Materials science introduction

Nature of science:

Improvements in technology—different materials were used for different purposes before the development of a scientific understanding of their properties. (1.8) Patterns in science—history has characterized civilizations by the materials they used: Stone Age, Bronze Age and Iron Age. There are various ways of classifying materials according to desired patterns. (3.1)

• Materials are classified based on their uses, properties, or bonding and structure.
• The properties of a material based on the degree of covalent, ionic or metallic character in a compound can be deduced from its position on a bonding triangle.
• Composites are mixtures in which materials are composed of two distinct phases, a reinforcing phase that is embedded in a matrix phase.

Applications and skills:

• Use of bond triangle diagrams for binary compounds from electronegativity data.
• Evaluation of various ways of classifying materials.
• Relating physical characteristics (melting point, permeability, conductivity, elasticity, brittleness) of a material to its bonding and structures (packing arrangements, electron mobility, ability of atoms to slide relative to one another).

• What materials were used by ancient civilizations, such as the Aztecs, Romans, and Chinese? Even though these ancient civilizations were located in geographically diverse locations, the materials they used were similar.

Theory of knowledge:

• Although it is convenient to classify materials into categories no single classification is “perfect”. How do we evaluate the different classification systems we use in the different areas of knowledge? How does our need to categorize the world help and hinder the pursuit of knowledge?

Utilization:

• Syllabus and cross-curricular links:
• Topic 4.2—the role of electronegativity in bonding types

• Permeability to moisture should be considered with respect to bonding and simple packing arrangements.
• Consider properties of metals, polymers and ceramics in terms of metallic, covalent, and ionic bonding.
• See section 29 of the data booklet for a triangular bonding diagram.

• Aims 1 and 3: Investigation of tetrahedra of structure and bonding types and where covalent networks and polymers fit on these diagrams.
• Aim 6: Experiments could include investigating the stretching of rubber bands under different chemical environments, or properties of metals, polymers, ceramics, or composites, making thin concrete slabs from various ratios of cement, gravel, and sand and investigating the breaking strength upon drying.