8th grade Science Chemical formulas and equations

Compounds and bonding Compound-a substance that is composed of atoms of 2 or more different elements chemically combined Ex: NaCl—sodium chloride (salt) *sometimes the properties of the compound are different than of the individual elements

Chemical formula A chemical formula uses chemical symbols and numbers to represent a given substance The chemical symbols in a chemical formula tell you what elements make up a substance Subscripts—numbers written below and to the right of chemical symbols. They tell how many of each type of atom are in a molecule Coefficients-large numbers in front of chemical formulas They tell how many of each compound you have

Chemical equations A chemical equation is an expression that uses symbols to show the relationship between the starting substances and the substances produced by a chemical reaction Reactants—substances that begin the reaction (always on left side of the arrow) Products—substances formed by the reaction (always on right side of the arrow)

Chemical equations Arrows-known as a yield sign points from the reactant to the product Law of Conservation of Mass: states matter is neither created nor destroyed in ordinary chemical and physical changes. Because of this law, we can BALANCE equations (what is found on one side of the arrow in an equation must be equal to the other side of the arrow

Steps to Balancing Equations Identify the reactant Identify the product List the atoms present on the reactant side, one under another List the atoms present on the product side, one under another Count atoms on both sides-if numbers are equal, the equation is balanced If not, ADD COEFFICIENTS in front of atoms to balance the equations

More balancing rules You cannot add coefficients in the middle of a compound You cannot change subscript numbers-this changes what the compound/molecule actually is Pay attention to parentheses—(these apply just like in math)