Metallic bonding models

Featured paper

Cheng, M. M. W. and Oon, P.T. (2016). Understanding metallic bonding: Structure, process and interaction by Rasch analysis. International Journal of Science Education, 38(12), 1923-1944.

 

The authors categorise three ways in which students think about metallic bonding.

1.      As a structure – a lattice arrangement of cations (positive ions) and delocalised electrons

2.       As a process – metal atoms losing outer electrons to form a ‘sea of electrons’

3.       As an interaction – a lattice arrangement of cations held together by electrostatic attractions between    these positive ions and the free electrons

The study aimed to test if structure, process and interactions were at increased levels of understanding. 3006 year 10-12 students in Hong Kong took part in the research survey.

The research study supported an order of difficulty where thinking of metallic bonding as an interaction was the model that was the most difficult:

interaction > process > structure

In Year 7-9 in Hong Kong a ‘particle model’ was used. This describes metals as being made of particles with each metal being made of one kind of particle. Changes of state were explained as a change in arrangement of these particles, but forces of attraction are not considered.

From Year 10 a ‘free electron’ model was used in which metals are made of a lattice of positive metal ions with delocalised electrons moving around them. This structure is held together by an all-directional electrostatic force.

When students are taught the initial particle model in this curriculum the focus of thinking is on structure. Later, to fully understand the ‘free electron model’ students must move to thinking in terms of interactions. The authors suggest that this shift is a challenge for students. Some students may remain thinking in terms only of structure. Consequently, they may not fully gain an understanding of metallic bonding as a form of electrostatic interaction.

Reflective questions

In your curriculum, does the initial particle taught at age 11-14 include the idea of forces of attraction between particles? What are the benefits and drawbacks of including this concept from the outset?

Are your students able to select and justify their choice of the most appropriate model to explain different properties of metals such as malleability and electrical conductivity?

Useful resources

Developing Understanding: Metallic bonding  

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

Royal Society of Chemistry

BEST Topic 7 Key Concept 1: Metallic structure model

Diagnostic questions to check for student misconceptions about metallic bonding as part of a five-part progression with additional response activities.

University of York Science Education Group