Evolution of Atomic Theory & Counting Atoms Cover Chapter 3 today Quiz on Isotope Lab (you don’t need to wear pants)=

Evolution of Atomic Theory Democritus: 1) Matter consists of very small, indivisible particles, called atoms.

Dalton’s Atomic Theory Elements are made from tiny particles called atoms. All atoms of a given element are identical. The atoms of a given element are different to those of any other element. Atoms of different elements combine to form compounds. A given compound always has the same relative numbers and types of atoms (Law of constant composition). Different compounds made up of the same elements differ in the # of atoms of each kind that combine. (Law of multiple proportions) 6. Atoms cannot be created or destroyed in a chemical rxn, they are simply rearranged (law of conservation of mass).

J. J Thomson Cathode Ray Experiment

Millikan Oil Drop Experiment

Rutherford Gold Foil Experiment

Subatomic Particles Protons: p+ 1) +1 charge, located in the nucleus 2) this is the atomic # - the atomic # = number of p+ 3) also known as Z 4) identifies the element (i.e. you can’t change the # of p+ without changing the ID of the element.

Subatomic Particles Neutrons: n0 1) neutral; located in the nucleus 2) A – Z , where A = the mass number of the element 3) Isotopes of the same element have a different # of neutrons.

Subatomic Particles Electrons: e- 1) -1 charge; located outside of nucleus in orbitals 2) For neutral atoms, # p+ = # e-

Mass # & Avg. Atomic Mass

Isotopes Atoms of the same element Have the same # of ___________, but different #’s of ___________. Isotopes have different masses, but the same atomic number aka, “nuclide”: general term for any isotope of any element that is identified by numbers of protons and neutrons. Hyphen Notation Isotope Notation X A Z 3 1 H Hydrogen- 3

Atomic Mass Units What unit is appropriate for finding the mass of a car? What unit is appropriate for finding the mass of a paper clip? What unit is appropriate for finding the mass of an atom?

Atomic Mass Units (cont.) Just like with all other units, there must be a standard against which to define the amu, that standard is the C-12 nuclide. C-12 has been assigned exactly 12 amus 1 amu is exactly 1/12 the mass of one C-12 or 1.6605 x 10-27kg

Atomic mass numbers that are not whole numbers? Example: 35.5Cl17 There are not 18.5 neutrons! Where is the .5 coming from? There are more than one isotope of chlorine that exists in nature,35Cl17 & 37Cl17 How do I figure out the average atomic mass when considering the isotopes present in a natural sample?

Average Atomic Mass Average = (% of each isotope • atomic mass of each isotope) Atomic Mass 100 Example: Boron has two isotopes 10B5 and 11B5. They have the abundance 18.7 % and 81.3 % respectively Average Atomic mass = ((10)(18.7)) + ((11)(81.3)) 100 = 10.8 amu Example 2: In a given sample of carbon there will be 98.90% of C-12, 1.10% of C-13, and a small trace of C-14, what is the average atomic mass?

Atoms vs. Ions Atoms are Neutral Ions are Charged atoms There are two kinds of ions Cations + charged ions # p+ > # e- Have lost e- Are metals X+ Anions - charged ions # p+ < # e- have gained e- Are non-metals X-

Mole Concept SI base unit: mole (mol) - amount of substance The # of molecules in a mole = avogadro’s # = 6.02 x 1023 Just as 1 dozen oranges contains 12 oranges, 1 mole of hydrogen contains 6.02 x 1023 H atoms.

Molar Mass This is the mass of 1 mole of units (atoms, molecules, formulas units, or particles) of a substance. We can say that 12.01g C = 1mol C ____g H = 1 mol H

Putting it all together 1 mol = 6.02 x 1023 atoms, particles, formula units, or molecules Molar mass = g/mol Average atomic mass = amu Example: How many moles of He atoms are in 6.46g of He? Example 2: How many atoms are in 16.3g of S?

6.02 x 10 23 atoms, molecules, formula units, or particles Some more examples Mass of Element (m) # of Moles of Element (n) # of atoms of Element (N) Molar Mass g/mol 6.02 x 10 23 atoms, molecules, formula units, or particles Calculate the # of atoms in 0.551 g of potassium. Calculate the # of grams of lead in 12.4 moles of lead. Calculate the # of grams of H2O in 6.5 moles of water.