# Particle Model of Matter

Have you ever wondered what rules govern the different states of matter? The particle model of matter is one of the most important theories of modern physics, and also explains why it's harder to make a pot of tea at the top of Mount Everest than at the base! We're going to take a broad look at the particle model of matter so that you can also improve your understanding of how different states of matter work. A state of matter is one of the distinct ways that matter can exist. We are going to look at three states of matter: solids, liquids and gases.

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Contents

## Particle Model of Matter Definition

Before we can go any further, we need to define the particle model of matter. Once we have done that we can talk about the specifics of how it works and what it means. So what is the particle model of matter?

The particle model of matter is a theory that explains how the particles that make up a substance are arranged, and how they move and interact with each other.

There are rules within the particle model for each of the main three states of matter that you may already be aware of. These main states of matter are solids, liquids and gases. Each of these states of matter consist of a different arrangement of particles, with different amounts of energy and different ways that these particles interact with each other. The table below outlines the differences between each state of matter.

 State Solid Liquid Gas 2D Diagram Description of Particle arrangement Regular arrangement Randomly arranged Randomly arranged Relative Energy of Particles Low energy Higher energy Highest energy Movement of Particles Vibrating in a fixed position Moving around each other Moving with speed in any direction Distance Between Particles Very close Close Far apart

We should also discuss how a material can change between each of these substances depending on its temperature. This is because the heat energy of an object is just the kinetic energy for each of the particles. In other words, the hotter something is the more its particles like to move around. The particle model of matter is able to explain the entire phenomena of the experience of heat. These changes of state are physical, however, the amount of a substance both before and after the state change remains the same. No new matter is created and no matter is destroyed, the only thing that has changed is the arrangement of particles.

## Examples of the Particle Model of Matter

There are examples of the particle model of matter all around us. As we have discussed state changes, let us take a look at an example of a material changing state to help you wrap your head around it.

A useful example for explaining the particle model of matter is water; we use it in our day-to-day lives and have likely seen each of its states and how it changes between each of these states. We know that the solid form of water is ice and that the gaseous state is steam.

For water to become solid, it needs to be kept below 0oC (at atmospheric pressure), which slows down the vibration of each of the molecules of the water until bonds are able to be formed between the water molecules. If we return the ice to an environment with a temperature above 0oC, the particles will slowly gain energy until the ice has melted and become water again.

For water to become a gas, it must be boiled, which gives energy to the water molecules. This requires that the water be heated to above 100oC, and slowly the water you have will boil away. This is because the water molecules were given enough energy to break each of the bonds holding them together, and enter the gaseous state known as water vapour.

## The Main Points of the Particle Model of Matter

There are 5 main points that you should remember about the particle model of matter, as they are the basis for the entire theory. These will also help you when answering exam questions on this topic.

1. All matter is made up of particles. It doesn't matter if these are atoms, molecules or ions, everything is made up of a form of particle.

2. Every particle has a motion, it may be slight but even the coldest object in the universe contains particles vibrating by a small amount. Particles just can't keep still!

3. All of the particles within a single substance are identical.

4. Temperature is the main thing that affects the speed of a particle moving. If you increase the temperature of an object, the particles in that object are just going to move faster. Likewise, if you decrease the temperature, those particles will slow down, but they will never completely stop moving.

5. In gases, there are often massive spaces between particles, as they move around at such high speeds that they are able to overcome the forces of attraction between particles. This is different to solids and liquids, as they do not have enough energy to break the bonds that hold the particles together.

## The Particle Model and Pressure

We know what the particle model of matter is, but you also need to specifically be able to talk in more detail about how gas is treated within the model. A by-product of talking about gases within the particle model is the idea of pressure, which we will also take a quick look at.

### Particle Motion in Gases

The particles within gases are constantly moving, and this means they can end up exerting an amount of pressure on the walls of their container. Pressure is exerted by gas when the particles collide with something, either each other or the boundaries of the container the gas is being held in. Therefore, the volume of a container can play a role in the amount of pressure being exerted by a gas, as a small volume will lead to more collisions than a larger volume for a gas with the same amount of particles. In other words, if you changed the temperature of a gas that was being held at a constant volume, the pressure exerted is the value that would change.

The temperature of a gas is related to the average kinetic energy of the molecules within it.

### Pressure in Gases

Unlike solids, which can only be compressed a small amount, gases can be compressed massively, taking up far less space than they might otherwise need. The outwards push that is exerted by a gas in a container is called pressure, which is an outwards force that is exerted upon the walls of a container that is holding a gas.

For a fixed mass of gas that is being held at a constant temperature, the relationship between the pressure and the volume can be expressed using the equation below:

$pV=k$

or in words

$\text{pressure × volume = constant}$

Each of the values and their units are outlined below:

• p is pressure, which is measured in pascals (Pa)
• V is volume, which is measured in metres cubed (m3)
• k is some constant value

## The Experiment for the Particle Model of Matter

Whilst we often use experiments to prove a theory or provide evidence that supports one, the experiment surrounding the particle model of matter does not serve the same purpose. This experiment is actually just something we can see that can be explained by the particle model of matter. It doesn't provide any sort of proof for or against the particle model of matter itself.

