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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 x10-24 grams Located in the nucleus Gives an atoms its identity (atomic number) Neutrons Neutral charge Mass = 1 amu =1.67 x10-24 grams Located in the nucleus Different numbers of neutrons define isotopes Electrons Negative charge Mass = 1/1840 amu = 9.11 x10-28 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 235 92 U Element Symbol *Nuclides of Hydrogen 1 1 H 2 1 H 3 1 H More Isotope Designation Plutonium-241 (Name of element- mass number) # neutrons = Mass # - atomic # They both have 6 protons. Carbon-12 Carbon-14 6 neutrons 8 neutrons Atomic Number Gives an atom its identity # Protons The whole number in bold type in each element square (1) 17 35.453 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 11 22.990 Na Sodium Determination of Atomic Mass There are three isotopes of oxygen; and their relative abundances: Oxygen -16 Oxygen-17 Oxygen-18 99.759 % 0.037 % 0.204 % Lets figure out the atomic weight of oxygen together! Mass Number Sum of the protons + neutrons Always a whole number Representation Mass Number 12 C 6 Atomic Number M Symbol A X Electron Energy Levels 1 has a maximum of 2 electrons 2 has a maximum of 8 electrons Both in the “s” sublevel 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 22s1 Li: 1s 3 Be – has 2 e- in the first energy level and 2 in the second but they both go into the “s” sublevel 4 Be: 1s22s2 Electron Configurations (cont.) Carbon – has 2 electrons in the first energy level and four in the second C: 1s22s22p2 6 Fluorine – has 2 e- in the first energy level and 5 in the second but they go into both the “s” & “p” sublevels F: 1s22s22p5 9 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