Atomic models in the curriculum

Featured paper

Taber , K. S. (2003) 'The atom in the chemistry curriculum: Fundamental concept, teaching model or epistemological obstacle?', Foundations of Chemistry, 5, pp. 43-84.

It is no surprise that students in school hold alternative conceptions about ‘the atom'. This paper by Keith Taber discusses why students may acquire ideas about the atom that differ from modern scientific understanding. The key argument made in this paper is that these alternative ideas stem, in part, from the way atoms are presented in the school curriculum. The paper discusses how the concept of the atom met in the curriculum is not coherent and is based on historical models. 

For the full argument it is important to read the original paper as expressed by the author but a few key points that have influenced my work are summarised here. These relate to how the atom is described at different points in a typical chemistry curriculum and how the word 'atom' is used in teaching different age groups. The fact that these are not always the same is a reason that this paper is one I return to repeatedly. 

The concept of the atom that is often first presented to students is of atoms being the indivisible and forming the constituent particles of all substances. Elements are defined as being made up of ‘one type of atom’ in contrast with compounds which are made up of ‘two or more types of atom’. Chemical reactions are described as the ‘rearrangement of atoms’. The idea of an atom as indivisible is clearly a much older model of the atom than even more recent historical models. 

The paper suggests that students may continue to attribute to atoms the property of being indivisible and of forming the constituent particles of all substances even when a later model of the atom has been introduced. However this earlier indivisible model of the atom may still be referred to in teaching older students.  At age 14 to 16 students should understand that an atom is not indivisible because it is made up of sub-atomic particles but the term 'atom' may still be used to mean the more simple model when convenient. As students learn about structure and bonding, they should recognise that substances may be made up of ions or molecules rather than complete atoms. This concept is essential for further understanding for example to understand the concept of a mole. One mole of the substance oxygen is not one mole of oxygen atoms it is one mole of oxygen molecules.

In this paper Keith Taber coins the term ‘atomic core’ to refer to the nucleus of an atom plus the inner electrons and argues that very often, when the word ‘atom’ is used in the curriculum, it is actually an atomic core that is referred to. 

This idea of an 'atomic' core prompted to me to reflect on exactly what is meant when the term atom is used in teaching in a variety of scenarios. The questions below were inspired by this thinking.
 

Developing Understanding question

This question for the RSC’s Developing Understanding series asks students to think about what is represented in a diagram of the structure of diamond.

Diamond has a three-dimensional giant molecular structure.
The diagram below shows a representation of the structure of diamond.

a.    Which part of a carbon atom is represented by a line on the diagram?

A nucleus    
B shared pair of outer electrons
C nucleus and inner electrons
D inner electrons

b.    Which part of a carbon atom is represented by a circle?

A nucleus    
B shared pair of outer electrons
C nucleus and inner electrons
D inner electrons

Even though the circles in this sort of diagram would commonly be called atoms, they actually represent just the nucleus and inner electrons of each atom, or what Keith Taber referred to as the ‘atomic core.’
 

BEST Diagnostic Question

Comparing models

The diagnostic question checks whether students are able to compare the particle model and the atomic model.

 
A helium atom may be represented using the particle model and the atomic model.

Some students compare the two different models.
Who do you agree with, and why?

A student who agrees with Aaron is demonstrating an understanding that a model is not a direct reflection of reality. Agreement with Arush shows recognition that a model has a purpose and that in some cases a simpler model may provide a clearer explanation.

Reflective questions

How and when do you use the term ‘atom’ in your teaching?

What do you actually mean each time use use the term 'atom'?

Does your use of the term change with different phases of the curriculum?

Useful links

Developing Understanding: Carbon allotropes

A ramped student worksheet that aims to help students to deepen their understanding of carbon allotropes and to strengthen their mental models. 

Royal Society of Chemistry

 
BEST Topic 6 Key concept 1: Atomic model

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

University of York Science Education Group