electrons. This is according to the electric force, that very cumbersome thing that I mentioned in the first paragraph. In chemistry and physics, this is referred to as 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 other have positive electric force, meaning they repel, and their energies rise when near each other. The question, then, is what would electrons in close proximity do?
If you answered that they try to reduce their energy, you are 100% correct.
The higher the repulsion force, the more likely they are to distance themselves in order to lower that total energy. This creates a situation where electrons are not only attracted to the positively-charged nucleus, but repelled by lower-energy electrons. This fits intimately with the concept of orbitals – electrons randomly “orbiting” the nucleus at different energy states.
The Atomic Balancing Act
The quotations I put around “orbiting” are important, as electrons do not really orbit in your conventional sense. In actuality, they occupy a certain space around the nucleus and can be anywhere in that space or at any time. So, yes, if you didn’t know, that classic image of an atom founded by Ernest Rutherford is completely wrong. In actuality, it looks like this:
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 discuss energy once again. 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.
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 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?
Therefore, 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.
If you've already been dipped into the "orbital pool" (that sounds gross) and guessed that this sounds a lot like orbitals, congratulations, you’ve mastered energy states! According to the distance that the electrons occupy, the orbitals of the atom can look different. The electron cloud above represents the orbital configuration that one would see in a lithium atom…But we have tons more…Enjoy this sneak peek at what is coming next.