Transcript PP PH Ch. 4.1-4.2 - Liberty Union High School District

Ch. 4 Atomic Structure
4.1 Defining the Atom
Early Models of the Atom
• Democritus’s Atomic Philosophy
– He believed atoms were indivisible and
idestructible.
– Philosophy because there is no experimental
support
– video
Dalton’s Atomic Theory
• John Dalton (1766-1844)
• Theory because he had experimental
support
Dalton’s vs. Modern Atomic Theory
1. Elements are composed
of tiny, indivisible atoms.
2. Atoms of same element
are identical
3. Different elements can
mix or react to make
compounds.
4. When chemical
reactions occur,
elements rearrange but
no new elements.
1. Elements are made of
atoms BUT atoms are
divisible.
2. Atoms are not absolutely
identical. Isotopes –
different mass but same
properties.
3. Same as Dalton’s
4. Same as Dalton’s
4.2 Structure of the Atom
Location of Particles
• Nucleus (positive charge)
– Protons and Neutrons
• Electron Cloud (negative charge)
– Electrons video
Discovery!! Electrons
• Electrons were discovered:
– by J.J. Thomson in 1897 (don’t memorize
date)
– Through experiments with a cathode ray tube
• Determined existence, negative charge and mass
• video
Protons and Neutrons
Discovered!
• Protons were discovered:
– By Eugene Goldstein in 1886
– Also through the use of cathode ray tubes
• Discovered positive charge
• Neutrons were discovered:
– By James Chadwick in 1932
– By bombarding boron with alpha particles
• Discovered no charge
Nucleus Discovered!!
• Atomic theories: Chocolate chip cookie
dough theory: Protons, neutrons were
dough and electrons choc. Chips spread
throughout.
• Rutherfords Gold Foil Experiment
– Bombarded gold foil with alpha particles and
found some of the particles rebounded.
– Must be small hard center in middle of atom
Gold foil experiment
• http://www.mhhe.com/physsci/chemistry/e
ssentialchemistry/flash/ruther14.swf
• Click on the above link.
Analogy
• Rutherford’s experiment v. firing a gun
Nucleus size
• Nucleus v. electron cloud
• Do you see the tiny star?