Chemistry Unit 3- Historical Development of The Atom

Review over elements, important people, developments, nuclear radiation, and radioactive decay

In a normal (ordinary) reaction, matter cannot be created or destroyed, only rearranged

The Law of Conservation of Matter (Mass)

Stated all matter was made of ultimate (indivisible) particles called atoms, meaning there was a stopping point

Democritus

Stated all matter was continuous with NO stopping point (because you can keep breaking objects forever)

Aristotle

1st experimenters who experimented in secret, discovered medicines, gunpowder, etc.

Alchemists

Atomist known for advancements in astronomy

Galileo

Atomist known for working with gases

Boyle

Atomist known for working with TNT

Bacon

Atomist known for developing the laws of gravity & working with light refraction

Newton

The first people since Democritus to believe that matter was made of atoms

Atomists

The Father of modern chemistry, developed the Law of Conservation of Matter

Lavoisier

Studied iron pyrite (fool’s gold) and developed the Law of Definite Proportions

Proust

Came up with the first Atomic Theory & first model of the atom

1- All matter is made of indivisible particles (atoms)

2- Atoms of the same element are the same

3- Atoms of different elements are different

4- In a chemical reaction, atoms are only rearranged

5- Atoms of different elements combine chemically in definite proportions to make compounds

Dalton

Established modern system of chemical symbols for elements

J.J. Berzelius

Thought the atom was a tiny, indivisible, spherical particle. First model of the atom.

Dalton

Discovered canal rays, leading to the development of mass spectrometry

Goldstein

Discovered radioactivity (Curies were his grad students)

Becquerel

Discovered the electron by studying cathode ray tubes. Came to the conclusion that:

1- electrons are negative particles

2- electrons from all atoms are the same

3- electrons had an e/m ratio of 1.759 × 10^8 c/g

Developed the Plum Pudding Atom model (sphere of positive matter with electrons embedded throughout)

J.J. Thomson

Discovered the proton, finding out that:

1- Proton was charged +1

2- All protons had the same mass (1 amu)

*Idea of a proton shifted from being charged mass to being a charged particle

Wien

Known for the oil drop experiment (used to discover the charge and mass of the electron which was 1/12 of the mass of C-12)

Milikan

Discovered isotopes- using the Crookes’ Tube which separated particles by mass

J.J. Thomson

Known for the gold foil experiment & nuclear atom model.

Results:

-Most particles went straight through

-1/8000 particles went straight back

Conclusion:

-The atom is mainly empty space

-The atoms contain a tiny, dense, core called the nucleus

Rutherford

Developed the planetary atom- a tiny, dense nucleus with electrons that orbit in energy levels.

1. electrons in an atom can only exist if they have certain “allowed energies” (energy is quantized)

2. electrons orbit the nucleus at a calculated distance, determined by the electron energy.

Bohr

Developed the Quantum Mechanical Model and concept of the electron cloud

-realized electrons do not follow nice, neat paths

Schrodinger

Discovered the neutron- which acts as a spacer so that protons don’t repel

Chadwick

A set of mathematically defined regions in space around the nucleus

Electron cloud

Mass #

_______ ELEMENT SYMBOL

Atomic #

Nuclear Notation

A weighted average used for naturally occurring isotopes of an element

Atomic Mass

H

hydrogen

Li

lithium

Na

sodium

K

potassium

Rb

rubidium

Cs

cesium

Fr

francium

Be

beryllium

Mg

magnesium

Ca

calcium

Sr

strontium

Ba

barium

Ra

radium

B

boron

Al

aluminum

Ga

gallium

C

carbon

Si

silicon

Ge

germanium

Sn

tin

Pb

lead

N

nitrogen

P

phosphorus

As

arsenic

Sb

antimony

Bi

bismuth

O

oxygen

S

sulfur

Se

selenium

Te

tellurium

Po

polonium

F

fluorine

Cl

chlorine

Br

bromine

I

iodine

At

astatine