Atomic Structure- History

Philosophers and Scientists• Know how the following contributed to the history of

the atom:Philosophers from History of the Atom video– Empedicles - four “elements” – earth, water, fire, air.

– Leucippus - the first Greek to develop the theory of atomism — the idea that everything is composed entirely of various imperishable, indivisible elements called atoms

– Aristotle - five elements – earth, air, fire, water, and aether

Next week

Modern Day scientists– Dalton• atoms could not be divided• all elements of a given element are the same• different atoms could join to form compounds

– Thomson• the plum pudding model• negatively-charged "plums” surrounded by

positively-charged "pudding”– Rutherford http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf

• atom is made up of a central charge surrounded by a cloud of orbiting electrons

– Bohr• electrons are in levels around the nucleus

Structure of the Atom

Particle Charge Mass

(atomic mass units)

Location

Proton positive

+

1 nucleus

Neutron neutral

Ø

1 nucleus

Electron negative

-

0.0006 orbit, level, cloud

The Nucleus

A 1946 test of an atomic bomb in the lagoon at Bikini atoll. The explosion has just started; surplus ships moored nearby can still be

seen.

http://video.google.com/videosearch?sourceid=navclient&rlz=1T4SUNA_enUS3

16US316&q=atomic%20bomb&um=1&hl=en&ie=UTF-

8&sa=N&tab=iv#

http://www.youtube.com/watch?v=bw85r24WW3s

• The nucleus– the center of the atom composed

of protons and neutrons– held together by four forces (electromagnetic,

strong , weak, and gravity)– 99.9% of the atom’s mass is here– about 100,000 times smaller than

the entire atom– the atomic number of an atom is the number

of protons in the nucleus– the atomic mass or mass number of an atom is

the sum of the protons and neutrons

– Isotopes• atoms with the same number of protons (and

therefore the same element) but with a different number of neutrons.