In science, matter can exist in three states: solid, liquid, and gas. These three states have distinct properties that allow humans to identify them.
To support teaching your children about states of matter, look at this collection of helpful teaching resources.
Changing States of Matter
Changing state of matter is turning solid into gas or liquid, and vice versa. Everything we see is made of matter, and this matter can change state with the addition or removal of heat.
In KS2, children will learn about the different states of matter. This topic mainly explains how a material’s state of matter can change.
What are the 6 Changes of Matter?
Matter changes state in various ways:
- Melting – changing from solid to liquid
- Freezing – changing from a liquid to a solid
- Vaporization – changing from liquid to gas
- Condensation – changing from gas to a liquid
- Deposition – changing from gas to a solid
- Sublimation – changing from a solid to gas
These changing states of matter occur due to a temperature change. For example, ice (a solid) will melt when the temperature increases and return to the water (a liquid).
Why are There Different States of Matter?
All matter is made up of tiny particles, regardless of what state the matter is in. Every particle within these materials has a certain amount of kinetic energy that allows the particles to move. In a solid material, these particles are tightly bonded together, with minimal movement, to form a single unit that doesn’t change shape or size. However, heating the solid up gives the particles more energy that they can use to move, weakening the bonds between the particles and gradually allowing the solid to turn into a liquid.
In a liquid, the particles are still loosely bonded, but rather than being a rigid bond that holds all the particles within a fixed pattern like a solid, the bonds are much more flexible, allowing the liquid to change shape depending on what container it sits within. The bonds are still close enough that the liquid will retain the same volume, though – it can’t get any bigger or smaller, only change shape. Heating the liquid further still gives the particles enough energy to break the bonds between them almost entirely, allowing the liquid to become a gas.
In a gas, there are no bonds between the particles, so they can move freely, allowing the gas to change shape and volume depending on the available space. In many cases, their particles are so diffused that they’re invisible to the naked eye.
All these processes can be carried out in reverse, converting a gas into a liquid or a liquid into a solid. Throughout all of these changes, the particles in a substance are the same whether it’s in the solid, liquid, or gas state – the only thing that changes is the arrangement and movement of the particles.
Each of these states of matter can also be referred to as a Phase, with changes of state being referred to as phase changes.
What’s an excellent example of how this works in everyday life?
Water is one of the best materials you can use as an example of how changing states of matter work in everyday life. Below 0°C, water freezes and becomes a solid material, ice. Once the ice is brought back over 0°C, it melts, becomes liquid water, and can be heated up to 100°C. At 100°C, water boils and becomes a gas, water vapor.
Although water is effortless to observe, since it’s not too challenging to bring water both to the “boiling point,” where a liquid becomes a gas, and to the “freezing point,” where the liquid becomes a solid, most other materials also behave similarly. Almost every material has a freezing and boiling point the same way water does, but many of them, like most metals, have such a high freezing (or melting) point that it’s tough to get them hot enough to become a liquid. Metals are an excellent example of this – while industrial forges can get metal to melt, it’s not something that can be done without an incredibly intense heat that’s hard to find in the natural world.
Now that we’ve explored why matter exists in different states and how matter can change between them let’s focus on each state and how we can identify them in the world around us.
What are the Properties of Solid Materials?
The properties of solids include:
- Solids stay in one place and can be held.
- Solids keep their shape. They do not flow like liquids.
- Solids always take up the same amount of space. They do not spread out like gases.
- Solids can be cut or shaped.
- Even though they can be poured, sugar, salt, and flour are all solids. So each salt particle, for example, keeps the same shape and volume.
It is because of the way that the particles in a solid are bonded together. They’re very closely packed into a regular pattern, with rigid bonds that hold the particles into a tightly packed structure.
Since the particles can’t move, solid materials have a fixed shape and cannot flow (although materials like sand seem to flow, the individual sand grains can’t change shape or size like water can). It is also hard to compress something made of solid material: the particles are tightly packed together, so there’s no room for them to move into a different position and allow the solid to change shape. Solids will change state of matter when heat is present as the particles start to move.
Some examples of solids that we might find in the world around us are: ice, wood, sand, and metal
It is because of the way that the particles are bonded in a liquid. The particles in a liquid are closely related, but these bonds are looser and more flexible than in a solid, allowing the particles to slide and form random shapes within the mass of liquid. In contrast, solids have a regular, ordered structure of particles.
It is why liquids, unlike solids, can flow and change shape: although the particles are closely bonded together, they can move around within these bonds, allowing the liquid to shift to fill different shapes. The bonds are strong enough that the liquid can’t expand or shrink, however – while the shape of the liquid can change, and it might seem bigger or smaller depending on the container it’s currently held in, the volume of liquid will always stay the same.
