The main mathematical topics in 7th grade (taken from the Common Core Standards) are:

(1) developing understanding of and applying proportional relationships

(2) developing understanding of operations with rational numbers and working with expressions and linear equations

(3) solving problems involving scale drawings and informal geometric constructions, and working with two- and three-dimensional shapes to solve problems involving area, surface area, and volume

(4) drawing inferences about populations based on samples

* These are general overviews.  For more specific standards, follow the "Common Core Learning Standards" link on the left.