1. Notes: Formulas and Equations
Physical change – does not result in a new identity or composition of the matter; chemical formula does not change.
Chemical change – results in the formation of a new substance with different properties, Chemical formula will change.
Another term for a chemical change is a chemical reaction. Chemical reactions change the arrangements of the atoms in the compounds and formulas.

2. All substances can be represented by a chemical formula – a shorthand way of writing chemical names.
Subscripts (small # below symbol) give the correct ratio of atoms. 3
Coeffecient- (Large # in front of formulas) gives the number of molecules of a compound or number of elements.

3. A chemical equation is a description of what happens in a chemical reaction.
The substances one starts out with in a chemical reaction are the reactants.
The new substances made by the reaction are the products.
The arrow (  ) is called the yield sign. It separates the formulas of the reactants and the products. It also indicates the direction that the reaction is taking place.

4. Example: Ar, He, O2, N2, H2, S8, P4, O3 Element
One type of atom either in groups
bonded together or not
Molecule
Groups of atoms bonded together
Compound
Groups of atoms with more than
one type of atom bonded together
Example: Ar, He, O2, N2, H2, S8,
P4, O3
Example: O2, N2, H2, S8, P4, O3,
Water (H2O)
Example: Water (H2O), Table salt
(NaCl), Hydrogen Mono-chloride
gas (HCl)
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