In everyday life, we often encounter three different phase of matter. There are solid substances (e.,g. stones, iron, etc.), liquids (water, gasoline, etc.) and gas substances (air, etc.). The three-phase of these substances can be distinguished based on their ability to maintain their shape and size.
Solids usually maintain a fixed shape and volume. The liquid does not keep an attached form but adjusts its way to the container that is occupied. For example, if we put water in a glass, the shape changes like a glass. If water is put into the bathtub, the shape changes like a bathtub. The volume of liquid is usually always fixed. A glass of water if it is placed in a bath, the amount of water remains a glass. The shape of the water can change, but the size never varies. Keep in mind that the number of solids and liquids can change if given a considerable force.
What about gas? Gas does not have a fixed shape and volume. The shape and size of gas are always adjusted to the shape and size of the container it occupies. For example, if we put gas into a tire in a car, the way of the gas changes like a tire in a vehicle. Likewise with the volume. When in a casing, gas spreads to fill the entire tire space. In this case the number of gas changes like a tire volume. If we blow a balloon (we put air into a balloon), the shape and volume of the air will change like the shape and volume of the balloon.
So far we have only distinguished the three forms of matter based on their macroscopic properties (macroscopic properties = the shape and size of substances). Of course, this is based on the results of our measurements and observations every day. We will see the difference between the three forms of matter based on their microscopic properties. Each substance consists of atoms or molecules. When we say a rock is stable, we never know what happens with atoms or molecules that are inside the foundation so that the stone becomes solid. Likewise with water or air. What’s wrong with atoms or molecules that form pool so that the phase of water is liquid and the atmosphere is not visible.
Substance forms based on microscopic properties
Before discussing the differences in solids, liquids and gaseous substances based on their microscopic features, let’s review an object. For example, stone. If we look carefully at the sand, we will see that each part of the stone sticks together. Even though it is kicked and thrown, its shape and size never change. Usually, all elements of the rock are always in one unit. Why is that? Let’s think for a moment.
Inside the stone, there are atoms or molecules. Now imagine a rock. Try to imagine the sand is composed of small pieces. For more, the pieces of stone become smaller and smaller. Imagine atoms like a ball that is very small in size. Whereas molecules consist of several balls sticking together.
In rock, there are so many molecules or atoms that are very small in size. Can you imagine the atoms in a stone?
The diameter of one atom is about 10-10 m. If you imagine an atom like a ball, then the diameter of the ball is 10-10 meters. Very small and cannot be seen with the eyes … Only imaginable. Molecules are atoms that stick together, so the size of a molecule is more significant than an atom. But also cannot be seen with the eyes.
If atoms or molecules are not in one unit, of course, every part of the stone does not stick together. Every piece of rock sticks together so that the shape of the rock becomes solid. Why don’t atoms or molecules separate?
Indeed, the atoms or molecules are attracting each other. If atoms or molecules do not pull together, of course, they have flown everywhere. Every atom or molecule will say goodbye to a friend. Thus, the pieces of stone will be scattered everywhere. The parts of rock will also be scattered, and we cannot finally see them. Stone pieces are also composed of atoms or molecules. The size of the atom is tiny, so if they separate, of course, we can’t see them … But the reality is not like that.
The stone looks solid, each part of the stone sticks together. Thus we can conclude that the atoms or molecules that form solid objects must attract each other.
The force of attraction between atoms or molecules is an electromagnetic force. The presence of attraction forces makes atoms or molecules close together. When want to collide, the electrons in the outermost part of the atom or molecule repel each other (electrical repulsion). The distaste makes the atoms and molecules move backward. Even though the atoms or molecules move backward, but because there is an attraction, they approach each other again. The atoms or molecules move back and forth (vibrating) while maintaining a minimum distance.
The difference between solids, liquids, and gases based on the actual microscopic properties lies in the strength and weakness of the attraction between the atoms or molecules of the three substances.
In solids, the attraction forces between atoms or molecules are so loud so that atoms or molecules that form solids are always in a fixed position. Atoms or molecules in solids move back and forth (vibrating), but they still vibrate in the same place.
The strength of the attraction between the atoms or molecules form these solids is the reason why the solid form and volume are always fixed. Even if thrown or banged, the shape of the stone or iron is difficult to change because the force of attraction between atoms or molecules is strong. When you put rocks or metal into a bucket or a bathtub, the volume of rock or metal never changes. So the strong attraction between atoms or molecules that make up these solids makes them stay in one unit and their shape looks solid.
The position of atoms or molecules that form solids is like the image (also known as the crystal lattice). This image is enlarged. Atoms or molecules are tiny.
In liquids, the force of attraction between atoms or molecules is less strong, so they are entirely free to move back and forth, overlapping one another. The atoms or molecules that form the liquid can indeed move freely, but they cannot say goodbye to their friends. The magnitude of the attraction can still hold them from being scattered.
The reason why the liquid form can change, but the volume is always fixed. When we put water in a glass, the force of attraction between the atom or the molecule is not strong enough so that the shape of the water changes like a glass shape. When we put water in a bathtub, the less attractive force between atoms or molecules makes water adjust its shape to the shape of the bath. The volume of liquid is always fixed because the force of attraction between atoms or molecules is still able to hold them together. The atoms or molecules that form the water are not scattered, so the volume is always fixed.
The position of the atom or molecule making up the liquid as in the picture (arrow shows the direction of motion).
In gas substances, the attraction between atoms or molecules is weak. They move free because there is no bond between them. A very weak attraction makes the atoms or molecules that form the gas substance scattered everywhere. The atoms that form the gas substance are freer than the atoms that form solid or liquid substances.
The position of atoms or molecules that form gas is as shown in the figure.
A very weak attraction is the reason why the shape and volume of a gas substance can change and why the eye can not see the air. The size of atoms or molecules is so small so that if they are scattered everywhere, then we cannot see them. The size of sand or sugar is much larger than atoms or molecules so that even if scattered, the grains of sand can still be seen with the eyes although it is somewhat tricky.
Solid or liquid substances can be seen because the atoms or molecules are not scattered. The amount of attraction in solid and gas substances is still able to hold them to stay together. The force of attraction on the gas substance is weak so that it is unable to hold atoms or molecules to stay together. This small attraction is also the reason why gas and liquid substances can flow.