Chapters Chapters

4, 5.1, + 254, 5.1, + 25

HISTORY OF THE ATOMIC HISTORY OF THE ATOMIC MODELMODEL

SCIENTIST MODELDemocritus: 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

SCIENTIST MODEL

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.

SCIENTISTSCIENTIST MODELMODEL

J.J. Thomson:J.J. Thomson: Thomson’s ModelThomson’s Model

(1856-1940)(1856-1940)

• 1897: Used cathode ray tube to discover electrons1897: Used cathode ray tube to discover electrons• Cathode ray:Cathode ray: glowing beam which travels from glowing beam which travels from

the cathode(-) to the anode(+).the cathode(-) to the anode(+).

- are composed of electrons- are composed of electrons

- are attracted to positive metal plate- are attracted to positive metal plate• Atoms had negatively charged particlesAtoms had negatively charged particles• ELECTRONELECTRON: : negatively charged subatomic particlenegatively 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 electronsa ball of positive charge containing electrons

Thomson’s ATOMIC ModelThomson’s ATOMIC Model

ELECTRONSEMBEDDED WITHIN

POSITIVE CHARGE

Cathode Ray Tube: Cathode Ray Tube:

http://www.chem.uiuc.edu/demos/cathode.htmlhttp://www.chem.uiuc.edu/demos/cathode.html

Robert Millikan (1868-1953) Robert Millikan (1868-1953) Oil Drop Experiment (1916)Oil Drop Experiment (1916)

Determined the Determined the charge and mass charge and mass of an electronof an electron

The mass is The mass is 1/1840 of the 1/1840 of the mass of a mass of a hydrogen atom hydrogen atom (unit)?(unit)?

SCIENTISTSCIENTIST MODELMODELErnest Rutherford:Ernest Rutherford: Rutherford’s ModelRutherford’s Model (1871-1937)(1871-1937)

• Gold Foil Experiment (1911)Gold Foil Experiment (1911)• Discovered that most of atom’s mass is located in the Discovered that most of atom’s mass is located in the

positively charged nucleuspositively charged nucleus

NUCLEUSNUCLEUS:: center of the atom composed of center of the atom composed of PROTONSPROTONS & & NEUTRONSNEUTRONS

is 99.9% of the atom’s massis 99.9% of the atom’s mass a marble in a football stadiuma marble in a football stadium

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swfhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

Empty Space

++++++ + Nucleus

Rutherford’s Gold Foil ExperimentRutherford’s Gold Foil Experiment: : (1911)(1911)

http://micro.magnet.fsu.edu/electromag/java/rutherford/ http://micro.magnet.fsu.edu/electromag/java/rutherford/

Gold Foil ExperimentGold Foil Experiment: Rutherford: Rutherford

PROTONPROTON: : positively charged subatomic particlepositively charged subatomic particle discovered by Eugen Goldstein (1850-1930)discovered by Eugen Goldstein (1850-1930) 1886: put holes in cathode and saw rays traveling 1886: put holes in cathode and saw rays traveling in the opposite direction (canal rays)in the opposite direction (canal rays)NEUTRONNEUTRON:: subatomic subatomic particle with no chargeparticle with no charge discovered by Sir James Chadwick discovered by Sir James Chadwick (1891-1974)(1891-1974) 1932: mass is nearly equal to proton (1 amu)1932: mass is nearly equal to proton (1 amu)

Thomson & Rutherford proved Thomson & Rutherford proved Dalton’s Theory incorrect: Dalton’s Theory incorrect: ATOMS ARE DIVISIBLEATOMS ARE DIVISIBLE

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swfhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

SCIENTISTSCIENTIST MODELMODEL

Niels Bohr: The Bohr Model (1885-1962)Niels Bohr: The Bohr Model (1885-1962)

Electrons move in definite orbits around Electrons move in definite orbits around the nucleus (planets around the sun)the nucleus (planets around the sun)

1913: PLANETARY MODEL1913: PLANETARY MODEL Electrons are a part of Electrons are a part of energy levelsenergy levels

located certain distances from the located certain distances from the nucleusnucleus

Electrons

++++++ Energy

Levels

Energy LevelsEnergy Levels: region around the nucleus where the: 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 a ladder that isn’t equally spaced further the distance, closer the spacingfurther the distance, closer the spacing the higher the energy level the farther it is from the the higher the energy level the farther it is from the

nucleusnucleus

Electrons can jump from 1 energy level to another.Electrons can jump from 1 energy level to another.

Quantum EnergyQuantum Energy: amount required to move an : 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.

