Middle School Chemistry is a nice site with lessons and activities for grades 6-8. It also a Spanish version
The Physics Classroom has branched out, and now includes a section on Concept Builders for chemistry
Ted-Ed has a lesson for each element in the periodic table. Each lesson has a video at its core.
Stetson University has several online games for learning chemistry. They're also available for Apple and Android devices.
Understanding Science: How science really works has resources for teachers
The ChemCollective is a collection of virtual labs, scenario-based learning activities, tutorials, and concept tests for teaching and learning chemistry
Creative Chemistry has worksheets and teaching notes for fun activities suitable for a chemistry club, and around three hundred pages of question sheets and practical guides for GCSE and A Level Chemistry.
You will also find fun chemistry puzzles, interactive revision quizzes and molecular models.
AUS-e-TUTE is a science education website being developed by experienced science teachers to provide students and teachers with high quality, relevant, teaching and learning resources. It does require a paid sub to access most of the resources, but there are free chemistry tutorials