Nuclear Reactions

Through the previous articles we have pieced together the purpose of each component of the atom (protons, neutrons, and electrons) and we saw what happens when we move these particles around. Electrons are exchanged between atoms causing new bonds to form during chemical reactions. Nuclear reactions occur when there isn't a proper balance of neutrons and protons in the nucleus. We saw that in some cases, neutrons and protons will transform into each other if doing so would put the nucleus in a much lower energy state.

So what exactly does it mean to be "in a lower energy state"? When something moves from a high energy state to a lower energy state, it gives off energy. On the other hand, if you want to move something from a low energy state into a higher energy state, you have to put energy into it. The lower an energy state something is in, the more energy it will take to get it back up to a higher energy state.

Changes of Energy State

For example think of a big rock sitting halfway up a hill. It will take a lot of energy to roll the rock from the halfway point to the top of the hill, but it will take much more energy if we start all the way at the bottom. Note also the the rock will naturally want to roll to the bottom if you give it a push. In this case the top of the hill is the highest available energy state and the bottom of the hill the lowest with respect to the Earth's gravitational field.

Don't try this at home

For the protons and neutrons in a nucleus the tighter they are bonded, the lower the energy state of that system and the more energy it would require to take them apart. Now obviously it takes more energy to disassemble larger nucleii than smaller ones simply because there are more nucleons. A big wall made of many bricks will take more energy to disassemble than a smaller wall made of fewer bricks, but that doesn't mean that the bricks in the larger wall are more strongly stuck together than those in the smaller wall. A better comparison would be the total energy to take apart the wall divided by the total number of bricks if we really want to know how strongly the bricks are stuck together.

Unless you have dynamite in which case it doesn't really matter how many bricks there are

In order to compare how tightly bonded two nucleii are, we use the total energy needed to disassemble it divided by the total number of protons and neutrons. This gives us the average binding energy per nucleon and we can use it to better compare how tightly bound different nucleii are. The lower the energy state of a nucleus, the more energy it takes to pull it apart and the higher its binding energy per nucleon will be. If this sounds counter-intuitive, think back to the rock. The lower the energy state of the rock, the more energy you need to use to get it up the hill.

Binding Energy Per Nucleon of Various Isotopes

The graph above shows the average binding energy per nucleon of various isotopes. The lightest ones are on the far left and include hydrogen (H), helium (He), lithium (Li), etc. These are the elements at the top of the periodic table. On the right side are the heaviest ones such as uranium (U) which are near the bottom of the periodic table. The atom with the highest binding energy per nucleon is nickel, specifically nickel-62 (Ni-62), closely followed by iron-56 (Fe-56). These two isotopes have the most tightly bound nucleii of all and, as you may have guessed, sit near the middle of the periodic table. Note that nickel is element number 28 and iron is element number 26 if you're trying to find them on the periodic table. The number "62" in Ni-62 and "56" in Fe-56 is the total number of nucleons (protons plus neutrons).

Image courtesy of Wikimedia Commons

Ok so we've established that nucleii will try to put themselves in lower energy states which means creating tighter bonds between their protons and neutrons. We also know that it isn't the lightest elements (like hydrogen) nor the heaviest elements (like uranium) that are the most tightly bound. The ones in the middle (like iron and nickel) have the most tightly bound nucleii and are therefore at the lowest energy state of all the isotopes. In general, nuclear reactions involving heavy isotopes will result in them becoming lighter and reactions involving lighter isotopes will result in them becoming heavier. Both want to end up somewhere in the middle near iron-56 and nickel-62 because this is the lowest energy state. The question then becomes, are all the isotopes slowly turning into iron and nickel?

To answer this let's go back to the rock on the hill. If you let a rock go it will roll downhill, no surprises there. However anyone who's ever tried this in practice knows that the rock rarely makes it all the way to the bottom without being snagged and stopped by something. There are small local low energy states on the way down that the rock can get caught in and stay indefinitely.

