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

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 Fire ball Sphere Uniform density

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

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” Still uniform density Bulk of the atom is positive Negative electrons float around

Rutherford’s Gold Foil Experiment Hypothesis Alpha emitter (positvie charge) screen Gold foil 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.

Rutherford’s Gold Foil Experiment ResultsConclusion 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 Dense positive center Mostly empty or unoccupied space Electrons float around randomly in the empty space >Click Me<

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)

ParticleSymbolChargeMassLocation protonp amu nucleus neutronn0 nucleus electrone - 1 1/1836 mass of a proton shell nucleons Nuclear charge Mass number = # of protons + #of neutrons Atomic number =#of protons X A Z Protons And neutrons # of Protons

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

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

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

Atomic 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 x 35 = x 37 = amu -is the weighted average of all naturally occurring isotopes. -based on the percent abundance and mass

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 the distribution of the electrons in an atom 2(n 2 ) Energy level st level 2nd level 3rd level Energy level Max # of e’s 1 2(1 2 )2 2 2(2 2 )8 3 2(3 2 )18 4 2(4 2 )32 5 2(5 2 )50 6 2(6 2 )72 7 2(7 2 )98 In theory We will assume only 32 per level

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 Ground state all electrons are in the lowest possible level will follow the pattern: Pattern on periodic table Excited state when an electron absorbs energy and jumps to a higher level can’t stay there pattern skips NOT on periodic table WAS: 2-8 (moved 1 e- to the next level) Atoms 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. represents atom from the nucleus to the valance shell are electrons in the outer energy level of the atom

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

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