Chapters 4, 5.1, + 25 HISTORY OF THE ATOMIC MODEL

SCIENTISTMODEL Democritus: The Greek Model (460 BC – 370 BC) 400 BC: Matter can’t be divided forever; there must be a smallest piece (atomos) Atoms are indestructible, indivisible, & the fundamental units of matter Atom: smallest particle of an element that retains the properties of that element. - no electric charge, electrically neutral No experiments to test his theories

SCIENTISTMODEL John Dalton:Dalton’s Model (1766 – 1844) Dalton’s Atomic Theory (1803): All elements are composed of atoms that are submicroscopic indivisible particles. Atoms of the same elements are identical & atoms of different elements are different. Atoms of different elements can physically mix together or chemically combine w/one another to form simple whole- number ratios to form compounds. Chemical reactions occur when atoms are separated, rearranged or joined. Atoms of one element can never be changed into atoms of another element.

SCIENTISTMODEL J.J. Thomson: Thomson’s Model ( ) ( ) 1897: Used cathode ray tube to discover electrons 1897: Used cathode ray tube to discover electrons Cathode ray: glowing beam which travels from Cathode ray: glowing beam which travels from the cathode(-) to the anode(+). the cathode(-) to the anode(+). - are composed of electrons - are attracted to positive metal plate Atoms had negatively charged particles Atoms had negatively charged particles ELECTRON: negatively charged subatomic particle ELECTRON: negatively charged subatomic particle not the original name (corpuscle)not the original name (corpuscle) “Plum Pudding” Model “Plum Pudding” Model (chocolate chip cookie) (watermelon) (chocolate chip cookie) (watermelon) - a ball of positive charge containing electrons- a ball of positive charge containing electrons

Thomson’s ATOMIC Model ELECTRONS EMBEDDED WITHIN POSITIVE CHARGE

Cathode Ray Tube:

Robert Millikan ( ) Oil Drop Experiment (1916)  Determined the charge and mass of an electron  The mass is 1/1840 of the mass of a hydrogen atom (unit)?

SCIENTISTMODEL Ernest Rutherford:Rutherford’s Model ( ) ( ) Gold Foil Experiment (1911) Gold Foil Experiment (1911) Discovered that most of atom’s mass is located in the positively charged nucleus Discovered that most of atom’s mass is located in the positively charged nucleus NUCLEUS: center of the atom composed of PROTONS & NEUTRONS  is 99.9% of the atom’s mass  a marble in a football stadium Empty Space Nucleus

Rutherford’s Gold Foil Experiment : (1911)

Gold Foil Experiment: Rutherford

PROTON: positively charged subatomic particle discovered by Eugen Goldstein ( ) discovered by Eugen Goldstein ( )  1886: put holes in cathode and saw rays traveling in the opposite direction (canal rays) in the opposite direction (canal rays) NEUTRON: subatomic particle with no charge discovered by Sir James Chadwick discovered by Sir James Chadwick ( ) ( )  1932: mass is nearly equal to proton (1 amu) Thomson & Rutherford proved Dalton’s Theory incorrect: ATOMS ARE DIVISIBLE

SCIENTIST MODEL Niels Bohr: The Bohr Model ( )  Electrons move in definite orbits around the nucleus (planets around the sun)  1913: PLANETARY MODEL  Electrons are a part of energy levels located certain distances from the nucleus Electrons +++ Energy Levels

 Energy Levels: region around the nucleus where the electron is likely to be moving. electron is likely to be moving.  a ladder that isn’t equally spaced  further the distance, closer the spacing  the higher the energy level the farther it is from the nucleus Electrons can jump from 1 energy level to another. Electrons can jump from 1 energy level to another.  Quantum Energy: amount required to move an electron from its present energy electron from its present energy level to the next higher one. level to the next higher one.