Rock becomes trapped in a small hole and isn't able to escape without a push

Things cannot move from low energy to high energy unless you add energy to them so once the rock gets caught in a local low energy state, it will stay there forever until someone or something gives it enough of a push to escape and continue rolling down the hill. The same is true of nuclear reactions, a nucleus will try to re-arrange itself to move towards the lowest energy state but if it happens to put itself into a stable state along the way, it will stay there. We can see this on the chart of the nuclides, all the black squares are stable nucleii. The coloured ones are unstable (radioactive) and will slowly change until they eventually become one of the stable (black) nucleii. Some will eventually become iron or nickel if they are already close but the ones that are further away will likely become some other stable isotope.

Of all the possible combinations of neutrons and protons, only a few are stable

We know that nucleii can convert neutrons into protons and vice-versa to move towards stability but there are some more spectacular reactions available as well. Some really heavy nucleii will actually split themselves to become two smaller nucleii, releasing a lot of energy. This is called nuclear fission and is how nuclear reactors are able to produce power. On the other hand, really light nucleii if they are under enough pressure or given enough energy can actually stick or fuse together into heavier nucleii, also releasing a lot of energy. This is called nuclear fusion and is how stars produce their energy. They both result in a release of energy because the nucleii end up moving into a lower energy state after the reaction.

Nuclear reactions typically result in more tightly bound nucleii

So there you have it, nuclear reactions are the result of nucleii trying to move towards a more tightly bound nucleus (lower energy state). This causes nucleii much larger than iron and nickel to typically become smaller and nucleii smaller than iron and nickel to typically become larger. Although they are trying to get to the lowest possible energy state, unstable (radioactive) nucleii will typically end up becoming one of the many stable nucleii along the way and stay there.

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The Not So Useless Neutron

We now know that electrons are responsible for the reactions we see in everyday life whether they be rusting, burning, rotting, etc. In The Alchemist's Dream we saw that the reason alchemists were never able to create gold from regular metals was because they were only able to cause chemical reactions to occur. The atoms themselves never change during a chemical reaction, they simply exchange electrons and bond in different ways.

It wasn't until the discovery of radioactive elements and the invention of particle accelerators that we were able to witness and control nuclear reactions in the lab. Nuclear reactions involve changes to the nucleus of an atom. Since it is the nucleus that uniquely defines the type of atom, being able to change the nucleus opens up the possibility of converting one type of atom into another.

To better understand what's going on in the nucleus, let's have a closer look at the two particles that make it up: neutrons and protons. Recall that protons are positively charged and neutrons have no charge. The number of protons in a nucleus is what defines what type of atom it is. For example atoms with 3 protons are lithium atoms. Interestingly enough, the number of neutrons is not always the same for a given atom. For example lithium atoms can be found in nature which have either 3 or 4 neutrons (4 being the most common). Atoms of the same element with different numbers of neutrons are called isotopes. This brings us to two very important questions:

1. What purpose do the neutrons serve?
2. Does it matter how many neutrons an atom has?

To answer this, let's start by having a look at the nucleus of a lithium atom, in this case we'll look at the isotope with 4 neutrons. Lithium with 4 neutrons is referred to as Li-7. "Li" is the chemical symbol for lithium and the "7" shows the total number of particles (also called nucleons) in the nucleus (3 protons + 4 neutrons = 7 particles in total). The isotope with 3 neutrons as you may have guessed is called Li-6.

Nucleus of a Lithium-7 Atom

To understand the purpose of the neutrons, take a really close look at the image above. Something doesn't quite make sense...

Any kid who has ever played with magnets knows that opposite charges attract and like charges repel. If that's the case, then how can all these positively charged protons stay stuck together in the nucleus? Their electrical charges should cause them to push each other away, however there are other forces at play here. Although it may seem like there are all kinds of different forces we encounter in our world, there are actually only 4:

1. Gravity

2. Electromagnetism

3. Weak Nuclear Force

4. Strong Nuclear Force

Gravity is something we're all familiar with, electromagnetism is also familiar to us through magnets, electricity, lightning etc, the weak nuclear force involves forms of radioactive decay that we won't discuss here, and the strong nuclear force is what binds particles in the nucleus of an atom together.

The strong nuclear force is, as the name suggests, very strong but it can only act over very short distances. It is responsible for holding together the quarks that make up protons and neutrons (we discussed this briefly in The Indivisible(?) Atom). A side effect of this is that it also causes the quarks in different protons and neutrons to attract each other. Without getting into too much detail, the strong force causes protons to attract both other protons and neutrons and causes neutrons to attract both other neutrons and protons but only when these particles are very close together. If you want to get into more detail, the field studying these effects is called quantum chromodynamics.

