Download The Structure of an Atom

The Structure of an Atom
Chapter 3
Early Theories
• Greek Philosophers
– 4 Elements
•
•
•
•
Air
Fire
Wind
Water
– Democritus
• Atoms make up matter
– Aristotle
• Refuted Democritus and
atom’s existence
forgotten
Deomcritus
Atoms
Differences in atoms
Dalton’s Atomic Theory
• All matter is composed of extremely small
particles called atoms.
• All atoms of a given element are identical.
• Atoms cannot be created, divided into smaller
particles, or distroyed.
• Different atoms combine in simple whole number
ratios to form compounds.
• In a chemical reaction, atoms are separated,
combined or rearranged.
Dalton’s Atomic Theory
• All matter is composed of extremely small
particles called atoms.
• All atoms of a given element are identical.
• Atoms cannot be created, divided into smaller
particles, or destroyed. (This part proven wrong)
• Different atoms combine in simple whole number
ratios to form compounds.
• In a chemical reaction, atoms are separated,
combined or rearranged.
Deomcritus
Atoms
Differences in atoms
Dalton
•Atoms
•Sameness
•Created/destroyed
•Combination
•Rearragement
Subatomic Particles and the Atom
• Cathode ray tube
– Stream of charged
particles (electrons).
– See pg 60 for picture
• J. J. Thompson
– Used cathode ray tube
to prove existence of
electron.
– Proposed “Plum
Pudding Model”
Subatomic Particles and the Atom
• Plum Pudding
• J. J. Thompson
• Plum Pudding Model
Deomcritus
Thompson
Atoms
•Atoms composed
of electrons
Differences in atoms
Dalton
•Atoms
•Sameness
•Created/destroyed
•Combination
•Rearragement
Ernest Rutherford
• Gold Foil experiment
– Used to prove the
existence of a
positively charged core
(Nucleus)
• The results were “like
firing a large artillery
shell at a sheet of
paper and having the
shell come back and
hit you!”
Ernest Rutherford
• What should have
happened
• What DID happened
Deomcritus
Thompson
Atoms
•Atoms composed
of electrons
Differences in atoms
Rutherford
Dalton
•Atoms
•Sameness
•Created/destroyed
•Combination
•Rearragement
•Positively Charged
Nucleus
Subatomic Particles and the Atom
• Chadwick
– Worked with Rutherford.
– Noted there was energy in the nucleus, but wasn’t the
protons.
– Concluded that neutral particles must aslo exist in
nucleus.
• Mosley
– Assigned atomic number to atoms
• Bohr
– Designed “Bohr Model” of the atom.
Deomcritus
Thompson
Atoms
•Atoms composed
of electrons
Differences in atoms
Rutherford
Dalton
•Atoms
•Positively Charged
Nucleus
•Sameness
Chadwick
•Created/destroyed
•Neutrons
exist in
Nucleus
•Combination
•Rearragement
Subatomic Particles and the Atom
• Three main particles: (see chart on pg 97)
– Proton
• Positive
• In nucleus
– Neutrons
• Neutral
• In nucleus
– Electrons
• Negative
• Orbiting the nucleus (not inside)
Atomic Differences
• Atomic Number
– Distinguishes one atom
from another.
– = #p+ (& #e- for a
neutral atom)
• Isotopes
– Differ in mass number
• Mass # = #p+ + #no
– Change is in # no
• Atomic Mass Unit
– Defined as 1/12 mass
of a Carbon-12 atom
• p+ = 1 amu
• no = 1 amu
• e- = 0 amu
Atomic Differences
• Mass on the periodic table is based on the
percent abundance of each isotope of that
element.
• Therefore it is a decimal.
• Ex: Chlorine exist naturally as Cl-37 and
Cl-35. Cl-37 is about 75% and Cl-35 is
about 25%. So, (37 X .75) + (35 X .25) =
36.5 amu.
• See Ex problem on pg 103 for more ideas.
Questions?
• Ask now, or forever come in the
morning for them!