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ATOMIC THEORYATOMIC THEORY
Building blocks of matterBuilding blocks of matter
In the beginningIn the beginning
Empedocles: Earth, Fire, Water, AirEmpedocles: Earth, Fire, Water, Air
DEMOCRITUSDEMOCRITUS
IN 400 BC,DEMOCRITUS SAID:IN 400 BC,DEMOCRITUS SAID:
ALL MATTER IS MADE UP OF TINY PARTICLES ALL MATTER IS MADE UP OF TINY PARTICLES CALLED “ATOMOS” & empty spaceCALLED “ATOMOS” & empty spaceAtoms are solid, homogeneous, indestructible and Atoms are solid, homogeneous, indestructible and indivisibleindivisibleDifferent kinds of atoms have different shapes and Different kinds of atoms have different shapes and sizessizesDifferent props. of matter due to size, shape and Different props. of matter due to size, shape and movement of atomsmovement of atomsApparent changes in matter is result of changes of Apparent changes in matter is result of changes of atom groupingsatom groupings
AristotleAristotle
One of the most influential philosophersOne of the most influential philosophers
Disagreed with DemocritusDisagreed with Democritus
Didn’t believe in “nothingness” of empty Didn’t believe in “nothingness” of empty spacespace
Set science back almost 2000 Set science back almost 2000
yrs.yrs.
Antoine LavoisierAntoine Lavoisier
1743-1794; French chemist1743-1794; French chemist
Father of Modern ChemistryFather of Modern Chemistry
Conservation of MassConservation of Mass
He established the consistent use of chemical He established the consistent use of chemical balancebalance
developed a new system of chemical developed a new system of chemical nomenclature.nomenclature.
He was beheaded during the French revolution. He was beheaded during the French revolution.
Joseph ProustJoseph Proust
1754 -1826; French chemist1754 -1826; French chemist
Law of definite proportionsLaw of definite proportions
Compound always combines in the same Compound always combines in the same whole-number ratio regardless of the size whole-number ratio regardless of the size or source of the sampleor source of the sample
John DaltonJohn Dalton
Teacher at age 12Teacher at age 12
Loved meteorologyLoved meteorology
Law of Multiple ProportionsLaw of Multiple Proportions
Atoms of different elements combine in Atoms of different elements combine in different ratios to form different different ratios to form different compoundscompounds
Ex: CO vs COEx: CO vs CO22
Dalton pictured compounds as Dalton pictured compounds as collections of atoms. Here NO, NOcollections of atoms. Here NO, NO22, ,
and Nand N22O are represented.O are represented.
John John Dalton Dalton (1766 – 1844) (1766 – 1844) was an was an English English scientist who scientist who made his made his living as a living as a teacher in teacher in Manchester.Manchester.
Dalton’s atomic theoryDalton’s atomic theory
1808 JOHN DALTON / ATOMIC THEORY1808 JOHN DALTON / ATOMIC THEORY
1. All matter is made up of atoms1. All matter is made up of atoms
2. 2. Atoms of the same element are alike.Atoms of the same element are alike.
3. Atoms of different elements are different.3. Atoms of different elements are different.
4. Compounds have a definite composition 4. Compounds have a definite composition by weight and combine in small whole by weight and combine in small whole number ratios.number ratios.
5. 5. Atoms cannot be subdivided.Atoms cannot be subdivided.
Subatomic ParticlesSubatomic Particles
POSIT IVECHARG E
PROT ONS
NEUT RALCHARG E
NEUT RONS
NUCLEUS
NEG AT IVE CHARG E
ELECT RONS
AT OM
Most of the atom’s mass.
NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
ATOM
QUARKSAtomic Numberequals the # of...
equal in a neutral atom
Subatomic ParticlesSubatomic Particles
QuarksQuarks– component of component of
protons & protons & neutronsneutrons
– 6 types6 types
– 3 quarks = 3 quarks = 1 proton or 1 proton or 1 neutron1 neutron
He
PARTICLES OF THE ATOMPARTICLES OF THE ATOM
ELECTRON- JJ THOMPSON/1897ELECTRON- JJ THOMPSON/1897
– Mass/ MillikanMass/ Millikan
– PROTON AND NUCLEUS- RUTHERFORD/ 1911PROTON AND NUCLEUS- RUTHERFORD/ 1911
– ELECTRON SHELLS/ BOHR/ 1913ELECTRON SHELLS/ BOHR/ 1913
– NEUTRON-CHADWICK / 1932NEUTRON-CHADWICK / 1932
Are Atoms Really Are Atoms Really Unbreakable?Unbreakable?
J.J. Thomson investigated a beam called a J.J. Thomson investigated a beam called a cathode raycathode raydetermined that ray was made of tiny negatively determined that ray was made of tiny negatively charged particles -- charged particles -- electronselectronsmeasurements led him to conclude that these measurements led him to conclude that these electrons were smaller than a hydrogen atomelectrons were smaller than a hydrogen atomif electrons are smaller than atoms, they must be if electrons are smaller than atoms, they must be pieces of atomspieces of atomsif atoms have pieces, they must be breakableif atoms have pieces, they must be breakableThomson also found that atoms of different Thomson also found that atoms of different elements all produced these same electronselements all produced these same electrons
Schematic of a cathode ray Schematic of a cathode ray tube.tube.
