Particle Model of Matter

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.

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.

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$(\mathrm{kg}/{\mathrm{m}}^3)$,$m$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.

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.

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.

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$(J/kg°C)$
• $∆\theta$is the change in temperature, measured in degrees Celsius$(°C)$

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.

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.