SCIENTISTMODEL Erwin Schrodinger Quantum Mechanic Model ( ) 1926: Wave mechanics-mathematical 1926: Wave mechanics-mathematical Probable location of electron Probable location of electron Cloud Shaped Cloud Shaped Propeller blade Propeller blade Subatomic particles: Electrons, Protons, & Neutrons  Atomic Number: Number of Protons in the nucleus  Whole number written above chemical symbol  Ex: Hydrogen=1(P)Oxygen=8(P)

Subatomic particles: Electrons, Protons, & Neutrons  Atomic Number: Number of Protons in the nucleus Whole number written above chemical symbol Whole number written above chemical symbol Ex: Hydrogen=1(P)Oxygen=8(P)  Atomic Mass #: Sum of Protons + Neutrons Ex: Carbon Mass #12 = 6(P) + 6(N) Oxygen Mass #16 = 8(P) + 8(N) A.Mass # (#P + #N) - Atomic # (#P) = #Neutrons

LETS HAVE SOME PRACTICE 6 C Carbon 12 Atomic Number (P) Mass Number (P+N) Element Symbol Element Name 12 6 Mass Number (P+N) Atomic Number (P) C

WHAT GIVES AN ATOM ITS IDENTITY?  Isotope: Same # of Protons, different # of Neutrons Different Mass Number Different Mass Number Same Atomic Number Same Atomic Number Chemically alike Chemically alike Ex: Carbon-12 Mass #12 = 6(P) + 6(N) Carbon-13 Mass #13 = 6(P) + 7(N) Atomic Mass for isotopes of Carbon = amu

SO, WHAT GIVES AN ATOM ITS IDENTITY?  # of protons gives the atom its identity  # of electrons determines the chemistry of the atom  # of neutrons only changes the mass of the atom

DO NOW There are 3 isotopes for Oxygen O-16O-17O Write the shorthand chemical symbol for all three isotopes C 12 6

O-16 O O-17 O O-18 O

Average Atomic Mass 80% tests % homework What is your average? (50+100)/2=75, not the case, tests are weighted more.80x50= 40.20x100=20 60 is your grade

Average Atomic Mass Two isotopes of carbon are C-12 the abundance is 98.89% C-13 the abundance is 1.11% What is the average atomic mass (12+13)/2=12.5 C-12: (98.89%/100) x 12=11.87 C-13: (1.11%/100) x 13= =12.01amu

Average Atomic Mass  Do questions #23 & #24 on page 117

DO NOW Determine the # of protons, neutrons, & electrons for the 4 isotopes of zinc: ProtonsNeutronsElectrons Zn Zn Zn Zn ProtonsNeutronsElectronsZn Zn Zn Zn

DO NOW Element X has two natural isotopes with mass amu and a relative abundance of 19.91%. The isotope with mass amu has a relative abundance of 80.09%. 1. Calculate the atomic mass of this element (show all work) and then name this element.

Nuclear Chemistry   The study of changes in matter that originate in atomic nuclei   What makes a nucleus unstable? Too many or Too few neutrons relative to the # of protons   The nuclei of unstable isotopes gain stability by undergoing changes

Changes that Radioactive Isotopes Undergo   Alpha α particle Release of helium nuclei Rutherford’s Gold Foil Exp.   Beta β particle Release of an electron from the breaking apart of a neutron in an atom   Gamma γ ray Release of photons (light energy)

What can they penetrate?   Alpha α =almost nothing Inhalation (radon) Open wounds Can’t go through skin, paper, wood, plastic, lead, concrete   Beta β = somethings Skin & paper Can’t go through wood, plastic, lead, concrete   Gamma γ = a lot of stuff Skin, paper, & wood Can’t go through lead or concrete

Half-Life   Unstable isotopes have a rate of decay, known as half-life

Uses of Radioactive Isotopes   Carbon dating (pg. 806, 814,815)   Geiger counter (pg 817)   Film Badge (817)   Agriculture tracers (pg 818)   Treating Cancer (pg 819)