A name which is almost as hard to understand as the subject itself

The reason all the positively charged protons in the nucleus don't push each other apart is due to the strong force. Once they are close enough together, the strong force pulling the protons together overwhelms the repulsive force due to their like charges. Since the strong force applies to both neutrons and protons, the neutrons play just as much a role in holding the nucleus together as the protons do. So now we know their purpose: to help hold the nucleus together. However we still haven't answered the question of whether or not it matters how many neutrons there are in the nucleus. In fact we've backtracked a bit because this raises a third question:

3. Does more neutrons mean a more strongly bonded nucleus?

The protons stick together due to the strong force but their positive charges are still trying to push them apart a little bit. The neutrons also stick to each other and to the protons but they have no charge so they don't push apart. It therefore wouldn't be unreasonable to assume more of them means a stronger nucleus right?

As usual, truth is stranger than fiction. If you read What Is Chemistry?, you will recall that electrons organize themselves into "clouds" or "shells" and they fill these shells in a specific order from inside to outside. The protons and neutrons organize themselves in a similar way within the nucleus. As you add protons to a nucleus, they will gradually fill the different shells available. The same is true for neutrons but they do this independently of the protons. In other words, neutrons will not fill proton shells and protons will not fill neutron shells.

Shells are essentially a way of saying different energy levels. Different positions within the nucleus will result in a proton or neutron achieving a different energy level. Just like a ball falling from a table to reach a lower energy state within the Earth's gravitational field, a proton or neutron will "fall" into a lower energy state within the nucleus if it has the chance. As I said before, protons and neutrons each have their own energy levels or shells within the nucleus, however something very interesting will happen when the number of neutrons and protons is not properly balanced.

Let's take a look at our Lithium-7 atom again, but this time we'll add an extra neutron to see what happens:

Adding an Extra Neutron to Li-7

Once we add the neutron, it must position itself in a higher energy spot than the neutrons already there. You'll notice though that there's a really nice low energy proton position just begging to be filled. If the difference between the highest available neutron energy level and lowest available proton energy level is large enough, something remarkable will happen:

Decay of Li-8 Into Be-8

As you may have guessed, the neutron will transform itself into a proton and move into the lower energy level. In doing so it will release an electron (which we're familiar with) and an electron antineutrino (which is a more exotic particle that we won't discuss here). The resulting nucleus will now have one extra proton but the same total number of nucleons (4 protons + 4 neutrons = 8 particles in total). An atom with 4 protons is called Beryllium so this new isotope is called Beryllium-8.

For atoms with a high number of protons but relatively few neutrons, a proton can also transform into a neutron. Neutrons and protons will transform into each other only if it puts them into a low enough energy state to justify the transformation. Nucleii who could lower their overall energy by making such a transformation are called radioactive. The name comes from the fact that these transformations release radiation. Once a nucleus achieves an energy state that it cannot reduce, it is called stable. It turns out that of all the possible combinations of neutrons and protons, there are very few that are actually stable. You can see this on the chart of the nuclides below. The stable nucleii are in black, the rest of them are radioactive.

Chart of the Nuclides

The chart shows all the possible isotope combinations. The number of neutrons is plotted along the x-axis and number of protons along the y-axis. For the most part, the stable nucleii have about the same number of neutrons and protons. However you'll notice the line of black bends down a bit as you move up the graph.This is because in larger nucleii, most of the protons are too far apart to be attracted to each other by the strong force. It therefore takes more neutrons to overcome the repulsion of these distant protons.

Now we finally have the answer to both our original questions plus the third question that we came across while trying to answer the first two:

1. What is the purpose of the neutrons? 

The strong force applies to neutrons and protons, causing them to attract each other so neutrons help hold the nucleus together.

2. Does it matter how many neutrons there are?

Absolutely. Neutrons and protons both have energy levels within the nucleus. If there is too many of one or the other, a transformation will occur to achieve a stable balance.

