The particle model

Featured article

Johnson, P. (1998). Progression in children’s understanding of a ‘basic’ particle theory: A longitudinal study. International Journal of Science Education, 20 (4), pp.393–412.

Very often students will get asked to label a particle diagram or to draw the particle diagram for a given state, however this paper suggests that even if answering ‘correctly’ students may hold a range of misconceptions.

The particle model under discussion in this paper is described as a model with sufficient detail to account for the characteristic properties of the three states of matter. It is not, the author specifies, a model that distinguishes between the types of particle (atoms, molecules and ions). 

The author summarises the common findings of the existing literature about student understanding of the particle model, identifying five areas of difficulty:

1. The relative spacing between particles in the three states.

Showing the spacing between particles in the liquid state as intermediate between the solid and gas states.Typical diagrams for the gas state underrepresent the relative spacing of particles.

2. The intrinsic motion of particles

Many students showed little appreciation of the intrinsic motion of particles.

3. Ideas of forces of attraction between particles

Very few students used the idea of forces of attraction between particles.

4. The ‘space’ between particles

The idea that there is ‘nothing’ between particles seemed to cause a lot of difficulties for students. Some preferred to think that something must be there (often referring to this as ‘air’).

5. The nature of the particles themselves

Many students were found to give particles the same properties as the bulk material. For example, a copper atom was thought to have the same properties as copper metal.

The paper reports on a three-year longitudinal study following a cohort of pupils in a non-selective English secondary school as they moved from year 7-9 (ages 11 to14). Students were periodically interviewed following teaching of four planned unit designed to develop the idea of a chemical substance.

The responses were used to identify four distinct particle models held by the students.

Model X: Substances are continuous (and not made of particles).

Model A: Particles are found in the continuous substance.

Model B: Particles are the substances, but with the macroscopic character of the bulk substance.

Model C: Particles are the substance and the properties of the substance in a given state are a collective property of those particles.

The interview questions enabled the author to identify the model of thinking held by students at the time of the interview. Whilst there were some students were inconsistent and applied different models in different circumstances, the majority had complete models of either X, A, B or C. This method of categorisation enabled the author to explore how student thinking about the particle model changed over time.

In general, many students were found to progress in the model that they were using. The author identified two different ‘dimensions’ of this progression: a continuous to particulate dimension and a macroscopic to collective properties dimension.

BEST Diagnostic question

Imagine you could see the particles in a jar of methane gas.

Which diagram best matches what you would see?

 

The correct answer is C.

Reflective questions

When teaching the particle model, do you teach what is between the particles? How do/could you explain the concept of ‘nothing’ to students?

It is not uncommon to refer to the ‘particles in a solid’. To what extend could this language reinforce existing misconceptions and how could the language be changed to avoid this?

An atom is often defined as ‘the smallest particle of an element’. To what extent could that reinforce earlier misconceptions about the particle model? How could this be mitigated?

Useful links

BEST Topic 1 Key concept 1: Particle model for the solid, liquid and gas states

Diagnostic questions to check for student misconceptions about the particle model as part of a five-part progression (and including response activities)

University of York Science Education Group

Developing understanding: States of matter

A ramped student worksheet that aims to help students to deepen their understanding of the particle model and to strengthen their mental models.

Royal Society of Chemistry

Acknowledgements

The example BEST diagnostic question was developed by Helen Harden (UYSEG), from an idea by Andrew Hunt selected from a collection of ASK items devised for research by Philip Johnson (Durham University).

The particle model image is from the RSC Johnstone's Triangle Resource: States of Matter