Aseel Samaro

Using Particles Models

You have learnt that the particle model is a ‘good enough’ model for explaining most changes of state.

How good is it at explaining other phenomena and observations related to physical and chemical changes?

Introduction

You may remember using different separation techniques like:FiltrationChromatographyDistillation

The particle model can be used to explain how these work, but some adaptations may be needed because it has some limitations.

Explaining separation processes

The particle model cannot:1. distinguish between different types of particles, unless they are

given different colours2. show what kinds of atoms are in the molecules3. show different intermolecular forces between particles.

The particle model needs to be adapted to explain particular phenomena – so it can be a ‘good enough’ model.

This figure shows the process of distillation, which separates liquids. The particle model has been adapted to explain distillation

How has the particle model been adapted to make it a ‘good enough’ model?

Use a ‘good enough’ model to explain how filtration work

How has the particle model been adapted to make it a ‘good enough’ model?

The alcohol particles have been given a different colour; so they can be distinguished from the water particles; to see what is happening to the alcohol particles.

Use a ‘good enough’ model to explain how filtration workParticles of the liquid should be smaller than the particles of the solid. The explanation

should show that the particles of the liquid go through the gaps in the filter paper, but the particles of the insoluble solid are too big to pass through.

It is clear that some substances are more soluble than others.

As it stands, the particle model is not a ‘good enough’ model to explain this and needs adapting.

Solute particles have forces of attraction between themselves and between the solvent particles.

When the forces of attraction between the solute and solvent are stronger than between the solute particles, then the solute will dissolve.

Explaining solubility

The solute particles fill the spaces between the solvent particles.

When all the spaces are filled up, the solution is said to be saturated, because no more solute can be dissolved.

If the temperature is increased, the solvent particles move with more energy, moving further apart and creating more space.

More solute can be dissolved at the higher temperature because as there are more gaps that can be filled.

Adapt the particle model to explain why some solids are more soluble than others.

Diagram should show stronger solute–solute forces between less soluble solutes; and stronger solute–solvent forces for more soluble solutes

Can the particle model be used to show how temperature affects solubility? What are the strengths and limitations of the model?

Diagram should show more spaces at higher temperatures; so more solute particles can fill the spaces.

Strengths –shows why more solute can be dissolved; at a higher temperature. Limitations – does not show that the particles have more energy at a higher

temperature.

When calcium carbonate is added to hydrochloric acid, a gas, carbon dioxide, is formed. A chemical change takes place.

Models that involve representations of the atoms must be used to explain this.

Notice that the same number of atoms must be on both sides of the equation, ensuring that mass is conserved.

Explaining Chemical changes

Common elements Colour for atom

hydrogen white

oxygen red

carbon black

chlorine green

nitrogen blue

bromine brown

sulfur yellow

iodine purple

metals, e.g. sodium, calcium grey

Colours for elements in the particle model

This shows a ‘good enough’ particle model to demonstrate the changes when calcium carbonate is added to hydrochloric acid

Use particle model colours from the table to show what would happen when magnesium metal is added to hydrochloric acid (HCl), making magnesium

chloride (MgCl2) and hydrogen (H2). Write a word equation for the reaction first. Think about the conservation of mass.

Lead nitrate (Pb(NO3)2) solution reacts with potassium iodide (KI) solution to make lead iodide (PbI2) and potassium nitrate (KNO3). Write a word equation

for the reaction. Think about the conservation of mass and use a particle model to show the reaction.

Activity !

Evidence for the existence of particles began to emerge in the 1800s.

We have come to understand so much more about particles that we have very different models

Did you know…?

Thank you