This practice explores the density of materials. Calculating the density of these materials requires an equation, which is the value of the mass divided by the volume.

$\rho =\frac{m}{V}$

$\text{Density =}\frac{\text{Mass}}{\text{Volume}}$

Where$\rho$is the density in kilograms per meter cubed$\left(\mathrm{kg}/{\mathrm{m}}^{3}\right)$,$m$is the mass in kilograms$\left(\mathrm{kg}\right)$, and$V$is the volume in metres cubed$\left({\mathrm{m}}^{3}\right)$.

Remember, when you are performing this experiment, you need to record all of your masses accurately. Make sure you measure and observe each object's mass and volume and make sure you use the correct apparatus for measuring the object, depending on how irregularly it is shaped. There are three different ways for you to measure density, depending on the three different types of objects, which we will go through now.

### Regular Solids

1. Measure the dimensions of the solid. If the shape is a cuboid then the measurements you should be calculating are the length, width and height. You should measure each of these lengths a few times each, and if they vary you must calculate the mean of each length. Once you have these values you can calculate the volume.

2. Once you have completed that, measure the mass of your object.

3. You should now have the right values to calculate the density.

4. If you know what material your object is made of, you can look up its true density, and compare both of these values.

### Irregular Solids

1. The first thing you should do is make sure your selected object will fit into a measuring cylinder.

2. Measure and record the mass of the object using a set of weighing scales.

3. Add enough water to the measuring cylinder so that the object can be covered up. Measure the volume of the water before placing the object into the cylinder.

4. Place the object into the measuring cylinder, and measure the new volume of the water in the cylinder.

5. You should now be able to calculate the volume of the object by subtracting the second volume of the water from the first volume of the water.

6. Now that you have these values, you can calculate the density of the irregular solid.

### Liquids

1. Make sure you use the correct measuring apparatus to measure everything to a reasonable degree of accuracy.

2. Measure the mass of an empty measuring cylinder. You will need to subtract this from a total mass later.

3. Remove the measuring cylinder from the scales and pour 20 millilitres of the liquid you want to calculate the density of into the cylinder.

4. Measure the new mass of the measuring cylinder including the liquid inside it.

5. Add another 20 millilitres and measure again. Repeat by adding another 20 millilitres. You will now have three measurements to calculate the density of the liquid with.

6. Use every set of results to calculate a value for the density of your chosen liquid. Remember, the value for density can be calculated using the mass and the volume that you calculated after each time adding more liquid.

Remember, a volume of 1 millilitre has the same value as 1 centimetre cubed (1 cm3)

## Changes of State

Another important factor of the particle model of matter is the fact that substances can change from state to state. When a substance changes from one state to another, there is a change in the amount of energy being stored by the substance. This is the only value that changes! A change of state is a purely physical change, which means that the total mass of the substance remains the same. It also means that the change of state is reversible, meaning a substance can go from a liquid to a solid, and then back to a liquid again.

Take a look at the diagram below, which will show you the different state changes that can take place.

Diagram showcasing different state changes between solids, liquids, and gases. For state changes moving to the right, energy needs to be added, but for state changes moving to the left, energy must be removed, StudySmarter Originals

As you can see in the diagram, five different state changes can occur between solids, liquids, and gases.

• Melting - When a solid turns into a liquid
• Boiling - When a liquid becomes a gas
• Condensing - When a gas turns into a liquid
• Freezing - When a liquid turns into a solid
• Subliming - When a solid turns directly into a gas, without becoming a liquid.

## Internal Energy and Energy Transfers

When we talk about a system containing energy, we are generally talking about the amount of kinetic energy and potential energy that is being stored by particles. An energy transfer refers to any time the system changes. For example, water boiling is an example of an energy transfer. We're going to take a quick look at internal energy and energy transfers, but make sure to read the article dedicated to internal energy, which goes into a lot more detail.

### Internal Energy

The internal energy of any system is the amount of energy that is stored within it. In the case of substances, this energy is the sum total of all the kinetic and potential energies of every particle within the substance. In other words, we can say that the internal energy of a substance is the total energy that makes up the system.

Internal energy is the total energy in a system arising from the relative movement, position and interactions of its parts. We say that internal energy is made up of the sum of the kinetic energies and potential energies of the constituent particles of the system.

### Energy Transfers

When a substance is heated, the total amount of energy it contains increases, which in turn increases the amount of energy stored by the particles that make up the system. This will raise the temperature of the substance to a point, after which a change of state will occur. There are two subtopics within internal energy that we need to discuss, the concept of specific heat capacity and the idea of specific latent heat.

#### Specific Heat Capacity

Specifically, the specific heat capacity of a substance is the amount of heat required to increase 1 kilogram of a substance by 1-degree Celsius. Calculating the specific heat capacity of a substance requires us to use an equation! Check below to see what it looks like.

