Chemical elements are substances composed of only one type of atom and they cannot be broken down further. Chemical elements are the simplest forms of matter and each one is assigned a specific atomic number. Check out these articles on chemical elements.
How the Periodic Table Works
It begins with an unassuming "H" and ends in crazy elements that you've likely never heard of. But the periodic table, encapsulated on a mere sheet of paper, can be a scientist's best friend and a testament to our human drive to organize the world.