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