History of the atom (atomic theory)

Greeks:

Democritus (~400 BC); strictly philosophy

World made of two things:

Empty space and tiny particles

The word atom comes from the Greek word:

Atomos

To not cut (indivisible)

The smallest bit of matter that could be conceived

Contradicted Aristotle until Dalton

Alchemist

First to study matter using a laboratory

Main work was to try and change matter from one form to another

Transmutation

Pb → Au

Lead into Gold

John Dalton

Early 1800’s

Father of Atomic Theory

Used quantitative measurements

Explained how matter links together in definite proportions (worked with gases)

His proportions were based on MASS

Worked with water “molecules”

Ratios:

Mass- 8 O to 1 H

Atoms- 2 H to 1 O per molecule

Volume- 2 H to 1 O

2 H2O → 2 H2 ↑ + O2 ↑

Coined the terms:

Monatomic molecule (H)

Diatomic molecule (H2)

Chemical bonds

JJ Thompson

Late 1800’s

Discovered the electron and the proton

Subatomic particles

Atom made of negative particles mixed equally in a sphere of positive material

Plum pudding model

Ernest Rutherford

1912- 1919

Atoms have a small center

Occupies ~ 10-12 % of the atoms volume

The center has a positive charge (+); nucleus

Mass of the atom is concentrated in its nucleus

# of electrons MUST = # of protons

Electrically neutral

Evidence for protons in the nucleus movie

Nagaoka model

Electrons revolving around the nucleus like the planets around the sun

Neils Bohr

~ 1913

Used quantum mechanics

Electrons found in “shells” or energy levels

1st shell can hold 2 electrons

2nd shell can hold 8 electrons

Successive shells can hold more electrons

Maximum of 7 shells

Octet rule

http://jersey.uoregon.edu/vlab/elements/Elements.html

Schrodinger model (Wave model)~1929

Current model (Quarks; superstring theory ?)Abandoned the idea of precise orbits for electronsPauli exclusion principleHeisenberg uncertainty principle“spdf” model

Describes the regions of space where electrons are most likely to be found

Based on work by Louis de Broglie

Atoms are 99.9999999 % empty space

Protons and neutrons are held together in the nucleus by the strong force

The weak force accounts for radioactivity

Very important

Electrons orbit the nucleus at different energy levels

Within each energy level you can have orbitals

s orbital (1) can hold a max of 2 electrons

p orbital (3) can hold a max of 6 electrons

d orbital (5) can hold a max of 10 electrons

f orbital (7) can hold a max of 14 electrons

Electrons are found in orbitals within energy levels

s orbital p orbital

d orbital (x-y) d orbital (z)

Pauli exclusion principle

Only 2 electrons per orbital

# of electrons in the outer most energy level determines how the atom react with other atoms; ∴ the properties of that atom

These electrons have a name:

Valence electrons

Walter Bothe and Sir James Chadwick

1930- 1932

Discovered the neutron

Same mass as the proton BUT no charge

Atomic structure

A. Quarks

Hypothetical particles (smallest form of matter)

Proposed in 1963 (Gell- Mann and Zweig)Quarks have fractional chargesCome in six flavorsGrouped together in threes to form almost all subatomic particles

Experimental evidence exist to show ALL six flavors exist

Each quark has an antiquark; antimatter

Gluon is the force that holds quarks together

B. Subatomic particles (3 types)

1. Proton (+ charge; has mass)

2. Neutron (no charge; has mass)

3. Electron (- charge; has mass BUT very little)

1 and 2 found in the atomic nucleus AND

Accounts for ALL of the atom’s mass

Atomic Terms

A. Atomic Number

Total # of protons in the nucleus

Total # of electrons

Name of the atom (element)

# of protons = # of electrons

B. Atomic Mass Number

# of protons + # of neutrons in the nucleus of the atomIn the periodic table atomic mass number that we see is an average of all the different types of isotopes for that atom (this is why the atomic mass number is not even)

To find the # of neutrons in a atom:

# of neutrons = Atomic Mass # - Atomic #

C. Isotopes

The name, of the atom, remains the same.

Has the same number of protons and electrons.

Has a different number of neutrons.

Some isotopes are radioactive (Radioisotopes)

α β γ emitters

D. Ions

Same number of protons/ neutrons

Different number of electrons (add or remove)

Ions have a “net charge” (either + or -)

Not very stable

• One fact we know… is that atoms are very, very old.

• All the atoms, on the Earth, are older than the sun and Earth.

• All of the subatomic particles in your body have existed since the beginning of time.

The Ultimate Recycling

Atoms – How Old Are You???

Program

• Scottish botanist, Robert Brown- noticed that the grains of pollen under his microscope were continually moving while suspended in the water mount.

- now called “brownian motion”, the collision of visible particles and invisible atoms.

Atoms - Visual Evidence in 1827

• Hydrogen was the first element to form in the universe.

• Today, H2 accounts for 90% of all elements.

• All other elements are heavier than H2. These other elements were probably manufactured in stars that have exploded and have formed our solar system. Super nova

B. General Information