Atoms 101: A Guide to The Elements
Despite their fashion sense, the ancient Greeks were brilliant enough to have conceived of atoms as the building blocks of the universe.
SUMMARY: Atoms are the basic units of all matter, regardless of whether it exists as a solid, liquid, gas, or plasma. They're made of three key particles: protons, neutrons, and electrons.
Who Discovered The Atom?
Despite draping themselves in bed sheets for every occasion, the ancient Greek philosophers were the original scientists, asking pivotal questions like, "what's it all about, eh?" Without a whiff of technology at his disposal, Leucippus came to the conclusion that all matter is composed of really tiny bits. He took the term from the Greek word atomos which means indivisible.
This was a great starter hypothesis. The universe is indeed made of tiny bits. However, modern physicists have brought us to a more robust conclusion. Atoms are, in fact, divisible. So the name is a total misnomer. And inside atoms, there are all kinds of even smaller quantum particles which behave, even to the greatest minds today, like some terribly spooky magic.
What Do Atoms Look Like?
Niels Bohr devised a way of conceptualising atoms which is so useful that it's still taught in school today. But bear in mind that it's just a representation of what atoms look like—the real things are very different.
This conceptual model offers three basic components to help us understand how atoms work:
- Protons = positive charge (+1)
- Neutrons = neutral charge (0)
- Electrons = negative charge (-1)
Here's an example using helium (He):
The nucleus of every atom contains protons and neutrons. We can think of this cluster as being orbited by much smaller particles called electrons, which reside in different energy shells.
The number of protons, neutrons and electrons present in an atom tells us what species it is. We call these elements. The periodic table offers critical info relating to each element:
Helium is one of the lightest elements, possessing just two protons and neutrons. By contrast, heavy elements have lots of protons and neutrons—think radioactive elements like uranium (U).
So how many types of elements are there in the universe?
How Many Elements Are There?
Imagine a long staircase, where each step represents an element. On the first step, we have hydrogen (H), with just one proton. On the second step, we greet helium with open arms. It has two protons.
The third step is lithium (Li) with three protons. And the fourth step is beryllium (Be) with four protons. You get the idea.
The heaviest element in nature is uranium which has 92 protons. However, physicists have added an extra 26 steps to the elemental staircase by creating man-made elements.
This gives us a total of 118 elements.
Man-made elements are radioactive. Many are named after famous scientists, such as the awkward-sounding rutherfordium (Rf) and einsteinium (Es).
Here's a handy visual of them all, known as the Periodic Table of Elements.
Now let's take a closer look at those zappy little electrons.
What Are Electrons?
Electrons are tiny subatomic particles that carry a negative charge. They act as the primary carrier of electricity in solids.
Electrons move around in their energy shells—more on this when we get to quantum particles later. They play a crucial role in determining how atoms react chemically to one another.
It's handy to know that the innermost energy shell can hold up to two electrons. The next shell can hold up to eight electrons. And the next, up to eighteen. There's a general formula to this: any given shell (n) can hold up to 2(n2) electrons.
Although they're miniscule by comparison, each electron still holds an equal and opposite charge to one proton. So when an atom possesses the same number of protons and electrons, it becomes electrically neutral—or stable.
Now we understand the components of atoms, we can look at how they interact to form atomic bonds.
How Do Atoms Bond?
Bonds allow atoms to stick together and form molecules. For instance, when you have two atoms of oxygen stuck together, you get a molecule of oxygen, or O2, which is very handy indeed for all animal life on Earth.
Atoms are social creatures and take the opportunity to bond with one another whenever the opportunity arises. This is your basic chemical reaction.
Now we need to expand our chemistry vocab. We're going to look at covalent bonds, ionic bonds, and isotopes.
Covalent Bonds: Sharing is Caring
Covalent bonding is the most common way for atoms to get together. It involves sharing electrons between their outermost shells.
Take oxygen for example. Oxygen has six electrons in its outermost shell, with space for two more. It's like that incomplete feeling you get when only six guests turn up to your dinner table reservation of eight.
The easiest way to resolve this is to invite two more electrons to the table. But where can they come from?
Hydrogen steps up. Hydrogen has only one electron in its outer shell. Just one, lonely diner at its table. It really wants a date. And so a hydrogen atom is always on the lookout for one extra electron.
Now, this is where my dinner table analogy gets weird. Because the solution is to have the waiters push the tables closer together—and then have diners hop continuously between tables so that their hosts feel good about themselves.
