Chemical Formulas

• Law of Definite Proprotions: Different samples of a compound always contains the same elements in the same mass ratio- regardless of sample size.

Ex: every sample of CO2 has the O/C mass ratio(2.66:1)- no matter the amount.

• Law of Multiple Proportions: If two elements form more than one compound together, the masses of one element combine with a fixed mass of the other are in ratios of small whole numbers.

Ex. CO2 has exactly twice the O/c mass of CO. The ratio 2.66 divided by 1.33=2- a small whole number.

• Molecule- a combination of at least two atoms in a specific arrangement, held together by chemical bonds. They can elemental or a compound

• Diatomic Molecules are molecules made of exact two atoms. Must memorize H2, N2, O2, F2, Cl2, Br2,I2. In reactions, always write these as diatomics-never as a single atoms.

• Polyatomic= more than 2 atoms

• Allotropes=different structural forms of the same element (eg. diamond and graphite)

• Subscripts in a molecular formula tell you the exact atom count. No subscript=1 atoms(implied)