SCIENTISTSCIENTIST MODELMODEL

Erwin Schrodinger Erwin Schrodinger Quantum Mechanic Model (1887-1961)Quantum Mechanic Model (1887-1961)

• 1926: Wave mechanics-mathematical1926: Wave mechanics-mathematical• Probable location of electronProbable location of electron• Cloud ShapedCloud Shaped• Propeller bladePropeller blade

Subatomic particles: Electrons, Protons, & NeutronsSubatomic particles: Electrons, Protons, & Neutrons Atomic NumberAtomic Number: Number of Protons in the nucleus: Number of Protons in the nucleus Whole number written above chemical symbolWhole number written above chemical symbol ExEx: : Hydrogen=1(P)Hydrogen=1(P) Oxygen=8(P)Oxygen=8(P)

Subatomic particlesSubatomic particles: : Electrons, Protons, & NeutronsElectrons, Protons, & Neutrons

Atomic NumberAtomic Number: Number of Protons in the : Number of Protons in the nucleusnucleus

• Whole number written above chemical symbolWhole number written above chemical symbolExEx: : Hydrogen=1(P)Hydrogen=1(P) Oxygen=8(P)Oxygen=8(P)

Atomic Mass #Atomic Mass #: Sum of Protons : Sum of Protons ++ Neutrons NeutronsExEx: : Carbon Mass #12 = 6(P) + 6(N)Carbon Mass #12 = 6(P) + 6(N)

Oxygen Mass #16 = 8(P) + 8(N)Oxygen Mass #16 = 8(P) + 8(N)A.Mass # (#P A.Mass # (#P + + #N)#N) - - Atomic # (#P)Atomic # (#P) = = #Neutrons#Neutrons

LETS HAVE SOME PRACTICELETS HAVE SOME PRACTICE

6

CCarbon

12

Atomic Number (P)

Mass Number(P+N)

Element Symbol

Element Name

126

Mass Number(P+N)

Atomic Number(P)

C

WHAT GIVES AN ATOM ITS WHAT GIVES AN ATOM ITS IDENTITY?IDENTITY?

IsotopeIsotope: Same # of Protons, : Same # of Protons,

different # of Neutronsdifferent # of Neutrons• Different Mass NumberDifferent Mass Number• Same Atomic NumberSame Atomic Number• Chemically alikeChemically alike

ExEx: : Carbon-12 Mass #12 = 6(P) + 6(N)Carbon-12 Mass #12 = 6(P) + 6(N)

Carbon-13 Mass #13 = 6(P) + 7(N)Carbon-13 Mass #13 = 6(P) + 7(N)

Atomic Mass for isotopes of Carbon = 12.01 amuAtomic Mass for isotopes of Carbon = 12.01 amu

SO, WHAT GIVES AN ATOM ITS SO, WHAT GIVES AN ATOM ITS IDENTITY?IDENTITY?

# of protons gives the atom its identity# of protons gives the atom its identity

# of electrons determines the chemistry # of electrons determines the chemistry of the atomof the atom

# of neutrons only changes the mass of # of neutrons only changes the mass of the atomthe atom

DO NOWDO NOW

There are 3 isotopes for OxygenThere are 3 isotopes for OxygenO-16O-16O-17O-17O-18O-18

1.1. Write the shorthand chemical symbol for Write the shorthand chemical symbol for all three isotopesall three isotopes

CC12 6

O-16 O O-16 O

O-17 OO-17 O

O-18 OO-18 O

16 8

17 8

18 8

Average Atomic MassAverage Atomic Mass

80% tests ---5080% tests ---50

20% homework---10020% homework---100

What is your average?What is your average?

(50+100)/2=75, not the case, (50+100)/2=75, not the case,

tests are weighted moretests are weighted more

.80x50= 40 .20x100=20.80x50= 40 .20x100=20

60 is your grade60 is your grade

Average Atomic MassAverage Atomic Mass

Two isotopes of carbon areTwo isotopes of carbon areC-12 the abundance is 98.89%C-12 the abundance is 98.89%C-13 the abundance is 1.11%C-13 the abundance is 1.11%What is the average atomic massWhat is the average atomic mass(12+13)/2=12.5(12+13)/2=12.5C-12: (98.89%/100) x 12=11.87C-12: (98.89%/100) x 12=11.87C-13: (1.11%/100) x 13=0.14C-13: (1.11%/100) x 13=0.1411.87+0.14=12.01amu11.87+0.14=12.01amu

Average Atomic MassAverage Atomic Mass

Do questions #23 & #24 on page 117Do questions #23 & #24 on page 117

DO NOWDO NOWDetermine the # of protons, neutrons, & Determine the # of protons, neutrons, &

electrons for the 4 isotopes of zinc:electrons for the 4 isotopes of zinc:

ProtonsProtons NeutronsNeutrons ElectronsElectrons

ZnZn 3030 3434 3030

ZnZn 3030 3636 3030

ZnZn 3030 3737 3030

ZnZn 3030 4040 3030

6430

6630

6730

7030

ProtonsProtons NeutronsNeutrons ElectronsElectrons

ZnZn

ZnZn

ZnZn

ZnZn

DO NOWDO NOW

Element X has two natural isotopes with Element X has two natural isotopes with mass 10.012 amu and a relative mass 10.012 amu and a relative abundance of 19.91%. The isotope with abundance of 19.91%. The isotope with mass 11.009 amu has a relative mass 11.009 amu has a relative abundance of 80.09%.abundance of 80.09%.

1. Calculate the atomic mass of this element 1. Calculate the atomic mass of this element (show all work) and then name this (show all work) and then name this element.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

http://www.furryelephant.com/player.php?subject=physics&jumpTo=re/2Ms4

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)