3. Do more neutrons mean a more strongly bonded nucleus?

Yes and no. If there are too many neutrons then a neutron will typically transform into a proton to put itself and the nucleus into a lower energy state. For small atoms, a stable nucleus has about the same number of neutrons and protons. However larger nucleii require some extra neutrons to compensate for the fact that there are so many protons trying to push each other apart. The most stable mix of neutrons and protons in a heavy nucleus will therefore be when there are a few more neutrons than protons.

I will close by saying that we discussed two types of nuclear reactions here: transformation of neutrons into protons and transformation of protons into neutrons. As it turns out, there are other reactions that nucleii can use to achieve stability. These other reactions hold the secret to how stars shine and how nuclear power plants make electricity.

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The Alchemist's Dream

In the previous post we saw that chemistry is simply the movement of electrons between atoms. The sheer number of different types of atoms and ways in which they can exchange electrons is the reason chemistry is such a complex and diverse field of science.

Electrons, as you may recall, surround the nucleus (without touching it) in what is called an electron cloud. Although the exchange of electrons during chemical reactions will affect the electron clouds around the nucleus, the nucleus itself remains unaffected. In other words even the most violent of chemical reactions will have no effect on the protons and neutrons in an atom.

Let's forget everything we know about atoms for a moment and step back in time. If you've ever heard of the term "alchemy" before, you probably associate it with ancient mad scientist types trying ruthlessly to figure out a way to convert regular metals into gold. This was supposed to be possible by mixing them with a substance known as the "philosopher's stone" but was never successfully done. Towards the 18th century, the field of alchemy was surpassed and replaced by its offshoot: chemistry. Alchemy took a more philosophical/mystical approach, while chemistry was based on testing hypotheses against the results of repeatable experiments. It was this approach that led to the discovery of the elements as well as the atom and its constituents (which we discussed in The Indivisible(?) Atom).

Image courtesy of Wikimedia Commons

Recall for a second the goal of alchemy: the conversion of regular metals into gold. After centuries of trial and error, why didn't anyone succeed in making the transformation? It's true that alchemy was less robust than chemistry but alchemists still managed to figure out how to extract metals from rock and mix them into alloys like bronze. Even cavemen and cavewomen were able to produce the chemical reaction known as fire without any chemistry knowledge. You would think that someone over the centuries would have accidentally had the luck of creating gold from regular metals. That is of course, assuming it's actually possible. This is where chemistry enters into the picture, let's have a look at the periodic table.

Image courtesy of Wikimedia Commons

We can see that Gold (symbol Au) is an element with atomic number 79 (located near the centre of the table). The fact that it's an element is important because that means it cannot be made by mixing other substances. Gold is one of the fundamental types of atoms that make up our universe. It happens to have 79 protons and, when neutrally charged, 79 electrons as well. We saw at the beginning of the article that chemical reactions affect only the electrons around atoms. The nucleus, including all the protons and neutrons within it, remains unaffected. It is therefore impossible to create gold from any chemical reaction. No wonder nobody was ever able to do it.

The fact that the atoms themselves are not affected by chemical reactions was a powerful discovery. Early chemists like Antoine Lavoisier were able to figure this out by carefully capturing all byproducts of reactions and weighing them. They found that they always weighed the same as the initial reactants. Lavoisier through his own experiments and the careful review of others was able to show that water, long though to be an element, was in fact made up of hydrogen and oxygen. He deduced that water could be separated into hydrogen and oxygen and that they could be recombined again into water. "Nothing is created, nothing is destroyed, everything is transformed" as he put it.

Unfortunately he also collected taxes for the king and was executed during the French Revolution

So there you have it, atoms themselves do not change during a chemical reaction, they simply re-arrange themselves to form new compounds. This idea remained a cornerstone of chemistry for about 200 years. However this long-held belief was shaken in 1902 by Ernest Rutherford and Frederick Soddy while they were studying the radioactive element thorium (symbol Th, number 90 on the periodic table). The two noted that their thorium sample was spontaneously producing helium, among other substances. Conventional wisdom suggested this should not be possible. How could one element (thorium), be creating another element (helium)? They concluded that radioactivity is the result of atoms spontaneously decaying into other atoms. So much for atoms never changing!

Although the idea was ground-breaking, it is still true that in a chemical reaction the atoms themselves do not change, they simply exchange electrons and recombine. Reactions which involve atoms decaying into other atoms (also known as transmutation) are called nuclear reactions because they are the result of changes in the nucleus of an atom. These changes happen when the nucleus is unstable and can be induced artificially in the lab. Rutherford first demonstrated this in 1919 by transmutating nitrogen into oxygen.

