In the previous installment of "Mechanical Materials for Beginners," we explained the main classifications of mechanical materials.
Starting with this installment, we will begin by explaining atomic structure, the first part of our series on the theory of mechanical materials.
The content covered this time is not directly applicable to manufacturing, but rather closer to middle and high school chemistry. However, it is important to understand the fundamental concepts that determine the basic properties of materials, such as strength, toughness, and conductivity.
Many actual designers have forgotten this, but actuallyThe content presented here is extremely important, as it relates to the limiting mixing ratios of various additives (carbon, chromium, molybdenum, etc.) when alloying iron, a representative mechanical material, and to the penetration of typical surface treatments such as carburizing, nitriding, and sulfurizing.
Furthermore, it's very important because you'll also learn the meaning and interpretation of the periodic table of chemistry.
As I repeatedly mentioned in the section on mechanics of materials, it's important to note that understanding, not memorization, is crucial.
Unlike school tests, manufacturing is different.It's not about rote memorization; what's crucial is understanding the concepts so that you can apply that knowledge to manufacturing.
If you've forgotten, you can simply look it up and remember. Understanding is crucial for that very process of looking it up.
First, let's explain the structure of atoms, which are the fundamental building blocks of matter.
Atomic components (protons, neutrons, electrons)
I think most people know that the smallest unit of matter is the atom.
However, a closer examination of that atom reveals that it is composed of even smaller particles.
Its constituent materials are,There are three types of particles: protons, neutrons, and electrons.
These three substances are all interesting.They have electrical properties: protons have a positive charge, neutrons are electrically neutral, and electrons have a negative charge.
Atoms are basically composed of a number of atoms that balance the electrical energy of these substances.
Next, let's look at the weights of each constituent element. The masses of protons and neutrons are approximately $1.672 × 10^-24 g$, and the mass of an electron is approximately $1/1840$, which is roughly the same as the mass of a proton. Therefore, it is safe to assume that the weight of an atom is determined almost entirely by the weights of its protons and neutrons.
To give a concrete example, if we consider the weight of a proton to be equivalent to 1 liter of water (the equivalent of two plastic bottles), then the mass of an electron is less than that of a single drop of water.
Now, let's explain how these substances come together to form atoms.
As an example, let's explain using hydrogen (H), the first element in the periodic table and the most fundamental substance in the universe.
This hydrogen atom is basically composed of one proton and one electron.
The question is, how can we suddenly determine the number of each substance that makes up a hydrogen atom? The periodic table of chemistry plays a crucial role in this.
One of the remarkable properties of the periodic table is that the numbers for each atom tell us the number of protons and electrons that make up the substance.
This is an incredibly useful chart that shows you that a hydrogen atom (number 1) has one proton and one electron, while a helium atom (number 2) has two protons and two electrons.
Therefore, it's useful to remember the numbers of the major atoms (called atomic numbers) (but even if you forget, you can always look them up).
In this periodic table, atomsThe number of constituent elements is mostly known, but the troublesome thing is that the number of neutrons is unknown.
Basically, atoms are electrically balanced, so the number of protons and electrons is equal.
Neutrons are basically composed of the same number of particles as protons,In nature, there are occasional instances where the number of neutrons differs from the number of protons.
Such materials have the same number of protons and electrons, but different numbers of neutrons.These are called isotopes.
For example, in the case of hydrogen, a hydrogen atom with one proton and one electron, which makes up more than 99% of the hydrogen naturally, is called light hydrogen (simply hydrogen).
Hydrogen isotopes consisting of one proton, one neutron, and one electron are called deuterium, while hydrogen isotopes consisting of one proton, two neutrons, and one electron are called tritium.
Many atoms have isotopes like this, but since this course is about mechanical materials, I'll stop the explanation here (I only know the well-known ones myself).
For reference, I think many people already know this, but there's a convenient number to represent the number of neutrons.That is called the mass number.
The concept of mass number is extremely simple: it's the sum of the number of protons and neutrons.
In essence, as explained, the weight of an atom is largely determined by the number of protons and neutrons, so the mass number is called the "mass number" because "the sum of the number of protons and neutrons is approximately equal to the mass."
