Hard Diamonds
Phenomenon:
Diamonds are the hardest material in the world. A diamond can only be cut with another diamond. Contrast this with your pencil lead which is soft enough to write with.
Student Task:
Construct an explanation for what causes a diamond to be so hard and a pencil lead to be so soft.
Model
Students develop a model to describe the atomic structure of pencil lead and diamonds.
Investigate
Students compare and contrast the observable properties of pencil lead and diamonds.
Obtain Information
Students read to obtain information about patterns in the atomic structure of solids (called crystals).
Analyze Data
N/A
Explanation:
Graphite and diamonds have very different properties (e.g., hardness) due to the arrangement of carbon atoms in three-dimensional space. In graphite, the carbon is arranged to form 2D hexagons in sheets. In diamonds, the carbon is arranged to form 3D tetrahedrons. This makes diamonds the hardest material on Earth.
NGSS Standard:
MS-PS1-1. Develop models to describe the atomic composition of simple molecules and extended structures.
[Clarification Statement: Emphasis is on developing models of molecules that vary in complexity.]
Utah SEEd Standard:
6.2.1 Develop models to show that molecules are made of different kinds, proportions and quantities of atoms.
Recommended Teaching Sequence:
Day 1:
Compare and contrast the observable properties of pencil lead and diamonds.
Read to obtain information about patterns in the atomic structure of solid crystals.
Day 2:
Develop and use a model to describe the atomic structure of pencil lead and diamonds.
Construct an explanation for what causes a diamond and graphite to have different properties.
Formative Assessment:
Use what students have written in their science notebooks as a formative assessment, including their written explanation for the phenomenon. Do students understand that solid matter is made of atoms and molecules that are fixed in place? Do they understand that the behavior of a substance (property of a material) is connected to its atomic structure?
Lesson Contributor:
April Mitchell, Science Coach, Salt Lake City School District