Explain the difference between an element and a compound. Distinguish between a substance and a mixture. Identify the chemical symbols of elements, and name elements, given their symbols.

 Substances can be classified as elements or compounds.  An element is the simplest form of matter that has a unique set of properties. Cannot be broken down into simpler substances.  EX: H or Ne  A compound is a substance that contains two or more elements chemically combined in a fixed proportion. Can be broken down into simpler substances.  EX: H₂O, NaCl

 Compounds cannot be broken down into simpler substances by physical means.  A chemical change is a change that produces matter with a different composition than the original matter.

 The properties of compounds are quite different from those of their component elements.

 Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.  Chemical symbols are one or two letters. First letter is always capitalized, second letter is always lower case. EX: He, Mg, Mn  Some symbols come from the Latin name.  EX: Sodium, Na, natrium  Gold, Au, aurum  Iron, Fe, ferrum  Lead, Pb, Plumbum

 Formulas have element symbols and numbers  Subscripts in chemical formulas are used to indicate the relative proportions of the elements in the compound. EX: H₂O

Describe what happens during a chemical change. Identify four possible clues that a chemical change has taken place. Apply the law of conservation of mass to chemical reactions.

 The ability of a substance to undergo a specific chemical change is called a chemical property.  Chemical properties can only be observed only when a substance undergoes a chemical change.  During a chemical change, the composition of matter always changes.  A chemical change is also called a chemical reaction.

 One or more substances change into one or more new substances during a chemical reaction.  A substance present at the start of the reaction is a reactant.  A substance produced in the reaction is a product.

 Possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a solid.  Sometimes these clues may be the result of a physical change (bubbles forming from water and soap mixing together)  A precipitate is a solid that forms and settles out of a liquid mixture.

 During any chemical reaction, the mass of the products is always equal to the mass of the reactants.  The Law of Conservation of mass states that in any physical change or chemical reaction, mass is conserved. Mass is neither created not destroyed.