$∆E=mc∆\theta$

$\text{Change in thermal energy = mass × specific heat capacity × temperature change}$

Each part of the equation is expanded upon below:

• $∆E$is the change in thermal energy, measured in Joules$\left(\mathrm{J}\right)$
• $m$is the mass, which is measured in kilograms$\left(\mathrm{kg}\right)$
• $c$is the specific heat capacity of the given substance, which is measured in joules per kilogram per degree Celsius$\left(J/kg°C\right)$
• $∆\theta$is the change in temperature, measured in degrees Celsius$\left(°C\right)$

#### Change of State and Specific Latent Heat

When a substance changes state, it is extremely likely that it is either being heated or cooled. Therefore, we know that a change of state is accompanied by a change in energy. The energy required for a substance to change its state is called latent heat. When a substance is changing state the temperature of the substance doesn't change, however the amount of internal energy being stored changes.

Whilst the temperature may remain the same during a change of state, we know that all of that energy needs to go somewhere! When a substance is melting or evaporating, the internal energy increase allows bonds between particles to break, whereas during condensing or freezing, the energy goes towards forming new bonds between the particles.

There is an equation for specific latent heat that you will be given on your equation sheet, but let's go over it here as well.

$E=mL$

$\text{Energy for a change of state = Mass × Specific latent heat}$

Where each value means the following:

• E is the energy required for a state change to occur, or simply the energy, which is measured in joules (J)
• m is the mass of the substance and is measured in kilograms (kg)
• L is the specific latent heat of the substance, Specific latent heat is measured in joules per kilogram (J/kg)

The topic of specific latent heat has a lot more to cover than we can look at in this quick overview, so head over to the article dedicated to specific latent heat.

## The Importance of the Particle Model of Matter

We need to understand the particle model of matter because it is a basis for how we understand the physical world surrounding us. Firstly, it provides a reasonable explanation for how matter behaves and secondly it explains that particles of matter are always moving, whether they are a solid, liquid or gas. What defines each of these states is the speed and size of the vibrations that occur in each state.

We think that matter itself is motionless because we do not see the particles in a solid vibrating against each other, and we cannot see the particles of a gas flying in front of us, or into and out of our lungs as we breathe. It can also be used to explain what happens in a change of state.

## Particle Model of Matter - Key Takeaways

• There are three main states of matter: solids, liquids and gases. Each of these states has a distinct amount of energy within each of the particles, and the distance between the particles gets smaller as you go from gas to solid.
• The most easily observed example for the particle model of matter is water, as we have observed it in ice cubes and when boiling water for making tea and coffee.
• We know there are 5 main points within the particle model of matter, make sure you have them memorised.
• Particles can be either atoms, molecules or ions, but any material is made up of a single type of particle.
• The rule for calculating density is to take the mass and divide it by the volume, and the unit for density is kilograms per metre cubed. The equation is $\text{density =}\frac{\text{mass}}{\text{volume}}$
• Changes of state are where a substance changes from one state to another, i.e. From a solid to a liquid, or a liquid to a gas.
• Internal energy is the sum of all of the energy within the substance. The internal energy of a substance is important for understanding how a substance changes its state, as well as energy transfers.
• The specific heat capacity is the amount of energy required to heat 1 kilogram of a given substance by 1-degree Celsius. The equation for calculating specific heat capacity is: $\text{Change in thermal energy = mass × specific heat capacity × temperature change}$
• The specific latent heat is the energy required for a substance to change its state. The equation for specific latent heat is as follows: $\text{Energy for a change of state = mass × specific latent heat}$

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What is the particle model of matter?

The particle model of matter is a theory that describes how particles of a substance are arranged, and how they move.

What are the 5 points of the particle model of matter?

1. All matter is made up of particles.
2. All particles are in constant motion.
3. All particles within a single substance are identical.
4. Temperature affects the speed of movement of a particle.
5. In gases, there are spaces between the particles, but in solids and liquids, the particles are close together.

What are the limitations of the particle model of matter?

The main limitations of the particle model of matter are that there are no forces between the spheres of each object. On top of this, there is also the fact that atoms, molecules and ions are not solid spheres.

What is an example of a particle model of matter?

An example of the particle model of matter in real life is how water can go from a solid to a liquid and then to a gas. If water is cold enough it can become ice, and if it is boiled to a high enough temperature it becomes steam.

How the particle model of matter explains expansion and contraction?

The particle model of matter requires that particles remain the same size no matter what. However, the space between each of the particles changes. If a solid is heated, the particles vibrate more violently and therefore the solid expands outwards.

## Test your knowledge with multiple choice flashcards

A substance is melting. For the particles that comprise it, what type of energy is increasing?

In order for a substance to change from gas to liquid, we need to supply energy to it.

Is the temperature of a gas dictated ONLY by the energy of the particles in the gas?

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