This method of expressing mass numbers is illustrated in the following diagram, using hydrogen as an example.
Then the table of hydrogen isotopes is completed and represented as follows.
Incidentally, this tritium is a type of tritium that has recently been causing a stir.
Tritium is an unstable substance that is rarely found in nature, but it is produced as part of nuclear energy reactions, such as those in nuclear power plants. This tritium is very unstable and tries to become the relatively stable deuterium by undergoing beta decay, which eliminates the neutrons (nature tends to move towards stability).
If those decaying neutrons simply decayed on their own, there wouldn't be a problem, but along with the decay they release a troublesome substance called radioactivity (the neutrons disappear, transforming into radioactive material).
Its half-life is a bit short at about 12.3 years, so it emits radioactivity at a moderate rate.
Well, the amount of radioactivity emitted from a very small amount of tritium is not a problem at all, but when a large amount of tritium gathers and emits radioactivity, it becomes difficult to say that there will be absolutely no impact on society or the natural world.
I think the dangers of high levels of radiation need no introduction here.
That concludes the explanation of the individual substances that make up an atom. Next, we will explain the structure of the atom.
Atomic structure (electron orbitals, electron shells)
I find the structure of this atom incredibly interesting and fascinating, so I will try to explain it as clearly as possible.
First, the arrangement of protons, neutrons, and electrons, which are the constituent elements of each substance, can be illustrated as follows, using hydrogen and helium as examples.
Basically, it has a structure where a proton and a neutron are bound together, and electrons orbit around them.
このThe part where protons and neutrons are attached is called the atomic nucleus.
I remember being deeply moved by this at the time, as it felt similar to the relationship between a planet and its moon.
I imagined that there might be a relationship within atoms similar to that between the Earth and the Moon.
However, the actual distances are quite different; the Earth and the Moon are relatively close, while the atomic nucleus and electrons are much farther apart.
However, when I was a student, I was taught that electrons orbit the atomic nucleus in a circular path, but according to the latest chemistry, electrons do not move in a regular circular motion, but rather move somewhat randomly.
Therefore, technically, it seems incorrect to use the word "orbit," but it's apparently acceptable to still call it an orbit due to academic convention (similar to how the flow of electricity and the movement of electrons are inversely related).
Up to this point, we have explained using hydrogen, which has one electron, but as the number of electrons increases, it becomes as follows (for example, helium, which has atomic number 2).
As shown in the diagram, this structure results in two electrons occupying the same orbital.
So, if the number of electrons continues to increase, will the increased electrons simply occupy the same orbitals? The answer is no.
The number of electrons that can occupy a single orbital is determined by a certain constant.
So where do the electrons that couldn't fit go? They create new orbits outside the full orbits and move into those.
In this way, electrons enter orbitals, and any excess electrons create new orbitals outside and enter them, and this process repeats.
These orbitals also have names, and are called the K shell, L shell, M shell, N shell, and so on, in order of proximity to the atomic nucleus.
It was a mystery why it started with K, the alphabetical letter, but upon investigation, it was initially thought that there were orbits further inside, so they named them starting with K, the 10th letter of the alphabet, just in case. However, subsequent investigations revealed that there were no orbits further inside, so the rule of starting with K continues to this day.
Such inappropriate naming conventions are common in the worlds of academia and engineering.
If any readers make a new discovery and name it in the future, please be careful when naming it, as the name may be used long after you are gone.
I haven't made any groundbreaking discoveries myself, but I have given arbitrary names to parts of new mechanisms and later regretted it (like the KAZUBARA link).
To get back to the main point, the number of electrons that can be placed in each orbit is fixed: 2 in the K shell, 8 in the L shell, 18 in the M shell, and 32 in the N shell.
The number of electrons here isBasically, the nth electron shell can hold 2n^2 electrons.
The question that everyone will naturally wonder at this point is, "Why is the number of electrons that can fit into each electron shell fixed? Or is it different?"
I thought the same thing when I learned it, but my teacher at the time just said, "I don't know, it's the rule."
Further research suggests that understanding quantum mechanics might explain the reason for the number of electrons that can be placed inside, but even now, the exact reason is still unknown, and it seems to be some kind of approximation.
