Video
This video can be used as alternate Lesson Hook/Minds On to demonstrate the opposite reactions of bonds breaking and bonds forming. This can be followed by a brief discussion question to get students thinking.
Crystals: A Handbook for School Teachers
The button below links to a PDF that is a guide for making crystals in the classroom. This is another alternative to a Lesson Hook as opposed to showing the video above. The teacher can perform the demonstration shown in the video to students or even have students do it themselves.