What is matter?

Matter is the ‘stuff’ that makes up everything in the universe. Matter is made up of atoms. An atom consists of protons, neutrons, and electrons. Protons are positive, neutrons are neutral, and electrons are negative. 

Solids, liquids, and gases are types of matter. The particles in each are arranged differently. 

What are solids?

Solids have a definite shape, definite volume, and definite mass. This is because the particles in a solid are packed very closely together in a regular pattern. So the particles in a solid have very low kinetic energy. The strong forces called bonds attract the particles towards each other; therefore, the particles can vibrate, but they can’t move from place to place. The shape of a solid doesn’t change unless it’s broken, cut, or squashed into a different shape.

Examples of solids are a table, a chair, a pan, etc. 🍳

Properties of solids:

• Definite shape
• Definite volume
• Definite mass
• Particles very close together
• Low kinetic energy
• Particles can’t move around 

What are liquids?

Liquids have a definite volume but no definite shape. This is because the particles are close together but they are arranged in a random way. This means that the particles are able to move around each other slightly. The bonds between the particles are strong enough to keep the particles close together; but they are weak enough to allow them to move around each other. Liquids are also very hard to compress, and they can take the shape of the container that it is in, for example, a bottle. The volume of a liquid stays the same. 

Examples of liquids are water and petrol. 💧

Properties of liquids:

• Definite volume
• No definite shape
• Particles close together
• Particles can move around 

What are gases? 

Gases have no definite shape or volume. The particles in a gas have a lot of space between them and are arranged in a random way. The strength of the bonds between the atoms are weak; therefore, the particles are free to move in any direction, and they have high kinetic energy. A gas changes shape according to the container that it is in. The particles in a gas spread out to fill large containers when the gas is compressed. The space between the particles is reduced to fit small containers. 

Examples of gases are oxygen and carbon dioxide. 💨

Properties of gases:

• No definite shape
• No definite volume
• Particles are far apart
• High kinetic energy 
• Particles move in any direction

There are three states in which matter can exist: solids, liquids, and gases. 

Matter can change in different ways. 

There are six ways in which matter can change:

• Melting 
• Freezing
• Evaporation
• Condensation
• Deposition 
• Sublimation 

When a solid turns into a liquid, it is called melting. For example, ice turns into water when it is left at room temperature. 

When a liquid changes into a solid, it is called freezing. For example, water changes into ice when it is cold enough to freeze. 

When a liquid changes into a gas, it is called evaporation. For example, water changes into steam when it is boiled in a kettle.

When a gas changes into a liquid, it is called condensation. For example, water vapour changes into liquid water when moving into a warm place from a cold place. For example, when you have foggy windows. 

When a gas changes into a solid, it is called deposition. For example, when water vapour changes into ice. This can happen directly when it is very cold and can usually happen on windows during the winter.

When a solid changes into a gas, it is called sublimation. For example, snow or ice can change directly into water vapour without melting first into water. This can happen directly when it is very cold and usually happens on windows during the winter. 

Reversible changes

Reversible changes refer to any changes made that can be reversed.

Changing states of matter 

Changing states of matter are always reversible. For example, chocolate melts when it is warm, and it sets hard when it is cold. Boiling water evaporates as steam and then it condenses back as water. These are both examples of reversible changes. So even when the state of matter is changed, it can still be changed back to its original.

Mixing materials 

When different materials are mixed together, they can usually be separated again using separating processes.

There are four processes for separating mixtures:

• Filtering 
• Sieving 
• Evaporation
• Condensation  

Solid + liquid

When a solid is mixed with a liquid, the process can be reversed by filtering. This process consists of moving a mixture through a filter. This can usually be a paper filter containing small holes. When the mixture is poured through the filter, the liquid passes through the filter, and the solid does not pass the filter; therefore, we can separate the solid and the liquid. 

Solid + solid 

When solids are mixed together, the process can be reversed by sieving. A sieve is a tool with a net attached that has holes. Sieves can come in different sized. When a mixture is placed in the sieve, the smaller solids pass through the sieve, helping to separate out larger solids from smaller solids.

Soluble solid + liquid 

When a soluble solid is mixed with a liquid it will dissolve in the liquid to form a solution. For example, when salt is dissolved in water, it forms a salt solution. The process of dissolving can be reversed by evaporation and condensation. Evaporation consists of heating the salt solution, this leaves behind the solid salt, and the water turns into water vapour. Condensation consists of cooling the water as it evaporates. 

Irreversible changes 

Irreversible changes refer to any changes that can’t be undone as a new material is formed. 

Some examples of irreversible changes are:

• Burning 
• Rusting metal
• Heating food
• Mixing ingredients 

Burning 

Burning is an irreversible change. When wood is burned, it becomes ashes and cannot be changed back into wood. 

Rusting metal 

Rusting metal is an irreversible change. When a metal is exposed to oxygen and water for long enough, a reaction called oxidisation occurs. This causes the metal to rust. 

Heating food

Heating food is an irreversible change. An example of this is cooking an egg in a pan. The cooked egg can’t be reversed back to a raw egg.

Mixing ingredients

Mixing ingredients is an irreversible change. An example of this is when making bread you have to mix all the ingredients to make dough. Once the ingredients are all mixed together, they can’t be separated as now the ingredients have permanently changed.