These close bonds are also why liquids are extremely hard to compress: the particles are closely packed in, the same as solids, so if a liquid is in a container with a fixed shape so that it can’t further change shape, there isn’t enough space between the particles for them to be compressed further.
Some examples of liquids that we might find in everyday life are: water, milk, cooking oil, and honey
These properties are all caused by how the particles bond in a gas. Unlike in liquids and solids, the particles in a gas have fragile bonds to the extent that they’re barely bonded. It allows the particles to move freely in all directions, not held together in a homogenous mass like liquids and solids. As a result, gases flow like liquids and can expand or shrink to fill the space they currently occupy since the particles move around so freely that the mass becomes highly fluid.
It is also why gases can be compressed, unlike liquids and solids. Since the particles in gases naturally travel freely, when they aren’t compressed, they’ll expand to fill whatever space is available, with lots of space between the individual particles. It means that when placed under pressure, the particles have plenty of space left between them that can be removed as the space the gas fills is compressed.
Some examples of gases we might find worldwide are water vapor (steam), helium, nitrogen, and oxygen.
Changing States of Matter: Examples
Examples of Gas to Solid
The changing of gas to solid is called deposition. Here are some examples of deposition.
- Water vapor to ice – fog transforms directly into ice without becoming a liquid. It sometimes happens on windows during winter.
- Physical vapor to film – thin layers of ‘film’ placed onto a surface using the vaporized film form.
Examples of Gas to Liquid
The changing state of gas to liquid is called condensation. Here are some examples of condensation.
- Water vapor to dew – steam turns from gas to liquid, like morning dew on the grass.
- Water vapor to liquid water – fog makes glasses foggy after moving into a warm room from the cold.
Examples of Liquid to Gas
The changing of a liquid to gas is called vaporization. Here are some examples of vaporization.
- Water to steam is vaporized after being boiled on a stove or kettle, forming thick vapor.
- Water evaporation – water evaporates from a pool or rain puddle during hot days.
Examples of Liquid to Solid
The changing of a liquid into a solid phase transition is called freezing. Here are some examples of changing the state of matter into a frozen material.
- Water to ice – when water becomes cold enough, it freezes and turns to ice. Almost every known liquid turns to ice when cold enough – except helium.
- Liquid to crystals – lots of liquids freeze during the process of crystallization. Liquid forms into what is called a ‘crystalline solid.’
Examples of Solid to Liquid
The changing of a solid into a liquid is called melting. Here are some examples of melting matter from a solid to a liquid.
- Rocks to lava – stones in volcanos can be heated until they become molten lava.
- Metal to molten liquid – metals can be molten down and reformed into solid.
- Ice to water – ice returns to its water form after being left in temperatures above freezing.
Examples of Solid to Gas
The changing of a solid to a gas is called sublimation. Here are some examples of sublimation.
- Dry ice sublimation – carbon dioxide is called ‘dry ice’ and sublimates at room temperature.
- Freeze-drying – water can be sublimated in food produced by using a vacuum to remove air particles.
Are There Other States of Matter?
There is a fourth state of matter: plasma. Plasma is very similar to gas, but it’s made up of particles that are charged with energy that causes the particles to split and form a different configuration. Unlike the other three states of matter, it’s unclear what causes matter to transition into plasma, although we know it depends on positively charged particles. However, although we don’t fully understand plasma, it can be observed in the world around us.
Two examples where plasma is on show in everyday life are in neon lights and lightning, but in space, plasma’s most common because all the stars, including our sun, contain vast quantities of plasma. As a result, plasma is the most abundant form of ordinary matter in the universe, excluding dark matter and dark energy.
However, if you’re looking for a straightforward explanation for younger children, don’t panic! Most academic curriculums don’t cover plasma until university, so you don’t must worry about covering it with more youthful pupils.
What Determines a Material’s State of Matter?
While the primary determiner of a material’s state of matter is temperature, as we’ve already discussed, another significant factor we haven’t mentioned is pressure. Because humans can’t survive outside of a relatively narrow band of atmospheric pressures (between 0.0621 standard atmospheres and 30 standard atmospheres) without using specialized gear, it can be a little difficult to observe the role pressure can play in determining a material’s state of matter. Still, there are environments and conditions where it can be seen.
Generally speaking, when the pressure exerted on a substance increases, it can cause the substance to condense. Decreasing pressure can cause it to vaporize. For some types of rock, decreasing pressure can also cause them to melt.
It is most easily visible when we look at the water around hydrothermal vents at the bottom of the sea. Although the temperatures around these vents are incredibly high, reaching around 400°C, four times the boiling point of water, the pressure is so high that the water cannot vaporize and stays as a super-heated liquid!