1. Chemistry – King William High School

2.  Foundations…  Law of conservation of mass – mass is neither created nor destroyed  Law of definite proportions – a compound contains the same elements in the same proportions regardless of sample size  Law of multiple proportions – elements can form compounds in different ratios

3.  All matter is composed of atoms  Atoms of the same element are identical  Atoms cannot be subdivided, created or destroyed  Atoms of different elements combine in small whole number ratios to form compounds  In a reaction…atoms are combined, separated or rearranged (NOT destroyed!)

4.  What do we still take from Dalton…  All matter is composed of atoms  Atoms of one element differ in properties from atoms of another element

5.  Discovery of the electron  JJ Thompson  Plum Pudding model (electron’s = plums and protons = pudding)  Mass and charge of the electron  Millikan  Discovery of atomic nucleus  Rutherford  Gold foil experiment (nucleus has a dense, positive center)

6.  Nucleus = protons and neutrons (both with large mass)  Electrons outside the nucleus (very small mass…but large volume)

7.  Atomic number = the # of protons in the nucleus (and the # of electrons in a neutral atom)  Mass number = protons + neutrons  EX:

8.  Same element with different number of neutrons  Do not differ significantly in their chemical behavior  EX:

9.  Weighted average of the atomic masses of the naturally occurring isotopes of an element  The decimal # on the periodic table  EX: 10 5 B has an abundance of 19.91% and 11 5 B has an abundance of 80.09%. What is the atomic mass of boron?

10.  Avogadro’s number = 6.02 x 10 23  EX: How many moles of gold are in 5.64 x 10 36 atoms of gold?  EX: How many atoms of gold are in a sample that contains 0.259 mol?

11.  The mass of one mole of a pure substance  EX: What is the molar mass of potassium?  EX: What is the molar mass of water?

12.  EX: What is the mass in grams of 6.21 x 10 -2 mol of sodium?  EX: How many moles of copper are present in a 0.125 g sample?