Let's look at some diagrams illustrating the different structures that result from increasing electron counts. We'll start with magnesium and aluminum, which are frequently used in mechanical materials.
I remember being deeply moved by this situation when I first learned about it, as it reminded me of the relationship between the planets around the sun.
In reality, it's important to note that the regular laws, motions, orbits (such as Kepler's laws), and sense of distance in interstellar space are different from the laws within atoms.
In general, electrons fill the inner orbitals first, creating new orbitals on the outer shell in sequence. However, this rule only applies up to the eighth electron in the M shell; from then on, electrons skip the M shell and go directly into the N shell.
Apparently, electrons like the number 8, and an orbital becomes stable when there are 8 electrons.
thisThis is called the Octed Law because the number 8 is called an octet.
To make it easier to understand, imagine each shell as a train car.
First, the K section of the train car closest to the platform exit has about two seats, which is convenient, so people fill it up until it's full (up to two people, so competition is high).
Next, the L-shaped car closest to the platform exit has about 8 seats and is fairly convenient, so sit there until it's full (up to 8 people).
Next, in the M section of the train car closest to the platform exit, there are about 18 seats, but it's not that convenient, so only 8 seats are ever occupied.
The remaining people (electrons) find that there isn't much difference in convenience between the M-shell and N-shell cars, which are farther from the platform exit, so they think it's better to go to the N-shell car, which is less crowded and more comfortable.
Nature has a law of nature that dictates it should take the easy way out, which sometimes makes its actions resemble those of a lazy person (I, the author, am extremely lazy).
This law can be applied up to the third period of the periodic table, but it seems to behave differently beyond that.
Based on what we've learned so far, within an atom, there is a nucleus at the center, with electrons surrounding it. When you look at an atom with an electron microscope, it seems that many atoms are moving at high speed according to a specific set of rules, making it look like a cloud (I have seen this in photographs).
Because it looks like a cloud, it is called an electron cloud.
A simple analogy would be a galactic nebula, where countless stars gather around a black hole (supergravity).
It's truly awe-inspiring to see images similar to those of supermassive galaxies within the smallest matter in the universe.
The explanation so far describes the relationship between electrons and electron orbitals.
Electron behavior (ionic state)
From here, we will explain the behavior of electrons.
From the explanation so far, each substance that makes up an atom will have the same number of protons and electrons so that it is electrically balanced,There is a state in which electrons become more stable than that electrical balance.
That isElectrons prefer to have all their electron orbitals filled to capacity.
These extremely stable types of atoms are called noble gases, and you can easily identify them by looking them up in the periodic table. The rightmost vertical column consists entirely of noble gases.
However, in the M shell, according to Octed's Law, once eight electrons have entered, electrons will move into the next N shell.
Apparently, electrons find it easier to sit in the next N shell's seat than in the ninth seat of the M shell, so they skip over (natural phenomena generally favor the easier option).
In other words, electrons areSometimes, an atom prioritizes a state where its electron orbitals are full over a state of electrical equilibrium; this state is called a closed shell.
So, how do electrons try to close their shells?If an electron shell is short by 1 to 3 electrons, it will try to fill the gap with electrons from outside. If it has 1 to 3 extra electrons compared to a full shell, it will try to release them.
This behavior causes atoms to gain or give electrons from other atoms, thereby closing their shells.
In this closed-shell state, the atom, which originally had the same number of protons and electrons and was electrically balanced, can gain or lose electrons.The electrical balance is disrupted.
このThis state is called an ionic state.
To explain in more detailWhen a proton receives electrons from elsewhere to fill its shell, which was previously insufficient, the number of electrons becomes greater than the number of protons, resulting in a positive electrical state.
This state is called a positive ion, positive ion, or + ion.
Conversely, for closed shellsSince there are extra electrons, if they are released to fill the shell, the number of electrons will be less than the number of protons, resulting in a negative electrical state.
This state is called an anion, negative ion, or -ion.
Whether each atom becomes a positive or negative ion is easier to understand if you consider it based on the principle that "nature acts in the direction that is easier."
For example, if the M shell, which is stable with 8 electrons, is short 1 to 3 electrons, it is easier to get electrons from elsewhere, so it becomes positive. If there are 1 to 3 extra electrons in the L shell, the electrons are released, so it becomes negative.
