Chemical Composition … Moles Chemistry Mr. Lentz

Standards Addressed D Apply scale as a way of relating concepts and ideas to one another by some measure A Explain concepts about the structure and properties of matter.

Unit Topics 1. Atomic mass 2. Mole definitions 3. Percent composition 4. Empirical formulas 5. Molecular formulas

Some Definitions Atomic particles: Atomic number: Mass number: Isotopes: Atomic mass: –Mass spectrometer …

Atomic Mass May be better described as an average atomic mass … Carbon has two common isotopes … C-12 … 99.89% (.9989)(12) = C-13 … 1.11% (.0111)(13) =

Atomic Mass Actual masses of elements … –Hydrogen = 1.66 X g –Carbon = 1.99 X g –Oxygen = 2.66 X g Atomic Mass Scale (amu) –Hydrogen = 1.0 amu –Carbon = 12.0 amu –Oxygen = 16.0 amu

Problem There is no easy way to measure the mass of one atom Solution … –Change amu to grams –Determine how many atoms are in g of Carbon –Give this number a name

Avogadro’s Number Is the number of atoms in g of carbon Is equal to 6.02 X OR602,000,000,000,000,000,000,000.

The Mole Scientists gave Avogadro’s number of things a name … a MOLE

One Mole 1 mole of marbles would cover the earth 50 miles deep 1 mole of grains of sand would cover the US 1 cm deep Could you count to Avogadro’s number?

Moles Defined 1 mole = X “things” 1 mole = mass in grams (usually called molar mass)

Molar Mass Units … grams / mole For elements … it is the atomic mass in grams For compounds … it is the sum of the masses of the elements present

Molar Mass What is the molar mass of copper? answer = 63.6 g What is the molar mass of water? H 2 O H (2)(1.0) = 2.0 O (1)(16.0) = 16.0 O (1)(16.0) = g/mole 18.0 g/mole