Unit:Crystals

Lesson Topic/Theme: Unit Cell Classification

Overview:Students will study 6 basic unit cell structures.In groups, they will construct paper models of 6 basic crystalline unit cells. (Note:Even though this activity is focused on 6 unit cell types, there are 7 basic unit cell structures: cubic, tetragonal, orthorhombic, trigonal, hexagonal, monoclinic, and triclinic)

Keywords:cubic, hexagonal, tetragonal, monoclinic, triclinic, orthorhombic, unit cells, symmetry, parallelism, acute and obtuse angles

Learning Objectives:By completion of this unit on crystal structure, students will be able to:

1.identify 6 basic unit cell structures (cubic, hexagonal, tetragonal, monoclinic, triclinic, orthorhombic) by shape and symmetry after completing a geometric construction exercise.

2.indicate the parallel sides of the unit cells as well as the differences in the angles of these unit cells.

Assessment Tool and Scoring Criteria

1.Students will be expected to correctly name and identify all 6 unit cells from the side length and angle data they collect from the constructions.

2.Students will be asked to identify a unit cell on an oral/written quiz if the teacher holds up a model or from diagrams presented on a page.

3.Scoring Criteria:

Advanced:The student is able to accurately identify all 6 of the basic unit cell structures, siting angles and identifying the sides of the unit cells that are parallel.

Proficient: The student is able to accurately identify 5-6 of the basic unit cell structures.

Basic:The student is able to accurately identify 4 of the basic unit cell structures.

Below Basic:The student is able to accurately identify less than 4 of the basic unit cell structures.

Materials: 

1.unit cell construction model cut-outs 

Borgford, Christie L., Lee R. Summerlin, Chemical Activities, American Chemical Society, 1988 47-49.

2.models of unit cells (VWR Scientific)

3.scissors, metric rulers, tape, protractors

Procedure:

1.Pass out model construction papers to groups of 3.

2.Have students construct the models without the names of the unit cells.

** Make sure to white out the names before you photocopy.

3.Have students measure the lengths of sides and angles of each unit cell.

4.Present the models and discuss the angles and name each model.

5.Have students try to correlate their constructions to the appropriate models.

Correctives:

1.Students will “pair and share”. The students will pair and gather information on a unit cell type and present it to the class.

2.One-on-one tutoring with teacher before or after school.

Extensions:

1.Students will construct large and colorful, geometrically correct models of unit cells for classroom display.

2.Students will perform the second lesson in this unit experimenting with crystal growth.