Subatomic particles
We have already discussed that matters are made of particles, and atoms are the smallest unit that we can separate into during a chemical process. But that doesn't mean atoms are the smallest particles.
In fact, if we zoom into atoms, we'll realize atoms are not like a meatball or golf ball, they're actually made of many other particles that are smaller than the atoms themselves. We call these particles as subatomic particles.
Although in chemical processes we do NOT break down an atom, it is important for us to know what's making up an atom so that we could understand the behavious of atoms during a chemical process. It is also crucial for us to understand how atoms could give rise to molecules. Therefore, in this post, we'll take a look at these lovely little subatomic particles.
Nucleus
Below shows a much simplified illustration of what you may see inside an atom. Let's focus on the black circle first, which represent the nucleus (Plural nuclei), which sits at the center of an atom, and carries most of the mass of the atom.
As we mentioned just now, the above illustration is very much simplified, actually oversimplified. The nucleus shown here, is way much larger than it actually is. A nucleus inside an atom is like a pea in the center of a football field, or \( \ce{\frac{1}{100,000}} \). It is virtually impossible for us to draw both the nucleus and the whole atom clearly in the picture. Nevertheless, the key takeaway is that nucleus sits at the center of an atom, and is very small as compared to the atom.
Protons
The first thing we're going to talk about is proton, which is a subatomic particle inside the nucleus, possessing a relative mass of 1 unit, and carrying a positive charge of 1 unit (or simply \( +1 \)). We use the symbol \( \mathbf{p^+} \) for protons.
Take note we're saying protons have a relative mass of 1 unit, instead of 1 gram. In fact, a proton has a mass of \( \pu{1.6726219E-27} \mathrm{kilograms} \). But it is very troublesome to write this number every time when we want to discuss about the mass of protons. Therefore, we define \( \pu{1.6726219E-27} \mathrm{kilograms} \) to be 1 atomic mass unit (amu), same as what you do when you say 1 pair of shoes is equivalent to 2 shoes. Therefore, when we say 2 amu, it will be:
\[ 2 \times \pu{1.6726219E-27} = \pu{3.3452438E-27} \mathrm{kilograms} \]
The same principle applies to the charge of protons. A single proton does not really have a charge of 1C (coulomb, unit of charge), but rather \( \pu{6.241E18} \) protons together give 1C of charge. That means a proton alone only carries \( \pu{1.6E-19 \mathrm{C}} \) of charge. Once again, we define the charge that a single proton has to be 1 unit. That allows us to simplify the workload when we need to calculate the charge of any particle.
Neutrons
Neutron is the other subatomic particle that could be found in a nucleus, which has almost the same mass as a proton (1 amu) but has zero charge. We use the symbol \( \mathbf{n} \) for neutrons.
Just a reminder, nucleus itself is NOT a subatomic particle. Instead, nucleus is a small region in the atom where protons and neutrons reside.
Shell
Now let's walk away from the nucleus for a moment. Remember we have said that the nucleus is very small as compared to the atom? The next question would be what about the rest of the atom? Well, the answer is: there are electrons.
Electrons
Electron is the third type of subatomic particles that is important to us as chemists. Electrons stay outside of the nucleus, and are continuously moving around the nucleus.
In early days, people believed that electrons are travelling around the nucleus just like the Earth does around the Sun. Electrons were thought to travel in defined orbits with certain speeds. Meanwhile, depending on how far away they are from the nucleus, electrons were said to be residing in orbits of "level 1", "level 2", and "level 3", etc. "Level 1" orbit is the nearest to the nucleus, just like the orbit of Mercury. "Level 3" orbit would then be similar to the orbit of the Earth if you compare an atom to the solar system. However, this has been proven wrong, or rather oversimplified we shall say. We're going to talk about how electrons are really moving in atoms in the next couple of posts.
Let's focus on electrons themselves for now. Electrons are charged subatomic particles. They have the same amount of charge as that of protons but they are negatively charged, in one word, charge of \( -1 \).
On the other hand, electrons have negligible mass as compared to protons and neutrons. In fact, electrons have mass of \( \frac{1}{1823} \mathrm{amu} \), but scientists haven't even found any atom with more than 182 electrons. The mass of an atom primarily comes from its protons and neutrons, but electrons do contribute to the overall charge of a particle.
To wrap up, an atom is made of protons and neutrons which stay in a small region in the center of the atom (the nucleus), together with electrons which are always moving outside of the nucleus. Protons and neutrons have mass of 1 amu while electrons have negligible mass. On the other hand, electrons have charge of \( -1 \) and protons have charge of \( +1 \), while neutrons have no charge.
| Subatomic particles | Charge | Mass | Location |
|---|---|---|---|
| Protons | \( +1 \) | 1 amu | Nucleus |
| Neutrons | 0 | 1 amu | Nucleus |
| Electrons | \( -1 \) | \( \frac{1}{1823} \mathrm{amu} \) or Negligible | Shells |
Subatomic particles summary
Next
Now that we have learnt about various subatomic particles, next we'll discuss about the significance of these particles and they're related to our work as chemists.