One of the most difficult concepts for my students to understand is the difference between atoms and elements. They also struggle to understand the differences between atoms of different elements.
I use this activity -- which asks kids to identify easy to understand definitions of atoms and elements and to draw/find a picture of atoms of two different elements -- to introduce these ideas.
The most powerful part of this lesson is watching groups of students rate and rank different definitions of atoms and elements in order to determine which should be included on their handout. The discussion between students is where the real learning happens as kids work to understand the terminology and to determine which online definition explains the terminology in the most approachable way.
The preview version of this activity is an uneditable PDF. The for purchase version is a Word Doc that can be customized.