Timeline of Atomic Theory  Make sure it has Dates (some may not have dates) Important Peoples Names What they found/discovered/believed to be true The experiment they did Picture of the model they developed (if there is one)

The Atom What is it made of???

Protons  Positively charged  Mass = 1 amu = 1.67 x grams  Located in the nucleus  Gives an atoms its identity (atomic number)

Neutrons  Neutral charge  Mass = 1 amu =1.67 x grams  Located in the nucleus  Different numbers of neutrons define isotopes

Electrons  Negative charge  Mass = 1/1840 amu = 9.11 x grams  Located outside the nucleus (energy levels, shells, orbitals)  Equal to the number of protons in a neutral atom  Loss or gain of electrons gives ions their charge

Isotopes  The identity of the element depends on the number of protons  Atoms of the same element can have different number of neutrons.  Atoms of the same element that has different number of neutrons have different masses.

Isotope Designation Mass number Atomic number Element Symbol *Nuclides of Hydrogen

More Isotope Designation They both have 6 protons. Carbon-12 Carbon-14 6 neutrons 8 neutrons 6 neutrons 8 neutrons Plutonium-241 (Name of element- mass number) # neutrons = Mass # - atomic # # neutrons = Mass # - atomic #

Atomic Number  Gives an atom its identity  # Protons  The whole number in bold type in each element square (1) Cl Chlorine

Atomic Mass  The mass average of all naturally occurring isotopes of an element  The number expressed as a decimal in each element square Na Sodium

Determination of Atomic Mass  There are three isotopes of oxygen; and their relative abundances: Oxygen % Oxygen % Oxygen % Lets figure out the atomic weight of oxygen together!

Mass Number  Sum of the protons + neutrons  Always a whole number

Representation C 12 6 M A X Mass Number Atomic Number Symbol

Electron Energy Levels  1 has a maximum of 2 electrons Both in the “s” sublevel  2 has a maximum of 8 electrons 2 in the “s” sublevel 6 in the “p” sublevel  3 has a maximum of 18 electrons 2 in the “s” sublevel 6 in the “p” sublevel 10 in the “d” sublevel

Electron Energy Levels (cont.)  4 has a maximum of 32 electrons 2 in the “s” sublevel 6 in the “p” sublevel 10 in the “d” sublevel 14 in the “f” sublevel

Electron Configurations  Hydrogen – has only one electron in the first energy level and the first sublevel 1 H: 1s 1  Helium – has 2 electrons in the first energy level filling it to capacity 2 He: 1s 2

Electron Configurations (cont.)  Lithium – has 2 electrons in the first energy level and one in the second 3 Li: 1s 2 2s 1  Be – has 2 e - in the first energy level and 2 in the second but they both go into the “s” sublevel 4 Be: 1s 2 2s 2

Electron Configurations (cont.)  Carbon – has 2 electrons in the first energy level and four in the second 6 C : 1s 2 2s 2 2p 2  Fluorine – has 2 e - in the first energy level and 5 in the second but they go into both the “s” & “p” sublevels 9 F: 1s 2 2s 2 2p 5

Rules for Orbital Diagrams for an Atom  Aufbau – electrons fill lowest energy levels first ( follow the diagonal rule)  Pauli Exclusion Principle- There can only be 2 electrons in an orbital  Hund’s Rule – electrons fill equal energy orbitals with one first before they pair

Orbital Diagram for A Nitrogen Atom N 1s 2s 2p 3s  

Orbital Diagram for A Fluorine Atom F 1s 2s 2p 3s  

Orbital Diagram for A Magnesium Atom Mg 1s 2s 2p 3s 