So if nitrogen can be transmutated into oxygen, is it really possible after all to realize the alchemist's dream of creating gold out of regular metals? The answer is yes, in fact this was demonstrated by Glenn Seaborg in 1980 starting with the metal bismuth (atomic number 83 on the periodic table). However it required the use of a sophisticated particle accelerator, something no alchemist could have gotten their hands on. Alchemists were limited to using chemical reactions only and therefore had no hope of ever producing gold. Trasmutating one atom into another requires a nuclear reaction, something we will discuss further in the next article.

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What is Chemistry?

In a previous article, I discussed the structure of the atom and mentioned that it contains positively charged protons and neutrally charged neutrons in the nucleus, and negatively charged electrons forming a "cloud" around the outside. Below is a helium atom as an example.

Despite the fact that electrons are many times smaller than protons, their charge is of the same magnitude. That is to say that the amount of negative charge on one electron is exactly equal to the amount of positive charge on one proton. An atom therefore needs an equal number of protons and electrons to have a neutral charge (in the case of Helium, this works out to 2 protons and 2 electrons). Whenever the number of protons and electrons are not balanced, the atom is called an ion.

At this point I would like to elaborate a bit on exactly what I mean by electron "cloud". In the early days it was thought that electrons circle around the nucleus in orbits called "orbitals". It seemed to make sense at the time that each atom must look like a little solar system with the nucleus playing the role of the sun and electrons the role of planets. As elegant as this sounds, the real answer turned out to be much more strange. 

Whenever charged particles change direction or speed, they give off a little energy in the form of electromagnetic radiation. This law of nature is the reason radio towers can send music to your car radio receiver and why power stations can produce electricity from spinning turbines. If electrons were truly orbiting around the nucleus, as they turn they should constantly emit some electromagnetic radiation and in doing so lose some energy. This constant loss of energy should cause the electrons to spiral ever closer and eventually crash into the nucleus meaning that atoms would only be stable for a fraction of a second. Scientists couldn't help but notice that all the atoms in the universe don't seem to be spontaneously destroying themselves so it was back to the drawing board on the structure of the atom.

The solution to this problem required an entirely new branch of physics known as quantum mechanics, which is a study of motion on a very small scale. We will discuss quantum mechanics in a different article but it suffices to say that the solution to the problem is that electrons do not orbit at all, instead they exist around the nucleus in a sort of probability cloud. There are several different types of electron "clouds" (also referred to as "shells"). Each has a different shape and is capable of holding a different number of electrons.

Let's return to the periodic table of the elements for a moment (see the previous article The Indivisible(?) Atom for further details on the periodic table). We can use the table to instantly find the number of electrons needed for any given atom to have a neutral charge. Recall that the numbers given below are the number of positively charged protons in the nucleus of that atom. For example carbon (symbol "C") has 6 and argon (symbol "Ar") has 18. boron would therefore need 6 electrons to be neutral and argon would need 18. 

Image courtesy of Wikimedia Commons

We can also use the periodic table to determine how the electrons will organize themselves into various types of electron clouds. These clouds will fill with electrons starting from the inside (close to the nucleus) and moving outwards. Interestingly enough, most of the chemical behaviour of an element depends only on the number of electrons in its outermost cloud. These electrons are referred to as valence electrons. You can get a sense of how many valence electrons an element has by its position on the table. The elements in the far left row have one valence electron and the elements on the far right have a full outer cloud. So sodium (Na) has one valence electron and helium (He) has a full outer cloud. The elements in the second row from the right are one electron away from having a full outer cloud. chlorine (Cl) is an example of this.

So what does it matter whether the outer cloud is full or not? As it turns out, atoms will exchange electrons with other atoms in order to achieve an outer cloud that is either full or empty. For example sodium (Na) will readily give up its only valence electron to a chlorine (Cl) atom. Sodium empties its outermost cloud and chlorine fills its outermost cloud so its a good deal for both atoms. The result is a positively charged sodium atom (since it lost a negative electron) and a negatively charged chlorine atom (since it gained a negative electron). The two opposing charges attract and the two atoms stick together forming sodium chloride (which you may recognize as the chemical formula for good ol' table salt). I should note that this reaction is incredibly violent and yet the result is a chemical that is safe enough to sprinkle on your fries.

