History of the

Atomic Theory

Ancient Greeks (B.C.)

•Aristotle•Four Elements:

•Earth•Water•Air•Fire

Greek Atomists (460B.C.)

• Democritus : Matter was made up of particles in perpetual motion and had the following characteristics:• Invisible• Solid• Indivisible• Eternal • Surrounded by an empty space• Infinite number of Shapes

Greek Atomists

• Archimedes disagreed with Democritus

• Archimedes was very highly respected and so everyone believed what he said

• Democritus’ ideas were tossed

Alchemy

• During the dark ages, earlier information was lost.• During the middle ages, people began to reinvestigate

nature and the structure of matter

• The plan : TRANSMUTATIONChange plain metals into noble metals- Lead Gold- Alchemists developed the Observation Experimentation Measurement

Classification Method.

Boyle (1661)

• Matter was made up of simple substances called ELEMENTS• Elements were substances

that could not be further decomposed

• He had no PROOF : qualitative experiments (what’s in it) no quantitative experiments (how much)

Lavoisier (1780)

• Developed quantitative experiments needed to prove Boyle’s theory• He heated mercury in air.• The silver mercury turned to a red

product, which was HEAVIER

200g of Mercury (grey) plus 16g Oxygen yields 216 g of red product

200g Hg + 16g O2 216 g HgO

Lavoisier

• To explain the increase, he reversed the experiment and heated the red product and collected the gas released

• Found that the amount of oxygen produced was equal to the increase in mass of his first reaction

216 g of red product (heated) yields 200g of Mercury plus 16g of Oxygen

216 g HgO 200g Hg + 16g O2

Lavosier

• Demonstrated the Law of Conservation of Mass;• Matter is neither created nor destroyed

during a chemical reaction

• Lavoisier classified substances as elements;• A substance that cannot be broken down

into simpler substance(s) by chemical means.

Gases

New names (French)Old names (English

translation)

Lumière Light

Calorique

Heat Principle of heat Igneous fluid Fire Matter of fire and of heat

Oxygène

Dephlogisticated air Empyreal air Vital air Base of vital air

AzotePhlogisticated gas

MephitisBase of mephitis

HydrogèneInflammable air or gas

Base of inflammable air

Metals

New names (French)Old names (English

translation)

Antimoine Antimony

Argent Silver

Arsenic Arsenic

Bismuth Bismuth

Cobolt Cobalt

Cuivre Copper

Étain Tin

Fer Iron

Manganèse Manganese

Mercure Mercury

Molybdène Molybdena

Nickel Nickel

Or Gold

Platine Platina

Plomb Lead

Tungstène Tungsten

Zinc Zinc

Lavoisier's table of simple substances

Nonmetals

New names (French)Old names (English translation)

Soufre Sulphur

Phosphore Phosphorus

Carbone Pure charcoal

Radical muriatique Unknown

Radical fluorique Unknown

Radical boracique Unknown

Earths

New names (French)Old names (English translation)

Chaux Chalk, calcareous earth

MagnésieMagnesia, base of Epsom salt

Baryte Barote, or heavy earth

AlumineClay, earth of alum, base of alum

SiliceSiliceous earth, vitrifiable earth

Lavoisier's table of simple substances

Dalton (1808)• Major Contribution: First Atomic theory

based on experimental evidence.• Reintroduced the idea of the atom

based on scientific experiments. • Small particles called atoms

• Can’t be subdivided • Can’t be created or destroyed• Properties of 1 atom are identical• Properties of atoms of different elements

differ• Atoms combine in simple ways to form

compounds (in definite whole number ratios)

Thomson (1897)

• Discovered the electron• Proposed an initial model

(Thomson’s Pudding)• Sphere of positive

substances mixed with negative electrons

• AKA Raisin Pudding Model

Millikan (1911)

• Determined the charge of an electron

• Used an oil drop experiment

Rutherford (1912)• His students were doing experiments

with radiation• Shot alpha particles through a thin

sheet of gold foil• Thought that the spaces in the atoms

were mainly empty, BUT• Some particles were reflected• Lead to the discovery of the Nucleus• The positive charge (or majority of

the atom’s mass) was concentrated in a small point.

• Introduced Atomic Planetary Model

The Rutherford Experiment

Bohr (1914)• Orbits can’t be anywhere –

they’re quantified• Quantified – specific numbers (like

quarters)• Greater the distance from the

nucleus, the greater the energy of an electron

• Orbits became known as energy levels

• Every atom in its normal (non excited) state, the electrons occupy the lowest energy levels available.

• Last in what we know as classical physics

Updating Atomic Theory• Scientists have learned a great deal about the

structure of matter• Atoms have many parts and a complex

organization• The essential ideas of Dalton’s theory are still

useful:• Elements are made of atoms• Compounds do form by the joining of atoms in

fixed whole number ratios• Properties of atoms of 1 element are identical• Properties of atoms of different elements differ.

Updating Atomic Theory

• 3 Major Differences: 1. Atoms can be subdivided

- Made up of protons, neutrons & electrons2. Atoms can be changed from one element to

another, but only by nuclear reactions3. Atoms of the same element are not all exactly

alike – they are alike in characteristics that determine chemical properties of that element but atoms of the same element can and DO have different masses (Isotopes)

Time Line

• BC – Ancient Greeks had the idea of an atom

• 1808 - Dalton’s atomic theory• 1886 – Protons discovered• 1897 – Electrons discovered• 1911 – Rutherford’s Experiment• 1913 – Bohr Model of an atom• 1932 – Neutron discovered

Quantum Physics

• Subatomic Particles• Electron probability

• Different Shapes• Charge-Cloud Model

• Doesn’t show paths of the electrons, instead it shows the most probable location of an electron

- Schrödinger

A Review

• Over the last 200 years, (especially in the 1900s) that many modifications were made to our conception of the structure of matter.

• Through the creativity and new technologies utilized by scientists, modifications and improvements were made.

• Science, technology and the affect of society’s thinking changed how we think of nature.

• Atoms are not solid spheres, but a combination of even smaller parts, each having a unique structure and function.