Atoms (Section 1b)

Movement of Particles

1.4 describe and explain experiments to investigate the small size of particles and
their movement including: i) dilution of coloured solutions, ii) diffusion experiments

i) Dilution

Dilution is the process of a substance being put into a solvent in order to reduce it's concentration. 

The dilution of Potassium Manganate (VII) solution

1) Potassium Manganate (VII) is a bright purple substance. It is a good example of dilution because the process itself is very easy to see. 
2) If you add water to the purple solution, the potassium managanate (VII) particles will spread further apart.
3) You will see the solvent becoming less and less purple once you've added water.
4) The more water you add, the more the solvent will dilute, and the less and less purple it will become. 

Showing the colour change of Potassium Manganate (VII) before, during, and after dilution. 

ii) Diffusion

Diffusion is the gradual movement of particles from an area of high concentration to an area of low concentration. 

The diffusion of bromine gas and air 

1) Bromine gas is a brown, strong smelling gas. It is a good example of demonstrating diffusion in gases.
 2) Fill half a gas jar full of bromine gas, and fill the other half with air. Separate the two gases with a glass plate between them.
 3) When you remove the glass plate, you will be able to see the bromine gas slowing diffusing through the air.
 4) Because of the random motion of particles in a gas, the bromine will eventually diffuse completely through the air. 

1.5 understand the terms atom and molecule

Atom = A unit of matter made up of a nucleus, protons, and orbiting electrons. 

Molecule = A group of two or more atoms held together by covalent bonds. 

1.6 understand the differences between elements, compounds and mixtures

Elements = Consist of one type of atom only. They cannot be broken down into a simpler type of matter by any means, either physical or chemical. They can exist as either atoms or molecules. Examples include; nitrogen, copper, and oxygen.

Compounds = A substance made up of two or more different elements which are chemically joined together. They can be broken down into a simpler type of matter (elements), but only by chemical means, not physical means. They are often very different from the properties of the original elements. Examples include; carbon dioxide and iron sulfide. 

Mixtures = Mixtures consist of two or more different elements or compounds that are physically joined. Because of this, they can be separated by physical means, not chemical means. Unlike compounds, mixtures often retain many of the properties of it's components. The properties of a mixture are therefore a mixture of the properties of it's separate parts. Examples include; the air and crude oil. 

Changing States of Matter

1.2 understand how the interconversions of solids, liquids and gases are achieved
and recall the names used for these interconversions.

                      

1.3 explain the changes in arrangement, movement and energy of particles
during these interconversions

Solid > Liquid
This is achieved through a process called melting. The solid is heated, causing it's particles to gain more energy and vibrate. This weakens the forces that hold the solid together, making the solid expand. At a certain temperature (it's melting point), the particles will have enough energy to break free from their positions and thus the solid turns into a liquid. 

Liquid > Solid
This is achieved through a process called freezing, or solidifying. In this process, heat is removed. When a liquid is cooled, the particles lose energy and slow down. They eventually stop moving, apart from vibrating in their fixed position. A solid has now been formed. 

Liquid > Gas
A liquid becomes a gas through a process known as evaporating. In this process, heat is supplied. When a liquid is heated, the particles gain more energy and this causes the particles to vibrate/move faster. This weakens and breaks the bond holding the liquid together, as the particles break away from eachother and expand (this will happen at a certain temperature). The liquid has now become a gas. 

Gas > Liquid 
The process of turning a gas into a liquid is known as condensing. Like freezing, within this process heat is removed. When you cool a gas, the particles will lose energy. This loss in energy causes the particles to move at a much slower pace as they move closer together. Eventually, the particles will no longer have sufficient energy to move away as they bump into one another, and when this happens, the gas has become a liquid.

Solid > Gas 
A solid becomes a gas through a process known as sublimation (subliming). Sublimation refers to a solid becoming a gas , without becoming a liquid during this process. These reactions occur at temperatures and pressures below the triple point, ("the particular temperature and pressure at which the solid, liquid, and gaseous phases of a given substance are all at equilibrium with one another.") This means that the particles will have too much energy to remain in a liquid state and will instead become a gas. 

Gas > Solid 
A gas becomes a solid in a process known as deposition. This process refers to a gas becoming a solid, and like sublimation, not going through a liquid phase in the process. This occurs when the temperature or pressure is below the triple point, and therefore the particles will have too little energy to move around and remain in liquid form, so they form a solid. 

                                                                 

States of Matter

States of Matter

The three states of matter are; solid, liquid and gas. These are the three different forms that materials come in. The state, or form, of the material depends on the strength of the forces of attraction between the particles of the material. This force is determined by three things; 

• the material
• the temperature
• the pressure. 

1.1 understand the arrangement, movement and energy of the particles in each of the three states of matter: solid, liquid and gas 

Solids 

a) Solids have very strong forces of attraction between their particles, which is why they are held so closely together in fixed positions, as shown in the diagram. They form a very regular lattice arrangement.

b) The particles do not move from their positions. Solids keep a definite shape and volume at all times because of this. 

c) When heated, the particles in a solid will vibrate about their positions. This causes solids to expand slightly when heated, and can lead to the solid melting to become a liquid. 

Liquids

a) Liquids have a weaker force of attraction between it's particles than solids. The particles are randomly arranged and are able to move past each other, however they tend to stick close together, as shown in the diagram above. 

b) Liquids will always have a definite volume, but not always a definite shape. For example, if a liquid was poured into an empty container it's volume would remain the same, but the shape would not, and it would instead change to the shape of the container. 

c) The particles within a liquid are constantly moving with random motion. When heated, the pace at which these particles move increases and this causes the liquid to expand slightly. This can lead to a liquid evaporating to become a gas. 

Gases

a) Gases have a very weak force of attraction between it's particles. The particles are free to move around and are far apart, just like in the diagram above. Additionally, the particles in gases always travel in straight lines. 

b) Gases do not keep a definite shape or volume. They will fill any container they are put into.

c) Like in a liquid, the particles in a gas move constantly with random motion. When heated, the pace at which the particles travel is increased, leading the gas to either expand when heated, or to have it's pressure increased.