Unit 1: Atoms

Scientists to Know …

DALTON

BOHR

CHADWICK THOMSON

RUTHERFORD

DEMOCRITUS

HEISENBERG

The History of Discovering the Atom

1. Philosophical Era

2. Alchemical Era

3. Classical Era

4. Subatomic Era

5. Modern Era– For later study…

1. Uncuttable Model

2. ---

3. The Dalton Sphere Model

4. The Plumb Pudding Model

The Planetary Model

5. The Quantum Model

The Timeline of Discovery The Intermediate Atomic Models

Brainstorm about this era?

THE PHILOSOPHICAL ERA (CIRCA 500~300BCE)

A time when logic ruled the land…

THE PHILOSOPHICAL ERA (CIRCA 500~300BCE)

Philosophical Era (Ancient Greece)

o Their ideas were based on logic, without experimental support (as was common in that time)

o Age of Thinking

Democritus (460-370 BCE)

o Argued that matter was made of small, indivisible particles

o Called the small particles “atomos” meaning “that which cannot be divided”

o Believed properties of matter came from the properties of

the “atomos”

Philosophical Era

Brainstorm about this era?

ALCHEMICAL ERA (300 BCE ~ 1400CE)

The “Dark Ages” of Chemistry where early chemists had to work in secret and encode their findings for fear of persecution

ALCHEMICAL ERA (300 BCE ~ 1400CE)

Alchemy

o the closest thing to the study of chemistry for nearly two thousand years

o Very mystical study and experimentation with the elements and what was perceived as magic

o Study was illegal, findings hidden in code

Alchemical Era

Elements in Alchemy

o Alchemists studied many different materials, and their properties, in order to find a way to turn lead into gold and achieve immortality

Alchemical Era

Brainstorm about this era?

THE CLASSICAL ERA (1400CE – 1887CE)

The printing press brings the widespread transfer and acquisition of knowledge

THE CLASSICAL ERA (1400CE – 1887CE)

John Dalton [really famous] (1766-1844)

o Dalton returns to Democritus’ ideas in 1803 with four argumentsI. All matter is made up of tiny particles called

atoms

II. All atoms of a given element are identical to one another and different from atoms of other elements

III. Atoms of two or more different elements combine to form compounds.

IV. A chemical reaction involves the rearrangement, separation, or combination of atoms. Atoms are never created nor destroyed during a chemical reaction.

Classical Era

John Dalton

The Atom

Brainstorm about this era?

THE SUBATOMIC ERA (1897CE – 1932CE)

The relatively quick discovery of things smaller than the once “indivisible” atom - EXPERIMENTAION

THE SUBATOMIC ERA (1897CE – 1932CE)

JJ Thomson o Use the cathode ray

tube (glass chamber used to study electricity in gasses) to discover the electron.

Subatomic Era

J.J. Thompson English (1897)

o Put magnetic fields near cathode rays (CRT)o Using three different arrangements of CRTs he was

able to determine that the Cathode rays…oWere streams of negatively charged particleso Those particles had very low mass-to-charge ratios

Subatomic Era

The First Subatomic Particleo Electrons – one part of an atom with one

negative chargeo Since atoms were known to be electrically

neutral, Thompson developed the plumb pudding model of the atom

Subatomic Era

Negatively (-) Charged electrons

Positively (+) charged majority

Ernest Rutherford New Zealander (1910)

o Rutherford worked with radiation and had heard of Thompson’s plumb pudding modelo He wanted to use radiation to prove Thompson’s model

o With the help from Marie Curie, he shot alpha particles (+) at an ultra-thin piece of gold foil, with a Geiger counter on the other side

Subatomic Era

Ernest RutherfordNew Zealand

Marie CuriePolish/ French

Rutherford’s Resultso Rutherford’s results were not what he expected

o Expected to have all alpha particles (+ charge) go straight through all of the atoms

o Saw that occasionally an alpha particle would ricochet

o Determined the positive charge of an atom must be held in a massive, centrally located, “nucleus”

Subatomic Era

The Second Subatomic Particle

o After more experiments the second subatomic particle was formally named (1911)o Proton

o Proton: The massive subatomic particle, within the nucleus of an atom, with a single positive charge

Subatomic Era

The Planetary Model (1911)

o Earnest Rutherford took his idea of a nucleus, and the known electrons, to construct a new atomic modelo Compact nucleus

oWith a positive center

o The orbit of the electrons kept them from falling directly into the nucleus, just like planetary motion

Subatomic Era

The Rutherford Model

orThe Planetary

Model

The Third Subatomic Particle

o Missing mass in the nucleuso James Chadwick – determined that a

another subatomic particle must be in the nucleus with the protons

o Called this subatomic particle: neutron because it has NO charge.

Subatomic Era

James ChadwickEnglish

Brainstorm about this era?

THE MODERN ERA (1900CE – PRESENT)

The Quark Era starts in 1964, but that advance can be regarded as outside the realm of chemistry – instead a part of nuclear physics

THE MODERN ERA (1900CE – PRESENT)

Bohr’s Planetary Model of the Atom

o integrated all known information into a new, math based, model of the atomoHe kept electrons in energy

levels or fixed orbits around the nucleus

Modern Era

Niels BohrDanish Physicist

The Modern (current) Atom

– Uncertainty Principle An electrons position,

momentum, energy and time can never be known at the same time.

Electrons are so small and relatively massless to measure it becomes impossible because any measuring technique causes it to change position / move.

Werner HeisenbergGermany

Modern Era

What does it look like?

• Likely electron locations are now represented as clouds or orbitals (bubbles)Electron Clouds

Electron

Bubbles

Modern Era