Is there a chapter on sound waves in science for a 6th/7th grader?
There is in the textbook we use for our 7th graders. We use the Holt Technology and Science textbook, and it has a portion of the text dedicated to the study of both sound and light. Thumb through the textbook your school is using, see if there is a chapter on sound, light, or maybe both combined, as it is in my school's textbook. A quick way to find out would be to go to your textbook's table of contents and go through the content of the textbook. You will be able to find out very quickly whether the content on sound is there or not.
If there is not, the internet abounds in articles and information on sound. The link I provided for you below is from the internet, and provides some very good information and links on the subject of sound.