1. Elements & compounds

2. Chemist classify pure substances based on the particles they are made of.
Pure Substances are classified as Elements or Compounds
ELEMENTS:
A pure substance that cannot be broken down into simpler substances
109 elements have been isolated and identified, 91 are naturally occurring
Elements are identified by their name, symbol and atomic number

3. Examples: Elements are the building blocks of all substances.
A pure substance composed of two or more different elements in a fixed bond is called a Compound
They can be broken into elements by chemical means
Examples:
Name: Hydrogen, Symbol: H, atomic #: 1
Name: Water, Symbol: H2O