This document discusses elements and atoms. It defines an element as a substance made up of only one type of atom. Elements have unique properties based on the type and arrangement of their atoms. Atoms are made up of protons, neutrons, and electrons. The document outlines some of the first elements discovered and notes that over 100 elements have now been identified. It discusses how elements are represented by chemical symbols and arranged in the periodic table based on their atomic structure and properties. Compounds are formed when elements combine and take on new properties different than the individual elements.