In other words, it acts on the side with fewer moving electrons (for example, if there are 8 electrons, less than 4 would be a good guideline).
周期表を使うとどんなイオンになりやすいかすぐにわかる。原子番号が近い希ガスに対して原子番号が1大きければ＋、2なら2＋、3なら3＋となり逆に原子番号が1小さければ1ー、2なら2ー、3なら3ーとなることが多い。
The ionic state of an atom is a crucial state of matter that greatly influences various reactions, including bonding, which we will explain later, so please make sure you understand it well.
Also thisThe ease with which atoms become ions differs from atom to atom, and the order in which atoms are most likely to become ions is called the ionization tendency.
I will explain the details later, but thisIonization tendency is extremely important for mechanical materials and serves as a crucial indicator of the occurrence of galvanic corrosion (rust caused by the galvanic action of dissimilar metals), a type of corrosion.
Even today, serious defects and accidents can occur due to overlooking the possibility of galvanic corrosion, so please at least remember the keyword.
This concludes the explanation of atomic structure.
On a different note, I don't really understand how negative ions, which have been popular for over 10 years, are supposed to have a positive effect on the human body.
Negative ions are a term that describes the state of matter, not a term that describes a physical phenomenon, physical action, or chemical reaction. Nothing happens simply by the presence of negative ions.
Furthermore, various substances can enter a negative ion state, so which substance's negative ion state is being referred to when we talk about negative ions?
I would like someone to explain this to the author.
Summary
Now let's summarize the structure of atoms.
Atoms are composed of protons, neutrons, and electrons.
The number of protons and electrons in an atom is basically the same, and the number follows the atomic number in the periodic table.
While atoms generally have the same number of neutrons as protons, isotopes (isotopes) with different numbers of neutrons exist in nature.
The structure of an atom consists of a nucleus made up of protons and neutrons, with electrons surrounding it.
The orbits around the atomic nucleus in which electrons can exist are called electron shells, and the number of electrons that can occupy an electron shell is fixed.
Electron shells are called K, L, M, N, etc., in order from closest to the nucleus, and the number of electrons they can hold is 2, 8, 18, and 32 respectively, with the nth shell holding $2n^2$ electrons.
Electrons are most stable when their electron shells are full (closed shell), and they attempt to exchange electrons with the outside world in order to fill their electron shells.
- When electrons are exchanged to close the shell, the electrical balance within the atom is disrupted. This state is called an ionic state, and a state with more electrons than protons is called a positive ion, while a state with fewer electrons is called a negative ion.
Becomes
This has turned out to be a bit long, and most of the content is from middle and high school chemistry, but it's important, so I really hope you'll understand it.
Unfortunately, the content presented here will have very little direct use in manufacturing or work, including mechanical design.
However, when trying to create something new or when dealing with unprecedented phenomena or events that occur during work, it becomes almost impossible to move forward without understanding the fundamentals like those discussed here.
This is the author's wish, but if possible...This book explains the fundamentals of science with the hope that many people will become engineers who can imagine and discover new things, rather than just engineers who do routine work.
Next time, building on what we've covered today, we'll introduce interatomic and intermolecular bonds.
If you're interested in this field, I think you'll find it even more interesting if you study quantum mechanics.
What was once thought to be the smallest unit of matter was the atom has evolved over time to protons, and upon closer examination, it has been discovered that protons are composed of quarks, showing that matter is becoming increasingly smaller and smaller.
Currently, the smallest particles are quarks, but it's unknown what will be discovered in the future.
Science merely systematically compiles what we currently know; it does not explain the mysteries of the universe.I want you to be interested.
In other words, things that science doesn't understand aren't necessarily wrong or impossible; they simply haven't been sufficiently verified, experimented with, or proven yet.
Especially when you try something new, you'll encounter all sorts of phenomena you've never seen before and experimental results that make no sense.
Having such experiences makes me strongly feel that modern human science and technology are still a long way from being able to explain everything in the universe.
To those who found this article helpful in understanding design:
While there is basically no textbook covering this content, and it is my own original work, I will introduce the textbook that I have been using since I was a student.
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