Thomson’s Plum Pudding ModelThomson’s Plum Pudding Model Atom breakable!!Atom breakable!! Atom has structureAtom has structure Electrons suspended in a positively charged electric Electrons suspended in a positively charged electric
fieldfield– must have positive charge to balance negative must have positive charge to balance negative
charge of electrons and make the atom neutralcharge of electrons and make the atom neutral mass of atom due to electronsmass of atom due to electrons atom mostly “empty” spaceatom mostly “empty” space
– compared size of electron to size of atomcompared size of electron to size of atom
One of One of the early the early models of models of the the atom was atom was the plum the plum pudding pudding model.model.
Hantaro NagaokaHantaro Nagaoka
Japanese physicistJapanese physicistdeveloped the “Saturnian” system in 1904 developed the “Saturnian” system in 1904 resembled the planet Saturn, with rings of resembled the planet Saturn, with rings of electrons surrounding a concentrated, massive electrons surrounding a concentrated, massive positive charge positive charge inherently unstable. By radiating continuously, inherently unstable. By radiating continuously, the electron would gradually lose energy and the electron would gradually lose energy and spiral into the nucleus. spiral into the nucleus. No electron could thus remain in any particular No electron could thus remain in any particular orbit indefinitely.orbit indefinitely.
Robert MillikanRobert Millikan
Determined the charge of an electronDetermined the charge of an electron
E- transferred from brass atomizer to oil E- transferred from brass atomizer to oil droplets droplets
Droplets fell thru. vacuum chamberDroplets fell thru. vacuum chamber
Calculated the charge on the dropletCalculated the charge on the droplet
Multiple of one small chargeMultiple of one small charge
Rutherford’s Gold Foil ExperimentRutherford’s Gold Foil ExperimentHow can you prove something is empty?How can you prove something is empty?
put something through itput something through it– use large target atomsuse large target atoms
use very thin sheets of target so do not absorb “bullet”use very thin sheets of target so do not absorb “bullet”
– use very small particle as bullet with very high energy use very small particle as bullet with very high energy but not so small that electrons will affect itbut not so small that electrons will affect it
bullet = alpha particles, target atoms = gold foilbullet = alpha particles, target atoms = gold foil– particles have a mass of 4 amu & charge of +2 c.u.particles have a mass of 4 amu & charge of +2 c.u.– gold has a mass of 197 amu & is very malleablegold has a mass of 197 amu & is very malleable
Rutherford’s experiment on Rutherford’s experiment on -particle bombardment of metal -particle bombardment of metal
foil.foil.
Rutherford’s ResultsRutherford’s Results
Over 98% of the Over 98% of the particles went straight particles went straight throughthrough
About 2% of the About 2% of the particles went through but particles went through but were deflected by large angleswere deflected by large angles
About 0.01% of the About 0.01% of the particles bounced off the particles bounced off the gold foilgold foil
(a) The results that the metal foil (a) The results that the metal foil experiment would have yielded if the plum experiment would have yielded if the plum
pudding model had been correct. (b) pudding model had been correct. (b) Actual results.Actual results.
Rutherford’s Nuclear ModelRutherford’s Nuclear Model The atom contains a tiny dense center called the The atom contains a tiny dense center called the
nucleusnucleus– the volume is about 1/10 trillionth the volume of the volume is about 1/10 trillionth the volume of
the atomthe atom The nucleus is essentially the entire mass of the The nucleus is essentially the entire mass of the
atomatom The nucleus is positively charged The nucleus is positively charged
– the amount of positive charge of the nucleus the amount of positive charge of the nucleus balances the negative charge of the electronsbalances the negative charge of the electrons
The electrons move around in the empty space of The electrons move around in the empty space of the atom surrounding the nucleus the atom surrounding the nucleus
Ernest Ernest Rutherford Rutherford (1871 – 1937) (1871 – 1937) was born on was born on a farm in New a farm in New Zealand.Zealand.
Structure of the NucleusStructure of the NucleusThe nucleus was found to be composed of two The nucleus was found to be composed of two kinds of particleskinds of particles
Some of these particles are called Some of these particles are called protonsprotons– charge = +1charge = +1– mass is about the same as a hydrogen atommass is about the same as a hydrogen atom
Since protons and electrons have the same Since protons and electrons have the same amount of charge, for the atom to be neutral amount of charge, for the atom to be neutral there must be equal numbers of protons and there must be equal numbers of protons and electronselectrons
The other particle is called a The other particle is called a neutronneutron– has no chargehas no charge– has a mass slightly more than a protonhas a mass slightly more than a proton
Bohr ModelBohr Model
ee-- exist only in orbits with specific amounts exist only in orbits with specific amounts of energy called energy levelsof energy called energy levels
Therefore…Therefore…
– ee-- can only gain or lose certain amounts of can only gain or lose certain amounts of energy (energy (quantaquanta))
– only certain photons are producedonly certain photons are produced
The Modern AtomThe Modern Atom
We know atoms are composed of three main We know atoms are composed of three main pieces - protons, neutrons and electronspieces - protons, neutrons and electrons
The nucleus contains protons and neutronsThe nucleus contains protons and neutrons
The nucleus is only about 10The nucleus is only about 10-13-13 cm in diameter cm in diameter
The electrons move outside the nucleus with The electrons move outside the nucleus with an average distance of about 10an average distance of about 10-8-8 cm cm– therefore the radius of the atom is about 10therefore the radius of the atom is about 1055 times times
larger than the radius of the nucleuslarger than the radius of the nucleus
A A nuclear nuclear atom atom viewed viewed
in in cross cross sectionsection..
Atomic modelsAtomic modelsDalton
Thomson
Rutherford BohrH. Nagaoka