Timeline

2000 1000 300 AD

American Independence

(1776)

Issac Newton(1642 - 1727)

400 BC

Greeks (Democratus ~450 BC)

Discontinuous theory of matter

ALCHEMY

Greeks (Aristotle ~350 BC))

Continuous theory of matter

Democritus (400 B.C.)

• proposed that matter was composed of tiny indivisible particles called atomos

• not scientifically tested

• "Nothing exists but atoms and empty space; everything else is opinion."

Democritus (400 B.C.)

• rejected by Aristotle and others who believed that matter could be endlessly divided

The GreeksHistory of the Atom

• Not the history of atom, but the idea of the atom

• In 400 B.C the Greeks tried to understand matter (chemicals) and broke them down into earth, wind, fire, and air.

• Democritus and Leucippus Greek philosophers

Greek Model

• Greek philosopher• Idea of ‘democracy’• Idea of ‘atomos’

– Atomos = ‘indivisible’– ‘Atom’ is derived

• No experiments to support idea

• Continuous vs. discontinuous theory of matter

Democritus’s model of atom

No protons, electrons, or neutrons

Solid and INDESTRUCTABLE

Democritus

“To understand the very large,

we must understand the very small.”

Four Element Theory

• Plato was an atomist• Thought all matter was

composed of 4 elements:– Earth (cool, heavy)– Water (wet)– Fire (hot)– Air (light)– Ether (close to heaven)

‘MATTER’

FIRE

EARTHAIR

WATER

Hot

WetCold

Dry

Relation of the four elements and the four qualities

Blend these “elements” in different proportions to get all substances

AnaxagorasAnaxagoras (Greek, born 500 B.C.)–Suggested every substance had its own kind of “seedsseeds” that clustered together to make the substance, much as our atoms cluster to make molecules.

Some Early Ideas on Matter

EmpedoclesEmpedocles (Greek, born in Sicily, 490 B.C.)–Suggested there were only four basic seeds – earth, air, fire, and water– earth, air, fire, and water. The elementary substances (atoms to us) combined in various ways to make everything.

Democritus (Thracian, born 470 B.C.)–Actually proposed the word atomproposed the word atom (indivisible) because he believed that all matter consisted of such tiny units with voids between, an idea quite similar to our own beliefs. It was rejected by Aristotle and thus lost for 2000 years.

AristotleAristotle (Greek, born 384 B.C.)–Added the idea of “qualities” – heat, cold, dryness, moisture – as basic elements– heat, cold, dryness, moisture – as basic elements which combined as shown in the diagram (previous page).

Hot + dry made fire; hot + wet made air, and so on.

Who Was Right?

• Greek society was slave based• Beneath famous to work with hands• did not experiment• Greeks settled disagreements by argument• Aristotle was more famous• He won!• His ideas carried through middle ages.• Alchemists change lead to gold

California WEB

Alchemy (next 2000 years)

Alchemy (next 2000 years)

• “Cast to him the body of the King, and when he has devoured it…in a great fire…the King will be liberated”– antimony is alloyed with gold and heated in order to purify the

gold

• “…fierce gray wolf…subject to the sway of warlike Mars…”– antimony is found mixed with

iron

• “…offspring of the ancient Saturn…”– antimony is derived from lead

Alchemy

. . . . . . . . . . . .. . .

GOLD SILVER COPPER IRON SAND

Alchemical symbols for substances…

transmutation: changing one substance into another

In ordinary chemistry, we cannot transmute elements.

Early Ideas on Elements

Robert Boyle stated...– A substance was an

element unless it could be broken down to two or more simpler substances.

– Air therefore could not be an element because it could be broken down in to many pure substances.

Robert Boyle

Contributionsof alchemists:

Information about elementsInformation about elements - the elements mercury, sulfur, and antimony were discovered- properties of some elements

Develop lab apparatus / procedures / experimental techniquesDevelop lab apparatus / procedures / experimental techniques - alchemists learned how to prepare acids. - developed several alloys - new glassware

Foundations of Atomic Theory

Law of Definite Proportions

The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound.

Law of Multiple Proportions

If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first elements is always a ratio of small whole numbers.

Law of Conservation of Mass

Mass is neither destroyed nor created during ordinary chemical reactions.

Law of Definite ProportionsJoseph Louis Proust (1754 – 1826)

• Each compound has a specific ratio of elements

• It is a ratio by mass

• Water is always 8 grams of oxygen for every one gram of hydrogen

Law of Definite Proportions

103 g ofcopper carbonate

53 g ofcopper

40 g of oxygen 10 g of carbon

+ +

Whether synthesized in the laboratory or obtained from

various natural sources, copper carbonate always has

the same composition.

Analysis of this compound led Proust to formulate

the law of definite proportions.

Law of Multiple ProportionsJohn Dalton (1766 – 1844)

If two elements form more than one compound, the ratio of the second element that combines with 1 gram of the first element in each is a simple whole number.

e.g. H2O & H2O2

water hydrogen peroxide

Ratio of oxygen is 1:2 (an exact ratio)

John Dalton (1807)

British Schoolteacher

• based his theory on others’ experimental data

Billiard Ball Model

• atom is a uniform, solid sphere

Dalton model

Dalton’s Four Postulates

1. Elements are composed of small indivisible particles called atoms.

2. Atoms of the same element are identical. Atoms of different elements are different.

3. Atoms of different elements combine together in simple proportions to create a compound.

4. In a chemical reaction, atoms are rearranged, but not changed.

Conservation of Atoms

John Dalton2 H2 + O2 2 H2O

4 atoms hydrogen2 atoms oxygen

4 atoms hydrogen2 atoms oxygen

H

H

O

O

O

O

H

H

H

H

H

H

H2

H2

O2

H2O

H2O

+

Daltons Atomic Theory

• Dalton stated that elements consisted of tiny particles called atoms

• He also called the elements pure substances because all atoms of an element were identical and that in particular they had the same mass.

Dalton’s Theory Continued

• He also said the reason why elements differed from one another was that atoms of each element had different masses.

• He also said that compounds consisted of atoms of different elements combined together.

• Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behaviour that was determined by what kind of element they were.

Structure of Atoms

• Scientist began to wonder what an atom was like.

• Was it solid throughout with no internal structure or was it made up of smaller, subatomic particles?

• It was not until the late 1800’s that evidence became available that atoms were composed of smaller parts.

Dalton’s Symbols

John Dalton 1808

Daltons’ Models of Atoms

Carbon dioxide, CO2

Water, H2O

Methane, CH4

Dalton’s Atomic Theory1. All matter consists of tiny particles.

Dalton, like the Greeks, called these particles “atoms”.

2. Atoms of one element can neither be subdivided nor changed into atoms of any other element.

3. Atoms can neither be created nor destroyed.

4. All atoms of the same element are identical in mass, size, and other properties.

6. In compounds, atoms of different elements combine in simple, whole number ratios.

5. Atoms of one element differ in mass and other properties from atoms of other elements.

II. Periodic Table A. Introduction

1869 - Dmitri Mendeleev (Russian chemist) & Julius Lothar Meyer (German chemist) independently arranged the known atoms by atomic weight (now by atomic number).