So what is matter? We are surrounded by matter. We are made of it and we interact with it everyday, all day, even after we pass away. When we think of matter, we typically think of solid objects. A table, a book, a mobile phone are examples of solid objects. But water, oil, clouds or even the air we breathe are all forms of matter. We can classify all forms of matter in three states: solid, liquid and gas. The most common example of illustrating the three different states of matter is that of water. When solid, we call it ice, when liquid, it’s plane water and when gas, it’s steam. But what makes all these three different forms of water essentially the same? What is it about ice that is identical to steam and water even though it looks and feels different from its other forms?
It comes down to how close we look at the different forms of water. From our normal, day-to-day interaction with that substance, we cannot see exactly what it is composed of. Yes, a glass of water is made up of hundreds of drops of water. And when steam condenses on a surface, it forms tiny droplets of water. But even smaller than that, if you look even closer, within each tiny droplet there are billions of smaller units of water. We call these molecules. At this level, it is indistinguishable whether the molecule we’re looking at is one from ice or one from steam. That is to say, the three forms of water are all made up of the same tiny molecules.
How big is a molecule of water? And why can we not see these molecules in a drop of water or in an ice cube? The first question should perhaps be rephrased as “How small is a molecule of water?”
A molecule of water is so small that you need more than thirty million billion billion of them to fill in a one litre bottle. That’s three followed by twenty five zeros. A clearly astonishing number of molecules indeed! If we need that many molecules then they must be really, really small to be able to fit in a bottle. And being that small, a molecule of water is invisible to the naked eye. We can however have an idea of what they look like using powerful instruments and we can use a little bit of chemistry as well to figure out what a molecule of water is like. At a closer look, a molecule of water resembles Mickey Mouse’s face: a big central circle and two smaller ones at the top for the ears. The three small circles represent what we call atoms. These are even smaller than molecules. Atoms when put together form molecules. A molecule of water is composed of three atoms. Two atoms of hydrogen (for the ears) and an atom of oxygen (for the face). And whether you are looking at ice, steam or water, at this very, very small scale, their molecules will look the same. They won’t behave in the same way, because steam molecules tend to be more restless and frantic than water or ice molecules. Ice molecules are very organised, relatively speaking. Water molecules are somewhat in between those two states. Some degree of freedom to move about but not so rigid like their ice counterparts and not so crazy like their steam buddies.
In fact, that type of behaviour is typical of all forms of matter. Imagine a very large hall, mostly empty except for a group of people huddled close together. Let’s say that we have twenty rows of people and in each row there are twenty people. So we have this block that is four hundred people big. Everyone is standing in a block formation and almost military in their stance. From time to time, they can turn and talk to each other, softly, move their arms about slightly but that is it. They cannot walk about or swap places with one another. Their position relatively to each other and their behaviour (close and quiet) represent a solid. This is the picture we generally have of a group of atoms or molecules of a solid substance.
Now the hall is such that its floor can be heated. So we start heating the floor. Not so hot that it’s uncomfortable but hot enough to make everyone feel the heat. Everyone wants to move away to somewhere cooler but they don’t know that it’s equally hot all over the floor in the hall. So they move around. As one block. That’s important. We still want to keep everyone as one block but now the block can move as a whole. And they want to spread out yet keep holding on to each other. They no longer have this regular formation of a block but yet everyone is still linked to the other. They start talking a bit more loudly now as if to express how agitated they’ve become. They are now behaving like the molecules in a liquid. Next we increase the heat so that it becomes slightly uncomfortable. Now the group of people becomes more restless and they let go of each and run about in a very excited state, some jumping, others dashing from one end of the hall to the other. It’s now complete mayhem. Everyone is on their own, shouting, running, jumping, bumping into each other, trying to occupy the whole hall and being generally ecstatic. This resembles the behaviour of gas molecules. They are no longer restricted and static like the solid molecules and no longer linked to each other like the liquid molecules.
What we’ve described here is how matter changes state from being liquid to solid to gas. And this was done by adding energy or heat to the molecules, represented by the floor being heated. Place an ice cube on a hotplate and you can see how it melts into a liquid and as the liquid gets warmer, it gradually turns into steam. Why does this have to happen? Why should this change of state take place at all? Why can’t the ice cube simply get warmer and retain its shape and size? We’ll answer these questions in a different blog. In this one, we’re more interested in finding out about matter rather than how it changes.
So, we moved from molecules to atoms. We’ve understood that substances which have the same molecules or atoms must be the same substance, regardless of the state they are in. But what about atoms? Is there anything smaller than an atom?
In a previous blog, I’ve explained the structure of an atom. Both theory and experimentation have shown us that the atom is composed of a central core called the nucleus and a cloud of orbiting electrons. Particles which make up the nucleus are called protons and neutrons. A water molecule is composed of one oxygen atom and two hydrogen atoms. A hydrogen atom itself is composed of one proton and an electron. It doesn’t have any neutron. An oxygen atom is composed of eight protons and eight neutrons in its nucleus and has eight orbiting electrons. Protons are subatomic particles themselves composed of even smaller particles. Of course, we didn’t find this out straight away. Until over a century ago, before the discovery of the subatomic particles, we thought that the atom was the fundamental unit of matter. That is, there can be nothing smaller or more basic than an atom. But of course, reality turns out to be different.
We’ve found out over the years that what we thought were elementary particles were themselves composed of more basic particles. And so the proton, it turns out, is made up of three particles called quarks. Similarly, neutrons are made up of quarks, albeit of different characteristics. Electrons, however, is so far indivisible. It is, until now, a truly fundamental particle.
So all those particles put together are what give rise to matter. From your kitchen table where ice is melting into water to the particle colliders at CERN, there is a connection. The ice turning into water retain certain property that makes both of them (the ice and the water) to be essentially the same substance. This property lies in the molecules that make up this substance. And what about the molecules themselves? Well, they are also made up of even smaller parts. And as we keep on probing further into matter at CERN, we realise that not only is all matter (chairs, paint, methane, ants, daffodils, the sun, the flu virus, foam, the wind, the stars and absolutely every thing) composed of the same units (quarks and electrons) but we might eventually find this most elusive particle called the Higgs boson. What this particle is and why is it so sought after, I’ll explain in the next blog.