ATOM Rich -Paradis Early Thoughts Aristotle-- Continuous theory Matter can be divided indefinitely Greeks matter is made up of particles--4 elements 4 elements --air--fire--water--- earth Democritus --Discontinuous theory Matter can not be divided indefinitely Atoms-indivisible Rich -Paradis

Dalton’s Atomic Theory ATOMIC THEORIES Dalton’s Atomic Theory • All elements are composed of individual atoms. •All atoms of a given element are identical • Atoms of different elements are different. •Compounds are formed by the combination of atoms of different elements (Law of Definite Proportions) Reactions are rearrangements of atoms Sphere Uniform density Fire ball

Cathode Tube -cathode rays are a form of radiation that contain an electrical charge -rays move from negative to positive -rays are negative (electrons) Cathode ray Negative electrode Positive electrode

JJ Thomson’s Model used the cathode ray tube to show one of the smaller units (particle) that make up the atom Thomson theorized that an atom contains small negatively charged particles -------electrons His model is the “Plum Pudding” Negative electrons float around Bulk of the atom is positive Still uniform density

Hypothesis Rutherford’s Gold Foil Experiment Alpha emitter (positvie charge) screen Gold foil Hypothesis Because the atom has uniform density, the alpha particles will pass straight through with little to no deflection. Like a bullet through a stick of butter.

Results Conclusion Rutherford’s Gold Foil Experiment The atom does not have uniform density. *Because the alpha particles passed through, there must be empty space. *Because the alpha particles were bounced back, they must have hit something dense. *Because the alpha particles were deflected, the dense part must have a positive charge.

Rutherford’s model Mostly empty or unoccupied space Dense positive center Electrons float around randomly in the empty space

Chadwicks -discovered the neutron -when doing studies, he found that the atom often weighed twice as much as he anticipated with the number of protons -he determined that there must be some other particle with the same mass as a proton but had no charge -neutrons are located in the dense positive center (nucleus)

X Particle Symbol Charge Mass Location proton p + 1 nucleus neutron n Subatomic Particle Symbol Charge Mass Location proton p + 1 1 amu nucleus neutron n electron e - 1 1/1836 mass of a proton shell nucleons Protons And neutrons Nuclear charge # of Protons X A Z Mass number = # of protons + #of neutrons Atomic number =#of protons

K I-131 Se I Calculate the number of protons, neutrons, and electrons. 39 19 I-131 Se 79 34 Mass # Rewrite: I 131 53 P- N- E- 34 P- N- E- 19 45 20 P- N- E- 53 34 19 78 When an atom is neutral (no charge), the number of electrons will equal the protons. 53

-has a charge (pos or neg) Ion -has a charge (pos or neg) Gain electrons = negative ion 17Cl - 35 P- 17 N- 18 E- 18 Lose electrons = positive ion 20Ca2+ 40 P- 20 N- 20 E- 18

Isotope C 14 6 -Atoms with the same atomic number, but different mass number -same bottom, different top -differ in the number of neutrons C 12 6

Atomic Mass -is the weighted average of all naturally occurring isotopes. -based on the percent abundance and mass 1. Write percent as decimal. 2. Multiply decimal by the mass #. 3. Add them up. 4. Units will be atomic mass units (amu) 75% Cl-35 25% Cl-37 .75 x 35 = 26.25 .25 x 37 = 9.25 35.50 amu

2(n2) 2-8-8 1st level 3rd level 2nd level 1 2(12) 2 2 2(22) 8 •proposed a model of the atom showing a dense nucleus with electrons found in surrounding orbits. •Bohr model shown shows a nucleus surrounded by electrons in circular orbits. •Each electron must posses just the right amount of energy to keep it in place around the nucleus. energy levels principal energy levels shells 2(n2) Energy level Energy level Max # of e’s 1 2(12) 2 2 2(22) 8 the distribution of the electrons in an atom 3 2(32) 18 2-8-8 4 2(42) 32 1st level 3rd level In theory We will assume only 32 per level 2nd level 5 2(52) 50 6 2(62) 72 7 2(72) 98

represents atom from the nucleus to the valance shell are electrons in the outer energy level of the atom quantum-- a discrete amount of energy -- each energy level represents a specific quanta -- to move from one level to another, you must use that much energy Excited state when an electron absorbs energy and jumps to a higher level can’t stay there pattern skips 2-7-1 NOT on periodic table WAS: 2-8 (moved 1 e- to the next level) Ground state all electrons are in the lowest possible level will follow the pattern: 2-8-18 Pattern on periodic table Electrons can not stay excited, when electrons drop to a lower level, energy is released in the form of light(photon). Each element gives off a specific color and spectrum.

R O Y G B I V •each element gives off their own bright continuous spectrum bright line spectra R O Y G B I V •each element gives off their own bright line spectrum •each line represents an electron dropping to a lower level •fingerprint of an element •white light through a prism or a diffraction gradient •shows all the colors in the visible spectrum •diffraction gradient separates the light

Modern Theory -- Wave (Quantum) Mechanical Model electron cloud electrons don’t travel in fixed paths but are located in regions of space called orbitals we don’t know the exact location of the electron but can guess where it is most likely located based on probability