Atomic Theory MATTER Mixtures Pure Substances Physical Change Mechanical Mixtures Solutions Compounds Elements Chemical Change Pure Substances • Pure substances can be divided into 2 groups: Compounds and Elements. • Compounds are pure substances that are made up of two or more different elements. • Elements in a compound are chemically bonded to each other and exist in a specific ratio that is always the same. • Ex: H2O Elements • An element is a pure substance made up of one type of particle, or atom. • Each element has it’s own properties and cannot be broken down into simpler substances by means of chemical change. Atoms • Atom: All matter is made up of atoms. Atoms are the smallest unit of an element that maintains the properties of that element. • http://www.brainpop.com/science/m atterandchemistry/atoms/ Compounds and Molecules • Molecule: Composed of 2 or more elements that are joined by chemical bonds. • The elements in a molecule can be the same (H2, O2) or the elements can be different. • All compounds are molecules, but not all molecules are compounds!! Compounds and Elements • The properties of a compound are different than the properties of the elements that make it up. Dalton’s Atomic Theory 1. All matter is made up of small particles called atoms. 2. Atoms cannot be created, destroyed, or divided into smaller particles. Dalton’s Atomic Theory 3. All atoms of the same element are identical in mass and size, but are different in mass and size from other elements. 4. Compounds are created when atoms of different elements link together in definite proportions.