Crystals and atomic models for beginners
Crystals encourage both teachers and students to ask questions. We should encourage the suggestion that some things must be arranged in a regular array inside crystals, things too small to see called ‘atoms'. Otherwise it is difficult to see why crystals make such regular shapes, and how they ‘know to make the same shape every time’.
(Of course professional crystallographers appreciate that the same material makes a great variety of shapes, as judged by the layman, although they all share the same fundamental pattern. To students, at their first careful look at crystals, the idea of some standard shape is likely to seem quite clear.)
Younger students will certainly have heard the word ‘atom’ but only some will know what it means. Though the word is used easily, most will not have reached the stage of wondering about things that are too small to see. So, the idea needs introducing gently.
When students have been given the idea of small particles or bits of which everything is composed, they are likely soon to take the idea of atoms for granted. So the question ‘How big are atoms?’ can be asked as something to wonder about while leaving it unanswered until more evidence has been gathered.
When introducing crystals to young students, molecules and ions are probably best left aside from the discussion.