Image by Petr Kratochvil

Great, now what's the chemical formula for some ketchup?

So why exactly do atoms care whether their outermost clouds are filled? They don't. It is often taught in introductory chemistry classes that atoms are "striving" to fill their outer clouds as if atoms are some sort of sentient beings trying to keep up with their neighbouring atomic Joneses. The reason an electron will move from the sodium atom to the chlorine atom when the two pass close enough is because the result is a lower energy state. Admittedly this isn't a very satisfying answer at first glance so let's look at an example.

Think of a ball sitting on a table. If undisturbed the ball will stay put. If you give it enough of a bump however, it will roll off the table onto the floor and stay there. If you bump it again, it will not hop back up onto the table because in the gravitational field of the Earth, the floor is a lower energy state than the higher table. Once it moves to a lower energy state, it takes a significant amount of energy to reverse the change (in this case you would have to pick the ball up to put it back). The outermost electron in a sodium atom is in the same situation. It's sitting there just fine, however if that sodium atom bumps into a chlorine atom, the electron will "fall" away from the sodium electron cloud towards the lower energy state in the chlorine electron cloud. One the electron has been transferred, it would take a lot of energy to move it back.

Image courtesy of photos-public-domain.com

Uhh... a little help?

We've spent a lot of time discussing the electron clouds and transfer of electrons between these clouds, but what does all this have to do with chemistry? The answer is: everything! The movement of electrons between atoms is chemistry. When you see a firework explode, there is a rapid reaction taking place between oxygen and other chemicals that generates a lot of gas and heat in a very short time. The heat creates bright light and the rapidly expanding gases make a loud BANG! What about the old vinegar and baking soda trick? The atoms in vinegar (acetic acid) and those in baking soda (sodium bicarbonate) bump into one another and the electrons flow towards lower energy states. This results in the atoms recombining to form salt, water, and carbon dioxide which quickly bubbles out of the mixture. Every reaction you see in daily life, whether it be cooking food to improve its taste or watching metal rust, is the result of electrons moving between atoms. The sheer number of different types of atoms and the limitless number of ways they can be combined are the reason that chemistry is such a massive and complex field of science. And yet behind all this complexity is the simple movement of electrons from higher to lower energy states.

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The Indivisible(?) Atom

What if you were to cut the computer or handheld device you are reading this on in half. Then cut those pieces in half, and those pieces in half, and so on. Would you ever get to a point where this was no longer possible? Is there a building block so fundamentally small that it cannot be divided into smaller pieces?

This question has been asked since ancient times, in fact the word atomos was first coined by Leucippus sometime between 400-500 BCE. Leucippus, like many in his time, was a philosopher and was trying to one-up another philosopher named Zeno. Zeno had come up with the rather mindblowing idea that all motion must be an illusion. He reasoned that in order to walk across a room you must first cross half that room. But in order to cross half the distance across the room, you must first cross half that distance too and so on. Because you can divide the distance between any two points into an unlimited number of halves, there must be an infinite number of points. Since crossing an infinite number of points is impossible, all motion must be an illusion.

My mind hasn't been this blown since I saw Inception

Leucippus clearly didn't buy into Zeno's idea and proposed the following clever counterargument. It is impossible to divide a given distance into an infinite number of points because eventually you would reach some sort of fundamental building block that cannot be divided further. He called these building blocks "atomoi" meaning "indivisible". Leucippus passed his ideas onto his students and one of them named Democritus took it even further. Democrites claimed that atomoi each have different shapes which allow them to hook together an various ways. He said that the atomoi themselves never change, they simply recombine in different ways to make different materials.

The ideas of Leucippus and Democrites were surprisingly ahead of their time considering it wouldn't be until the year 1800 before the first atomic theory would be proposed by John Dalton. They were correct that atoms were the building blocks of matter and that the atoms themselves never change, they simply combine in different ways. A substance which is only made of a single type of atom is referred to as an element, and a substance made of two or more different types of atoms combined is called a compound. There are about 98 naturally occuring elements but upwards of 118 have been either already been synthesized in labs or probably will be in the near future.

