The National Science Digital Library has a wealth of high quality digital resources to teach almost any topic in K-12 math and science.  Following is a sample of 20 exemplar NSDL links specific to teaching atomic structure at the K-12 level.
The History of the Atom

Atomic Structure Timeline  This site explores discoveries related to atomic structure including the electron, […]

The National Science Digital Library has a wealth of high quality digital resources to teach almost any topic in K-12 math and science.  Following is a sample of eleven NSDL links to more than 10,000 resources specific to teaching math at the K-12 level.
To browse resources by standards or domains
1. The NSDL Math Common Core collection has math interactives and […]