http://education-portal.com/academy/lesson/early-atomic-theory-dalton-thompson-rutherford-and-millikan.html
http://education-portal.com/academy/lesson/what-are-elements.html
http://education-portal.com/academy/lesson/atomic-number-and-mass-number.html
http://education-portal.com/academy/lesson/the-periodic-table-properties-of-groups-and-periods.html