Lee Chu YemChemistry Chapter 4 Summary Relative Isotopic Mass (Ir) Mass of an isotope compare to the mass of 12C

Obtained using mass spectrometer

ChlorineRelative Atomic Mass (Ar) Weighted average of the relative masses (Ir) of the natural occurring (%) element on the 12C scale

Atomic mass

Relative Molecular Mass (Mr) Mr of a compound is the mass of one molecule relative to the mass of 12C 12C = 12 SUM OF Ar Molecule: a group of 2 or more atoms of non-metallic elements

KCl = non-molecular compound has both metallic and non-metallic Relative Formula Mass is used for non-molecular compounds

Avogadro Constant (NA) 6.02 x 1023 atoms= 1 mole = 12g of 12CThe Mole 1 mole = number of specific particles in a substance that is exactly 12g of 12C the particles can be: atoms molecules ions examples: 1 mole of hydrogen atoms contain NA hydrogen (H) atoms 1 mole of glucose molecules contains NA glucose (C6H12O6) molecules

N

n=

NA

Molar Mass (M) 1 mole of an element or compound Diff particles = diff mass of 1 mol Relative atomic mass of an element express in grams Unit = g mol-1 Ar = Mr in g = 1 mol in g

M(CO2) = 44g mol-1: The molar mass of carbon dioxide is 44g mol-1 1 mole of carbon dioxide has a mass of 44g 6.02 x 1023 molecules of carbon dioxide have a mass of 44g

N Mr

M=

Percentage Composition

Empirical Formula Simplest whole number ratio of atoms present Determined by experiments

Molecular Formula Actual numbers of atoms in molecule