Image courtesy of Wikimedia Commons

You probably remember the periodic table from high school chemistry (or possibly from your nightmares depending on how much you like chemistry). This chart quite literally contains all the building blocks required to make everything around you including yourself. In fact there's a good chance that nearly all of the 98 naturally occuring elements are somewhere in your body right now, if only in trace amounts. Just like Democrites said, atoms can combine with other atoms to make compounds, however the atoms themselves never change.

Ironically, despite being correct about the existence of atoms and their ability to combine to form compounds, Leucippus and Democritus were actually wrong about the most important part of their arguement. Atoms, a.k.a "indivisibles", can actually be divided!

So was Zeno right? Are there really an infinite number of points between any distance? Should I post the moving green stick man picture again with a clever caption? As it turns out, the atom is made up of three smaller particles: positively charged protons, negatively charged electrons, and neutrally charged neutrons. The protons and neutrons bond together in the nucleus of the atom and the electrons stay around the outside forming a so-called "electron cloud". An atom can be identified by the number of protons in its nucleus (this is the number it is given on the periodic table). The number of protons will determine the number of electrons needed to make a neutrally charged atom. In other words you need 2 electrons to have a neutrally charged Helium atom since Helium has 2 protons. If the electrons and protons are not balanced, the atom has a charge and is called an ion.

Structure of a Helium Atom

The neutrons however are a different story, they play a role in allowing the nucleus to bond together. Changing the number protons would change the element, changing the number of neutrons however changes the isotope. Any given element can have several different isotopes, but not all isotopes are stable. Any time there isn't a proper balance between neutrons and protons, the nucleus will try to rearrange itself into a more stable configuration. This can result in neutrons becoming protons, protons becoming neutrons, or even in the atom splitting into two (known as nuclear fission).

So if the "indivisible" atom can actually be broken down into protons, neutrons, and electrons, can these particles be further broken down? As far as we can tell, electrons are truly fundamental particles. They cannot be further broken down and are part of a family of fundamental particles known as leptons. As for protons and neutrons, they are made up of even smaller particles called quarks. A proton is made of two Up quarks and one Down quark and a neutron is two Down quarks and one Up quark. Quarks, like electrons, are fundamental particles and cannot be further broken down.

And so we have finally arrived at the answer to our original question. If you were to cut the device you are holding now into progessively smaller and smaller pieces, you would eventually end up with quarks and leptons (in addition to a voided warrenty) which cannot be broken down further. Looks like Democrites and Leucippus have the last laugh on this one.

Democrites always has the last laugh


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Welcome to From Simplicity To Complexity!

There is always a sense of accomplishment in understanding something we previously didn't. Whether it's learning how to drive, cook a new meal, or finally figuring out how to program your TV to record Storage Wars, we all get a certain sense of satisfaction out of learning something new.

Maybe I should be using one of the other 12 remotes that came with my PVR...

We as human beings are not unique in our ability to learn new things, but we do have one major advantage over all the other species when it comes to learning: The ability to store knowledge outside of our brains. Other creatures are limited to only being able to pass on what they or others in their group know. You however can read a book written by someone in England over 400 years ago and learn calculus, or know how to assemble a bookshelf using only a small booklet of instructions and pictures. It is this ability to store and transmit knowledge through the ages that has allowed new generations to quickly get up to speed on what has been previously discovered and build upon that knowledge. Breakthroughs that took hundreds of years to make can be absorbed by students in just a few years, allowing them to make breakthroughs of their own to pass on.

You then, sitting there reading this, currently have access to more knowledge than literally any human being who has ever lived. We live at the cutting edge of understanding, being able to benefit from thousands of years of trial and error and endless hours of painstaking observation undertaken by those before us. All in hope of understanding the world we live in just a little bit better and passing it on so that our children may understand just a little bit more.

There is a long way to go, but so far we have made enormous progress towards answering arguably the most important question ever asked: Where did we come from? Although there are some small gaps, we have at our disposal all the knowledge required to piece together a continuous story starting from the beginning of time and ending with today; something that our ancestors would have greatly envied. It is my sincere hope in writing this blog series to tell as much of this story as I can, so that others may feel the sense of satisfaction that comes with understanding the world we live in and our place within it.

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