So what's happening here?
The electrons zap around the conjoined shells, sometimes making oxygen feel happy with eight outer electrons, and sometimes making hydrogen feel complete with two.
Note how the electrons hang out in pairs. They also maintain the furthest distance away from other pairs as possible, repelled by their charges. This is what gives molecules distinct and predictable shapes.
This friendly alliance means that these two elements are drawn naturally together all the time in nature. And when I say nature, I of course mean the entire universe.
Water is one of the universe's best ideas so far. It's great for life on Earth, and makes up 90% of your body, providing an excellent medium for more chemical reactions to take place in your cells.
Water also makes up plant sap. This is critical for animals because plants are, ultimately, our original food source. Whether you're a herbivore, an omnivore, or a hard-out carnivore, there's a humble plant at the bottom of the food chain.
So that's the first type of bond that facilitates life on Earth. What's next?
Ionic Bonds: Daylight Robbery
Instead of politely sharing electrons, some atoms outright steal electrons altogether. This is fine, though, because their victims are willing participants, with excess electrons to give away. There's no foul play in physics.
To make table salt, for instance, a sodium (Na) atom gives up the one and only electron in its outer orbit to an atom of chlorine (Cl), which is so nearly complete with seven electrons.
This gives us sodium chloride (NaCl):
Sodium is perfectly happy with this arrangement because donating an electron means it can drop its frivolous outer shell entirely. Its next electron shell is full, so sodium can rest happy.
Equally, chlorine is in the opposite position because it needs to gain just one electron to complete its outer shell.
Now, chlorine could form a covalent bond with another element in this situation. But if sodium's lurking around, chlorine takes advantage by forming an ionic bond.
There's a key difference between ionic and covalent bonds. It's no longer the electrons that hold the atoms together—but the residual charges of the atoms overall.
That's because sodium is left one electron short to sufficiently balance out its positively charged protons. The atom is now an ion with a positive charge of +1.
Electrically unbalanced atoms are called ions—hence the term ionic bonds.
Likewise, chlorine has one electron too many to be balanced, making it a chloride ion with a negative charge of -1.
But it's all good. The electrons are happy in their shells, which is the primary concern here. And now the positively charged sodium ion is attracted to the negatively charged chloride ion.
These complementary charges hold the two atoms together in a stable molecule. And because there are more than two types of elements involved, it's called a compound.
Isotopes: Deviant Atoms
So far, we've discovered that changing the number of protons in an atom gives you a different element. And changing the number of electrons in an atom is a result of chemical bonding.
So what happens if you change the number of neutrons?
Your atom becomes an isotope.
In the atmosphere, cosmic rays smack into carbon atoms and provide them with extra neutrons. Carbon can go from having six neutrons to seven or even eight neutrons, creating carbon isotopes.
The standard carbon-12 atom becomes a carbon-13 isotope when you add one more neutron, or a carbon-14 isotope when you add two neutrons. As a result, different isotopes of the same element have different atomic weights.
Carbon-14 is radioactive, whereas other forms of carbon are stable. This is useful for carbon dating, where the age of a fossil can be determined based on the decay of carbon-14 atoms.
So What Do Atoms REALLY Look Like?
Earlier, using the Bohr model, we imagined electrons orbiting the nucleus of an atom in the same way we envision planets orbiting the sun.
In reality, though, not only is this conceptual model over-simplistic, it's also completely wrong. Sorry about that.
A more accurate way to think about it is that electrons pop in and out of existence, somewhere within their designated energy shells.
Electron behaviour can seem pretty random—but this behaviour can be predicted in theory. Quantum physics tells us that the presence of electrons in their three-dimensional energy shells can be determined by a mathematical function.
This enables physicists to deduce the probability of electrons being present at a particular location at any particular moment.
Of course, this is also a conceptual representation based on mathematics. Is it even possible to see an atom?
It is. In 2018, David Nadlinger, a PhD candidate at the University of Oxford took this long-exposure photo of a positively charged strontium ion.
Can't see it? Let's zoom in.
Unbelievably, the photo, titled "Single Atom in an Ion Trap" was taken with a DSLR camera. The strontium ion was illuminated by a blue-violet light, and held motionless by an electric field emanating from the metal electrodes either side.
It's the first time we've been able to see a single atom with the naked eye.
Of course, you can see atoms any time you want. The whole world is make of them. Look around you. What you see, to the best of your optical capacity, is the accumulation of countless atoms, making up every single thing in the known universe.