2. A COMPOUND is a pure substance composed of two or more elements that are chemically combined.

3. Table salt (NaCl) – sodium and chlorine Water (H 2 O) – hydrogen and oxygen Sugar (C 6 H 12 O 6 ) – carbon, hydrogen, and oxygen Carbon dioxide (CO 2 ) – carbon and oxygen Baking soda (NaHCO 3 ) – sodium, hydrogen, carbon, and oxygen

4. Compounds are NOT random combinations of elements. When a compound forms, the elements join in a specific ratio. For example, H 2 0 is water, but H 2 O 2 is hydrogen peroxide!

5. Elements Combine to Form Compounds 2 hydrogens + 1 oxygen = H 2 O (water) Sodium + Chlorine =NaCl Table Salt

6. Each compound has a unique set of properties that allows you to distinguish it from other compounds. Each compound has its own physical properties (boiling point, melting point, density, color, etc.). Compounds can also be identified by their chemical properties (reactivity).

7. A compound has different properties from the elements that form it. For example, sodium (Na) is a shiny metal that reacts with water, oxygen (O 2 ) and hydrogen (H 2 ) are flammable gases. However, sodium hydroxide (NaOH) is a strong base that has many uses including soap making and glass etching.

8. Compounds can be broken down into simpler substance through chemical changes. For example, when you open a can of Pepsi, the carbonic acid breaks down into carbon dioxide and water. Compounds cannot be broken down by physical changes.

9. Element or Compound? MgCl 2 KOHHeZnCOCoHCl Compound Element Compound Element Compound