Transcript Chapter 3 Chemistry I notes

Early Models of the Atom
Democritus
Said that all things are made of tiny invisible particles called atomos
Joseph Louis Proust
Law of Constant Composition
A given compound always contains the same elements in the same
proportion by mass
John Dalton
• Atomic Theory of Matter
– Each element is made of small particles called
atoms
– All atoms of same element are identical.
– Atoms are neither created or destroyed
– A given compound has the same number and kind
of atoms
Atom
• Definition-
Discovering Atomic Structure
• Early scientists thought the atom was hard and round.
• Michael Faraday
– Said the structure of the atom was related to electricity.
• Static electricity
– Static means
– Electricity comes from the greek word Elekton
• Ben Franklin
– Kite Experiment
• Concluded that there are 2 charges
– Also concluded
J.J Thomson
• Cathode Ray Tube
– Simple version of the TV Tube
– Cathode had a
– Anode had a
– Concluded that the cathode ray was made of
negative particles
– He named the negative particles electrons
Robert Millikan
• Oil Drop Experiment
– Measured the charge of an electron
– Found the mass of the electron at 9.11 x 10-28 g
Radioactivity
• Henri Becquerel
– Accidently found radioactivity
– Placed uranium on photographic film
• Pierre and Marie Curie
– Isolated radium and polonium
– Given credit for discovering radioactivity
Ernest Rutherford
• Father of Chemistry
• Took over where JJ Thomson left off.
– Shot a beam of particles through two opposite charged
plates and called the positive particles alpha particle,
called the negative particles beta particles, and the neutral
substance was gamma waves.
• Gold foil experiment
– Look at class handout
– The reason the alpha particles split
-Named the nucleus
Models of the Atom
• Dalton’s model
– Round and hard sphere
• Thomson’s model ( Plum Pudding Model)
– Negative and positive charges evenly distributed
• Rutherford’s model
– Positive charges in the nucleus
– Negative charges out side the nucleus
• Bohr’s model
– Nucleus with protons and neutrons inside
– Electrons orbiting out side the nucleus
Bohr’s Model
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•
•
•
Protons = atomic number
Electrons= atomic number or protons
Neutrons= atomic mass – atomic number
Maximum number of electrons per orbit
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–
–
–
–
–
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1st orbit = 2
2nd orbit= 8
3rd orbit= 8
4th orbit = 18
5th orbit = 18
6th orbit = 32
7th orbit = 32
Henry Moseley
• Worked under Rutherford
• Found that the identity of the atom comes
from the number of positive charges
• He is given credit for naming the proton.
Ions
• Atoms that lose or gain electrons
• Positive ions lose electrons
• Negative ions gain electrons
– this is because of the charge of the electron
• Examples
Isotopes
• Atoms with the same number of protons but
different number of neutrons.
• Examples
Radioactive Decay
• Atoms emit one of three kinds of radiation
– Alpha equal to a helium atom
– Beta
equal to an electron
– Gamma no particles
• Alpha decay
– Ra 
– U 
+
+
• Beta decay
– I
– C


+
+
low penetration
mid penetration
high penetration