“Why should I believe in atoms? I can’t see them.” Students ought to ask such questions, and teachers ought to seize the teachable moment.
“Because I [or the textbook, or some other authority, etc] said so” fails to take advantage of the teaching opportunity. It does not invite the student to learn to use the investigative methods of science, rather it simply closes off a discussion.
The statement “I can’t see them.” is true, as long as one accepts the student’s implicit assumption that seeing is accomplished only with the eyes. An alert teacher can use this as an opportunity to invite the student to participate in a richer world. Perhaps a better answer is to offer, in a comforting voice, “Do blind people believe in shoes?” Such a response can move the discussion toward ways in which we use other senses and inferences from many sources to create an object in our minds. How do we “see without seeing”?
Seeing with the mind is a skill, and many students have not yet worked with that skill. But students can practice, and with practice they can get better. Teachers can help them learn the skill.
Chemistry Chapter Zero provides approaches and materials to help students learn to “see without seeing.” Only a summary will be given here; the Teaching page provides more detail.
The teaching goal is that students will strengthen their ability to “see without seeing”. Having become more comfortable with that skill, they can more easily use indirect evidence for atoms and finally, accept that atoms are real.
How long does it take for students to learn to “see without seeing”? I offer the comment of a colleague who teaches sophomore organic chemistry: “I have to work so hard with models; it takes them a long time to be able to see reactions”.