1.1 States of Matter 

Matter is basically anything that has a mass and takes up space. The book you are reading, your body, the air you breathe and basically everything around you (Living and non-living things) are matter.

*So, is energy matter? No. Energy is a property of matter but not matter itself because energy doesn’t really take up space does it.

Can you try to categorize them into three groups? Look around and what do you see? The book or pen you are holding is hard, you can touch it and it has a fixed shape right. So that is a solid. What about water? You can touch it and all, but is it a solid? No, because even though its tangible you can pass through water easily since it has no definite shape (it takes the shape of its container). Therefore, we will call it a liquid. Then what about the air you breathe? You can pass through it and it has no shape but it’s not a liquid. Why? Because a gas, unlike a liquid, doesn’t have a fixed volume. I will explain this later in the gas section.
Therefore, the three states of matter are solid, liquid and gas. Now that we have a basic understanding let’s learn the technical stuff.


A solid has a fixed shape where the particles are closely packed together in a pattern. In other words, the particles are arranged in a lattice.

Densely Packed
Fixed Shape
Fixed Volume
Only vibrations
Strong Forces of attraction


The particles in this lattice cannot move around. They can only vibrate. Therefore, you can’t put your hand through a solid unless you break it. Why do you think the particles cannot move? It’s because they have very strong forces of attraction between them.

Is it possible to break or weaken these forces so that the particles can move around and flow? Yes, it is, but then it would stop being a solid. How would you go about doing that? (Hint: Ice turning into liquid.) It’s heat. If you heat a solid long enough it could break down and melt into a liquid. When you heat a solid, the particles start vibrating faster and faster until the forces weaken. In other words, the particles gain more kinetic energy (energy to move). If you heat it with enough energy it will gain enough kinetic energy to lose its shape and turn into a liquid. The best example of this is ice turning into water.

Ice melts to liquid at room temperature. But what about a piece of copper? You would have to heat it at 1085 C for it to melt. Why do you need so much energy to melt metal but so little to melt ice? This is because the bonds between the particles in ice is much weaker than the bonds in a solid piece of metal.
Examples of melting: Ice melting to water, candle melting, Butter melting


The particles in a liquid can move around to a certain degree of freedom. As a result, they have a lower density than solids. The particles can touch (particles sont really touch in the literal sense; further explained in 'Types of Bonding'.) but their attractive forces are weaker. Therefore, they can slide over each other and move around. However, the attractive forces are strong enough for the liquid to have a fixed volume. What does that mean? It means that if you have a liter of liquid it will still be a liter even if you change the volume of container or spill the liquid on the ground. It cannot be compressed.

Loosely Packed
No Fixed Shape
Fixed Volume
Particles slide over each other
Strong Forces of attraction

Now we know that we can melt a solid to a liquid. But can this be reversed? Yes, it can because changing state is a physical change; there is no change in the chemical composition of the matter.  But you must take away the amount of energy that you gave one state to turn into another state. For example, if you gave (Heat) an A amount of energy to a cube of ice to turn to liquid; you would have to take away (Cool) an A amount of energy to change it back to ice (solid). This process is called freezing.

As discussed earlier, if you heat a liquid it will boil and turn into a vapor or gas. When you start heating a liquid the particles get more kinetic energy and they start bouncing further and further away from each other. If you give it enough energy the particles will break away to form a gas. 

What about the puddles of water that eventually dry out? We don’t heat them but they eventually turn into a vapor and the liquid disappears. The process that is happening in this case is called evaporation. Evaporation occurs because the particles on the surface of the liquid are moving faster (higher kinetic energy) than the particles deeper in the puddles. It is much easier for them to break away from the rest of the particles. As a result, all the liquid slowly breaks away to form vapor. This process is much faster if its out in the sun because the sun heats the surface of the liquid which provides more energy to the particles.
Examples: Boiling water, water puddle drying out in the sun 

As discussed earlier a liquid can be changed back to a solid. Similarly, you can change a gas back to a liquid because changing state is only a physical change in the matter. This process is called condensation. If you cool the gas and pressurize it by bringing the particles close together it will become a liquid.
Since the particles in liquids can move around what will happen if put different types of particles into a liquid. The particles will collide with each other and mix. Therefore, if put sugar in water, it will dissolve to give you a sugary solution. The sugar particles will spread and mix with the water particles. This process where particles can mix together and spread out is known as diffusion.
Experiment: Potassium Permanganate in water


The structure of a gas is the least dense since the particles have the most freedom. In other words, the forces of attraction between the particles is very weak. Therefore, they have no fixed shape and volume.

Very Loosely Packed
No Fixed Shape
No Fixed Volume
Particles move about freely
Weak Forces of attraction

If you put a sample of gas in a 1-liter container the gas’s volume is 1 liter. But if you take that same amount of gas and put it into a 2-liter container then what’s the volume of the gas? The gas will spread around the new container and the volume of the gas changes to 2 Liters. Isn’t that very interesting.

Now what happens if you heat a gas? Will it change state or is gas the final state? There is another state of matter called plasma. This is achieved when you heat a gas to a certain degree. Plasma is a subset of gas, but its properties are completely different which is why it is considered the fourth state of matter. But we will not discuss it because it is an advanced topic. For now, just know that there are three main states of matter: solid, liquid and gas. 

As discussed earlier, you can change a gas back to a liquid because changing state is only a physical change in the matter. This process is called condensation.

Like liquids, gases also diffuse. However, gases diffuse much faster than liquids because their forces of attraction are much weaker. Example: If you spray lavender air freshener in one side of the room, eventually the whole room will smell of lavender. The particles have evenly distributed themselves around the room since they hate being crowed unlike solids. Using a lighter gas and increasing temperature will increase the rate of diffusion.
Experiment: NH3+HCl→  NH4Cl

Finally, lets talk about compressibility of gases. Only gases can be compressed because unlike solids and liquids they have so much free space in between their particles. What do you think happens to pressure inside container when you compress a gas? It increases because you are jamming more gas particles into a small area and they do not like that. They want to break free so they push against the walls of the container with a lot of force (more pressure). Can you think of any situation where this is useful? Examples: Bicycle tires support your entire weight on a cushion of air, pressure cookers cook things much faster than normal cookers, you can easily transport a lot of gas by compressing it into a small container (propane gas tanks and oxygen cylinders)

Heating Curve

Now that we understand how solids, liquids and gases can transition between states we should look at a heating curve and understand how to read it.

Heating curve is a graph that shows the phase transitions of a substance as heat is added to it. Lets look at the heating curve for water.

Solubility Curve

As stated earlier, when certain solids are mixed with certain liquid they dissolve. These solids are said to be soluble. However some solid cannot be dissolved. These are called insoluble solids.

When a solid dissolves in a liquid the final product is known as a solution. The liquid is called a solvent and the solid is called a solute.

As the solute breaks apart in the solvent, the particles spread around and mix with the solvent particles. The solute particles form new bonds with the solvent particles. These new bonds are stronger that the bonds of the particles before the solid was dissolved. As a result the particles stay mixed to form a solution.

You may wonder if there is a limit to the amount of solid that can be dissolved in a fixed amount of solvent? There is a limit but it is dependent on temperature. A saturated solution has the maximum amount of solute that can be dissolved at a particular temperature. But if you increase the temperature you can dissolve more. This is why dissolving sugar in hot water is much easier that in cold water.

By now you may have realized that solubility changes with temperature. This means that we can plot a graph with respect to temperature to better understand solubility of substances and compare them. These graphs are known as solubility curves. Look at the example below for sugar and salt.



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