Download Chapter 3: Atomic Theory

Notes Monday, Sept. 16th
A. The Elements
Chapter 3:
Atomic Theory
• All of the materials in the universe can be
chemically broken down into about 100
different elements.
Elements, Atoms,
Compounds & Ions
and
1. Element can have several
meanings
Element
Element
Element
Microscopic form
Single atom of that
element
• Each element has a name and a symbol.
– The symbol usually consists of the first one
or two letters of the element’s name.
• Examples:
Oxygen O
Krypton Kr
Macroscopic form
Sample of that
element large enough
to weigh on a balance
– Sometimes the symbol is taken from the
element’s original Latin or Greek name.
Generic form
When we say the human body contains the element
sodium or lithium, we do not mean that free
elemental sodium or lithium is present. Rather we
mean that atoms of these elements are present in
some form.
B. Compounds
• Compounds are made by combining
atoms of the elements just as words are
constructed from the letters in the
alphabet.
Words
2. Names and Symbols for the
Elements
• Examples:
Sodium Na
Lead
Pb
Bromine Br
natrium (L. sodium carbonate)
plumbum (L. liquid silver)
bromos (Gr. stench)
1. Formulas of Compounds
• A compound is represented by a chemical
formula in which the number and kind of
atoms present is shown by using the element
symbols and subscripts.
Example: the simple sugar, glucose
Compounds
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Notes Monday, Sept. 16th
450 B.C. (Democritus)
• Greek Philosopher
• Matter is made up of
tiny indivisible particles
- ATOM “indivisible”
1808 (Dalton)
Original Atomic Theory
• All elements are composed of atoms
• All atoms of the same element are the
same
• Atoms of different elements are not
alike
• Solid sphere
Modern Definition
• Smallest particle of an element
that retains all chemical and
physical properties of that
element
Original Atomic Theory - Dalton
• Atoms (matter) cannot be created nor
destroyed – Chemical Reactions change the
arrangement of atoms
• Law of Constant Composition: a compound
always contains the same proportions by mass
of the elements. A given compound always
has the same number & arrangement of
elements
• Law of Multiple Proportions: different
compounds can be made having different
combinations of the same elements
1897 (Thomson)
• Used a Cathode Ray tube –identified
the presence of a negatively charged
particle
• http://www.chem.uiuc.edu/clcwebsite/cathode.html (this site
has a demo - link)
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Notes Monday, Sept. 16th
Cathode Ray
Tube
Evidence of a negatively charged component
with negative character:
The beam (cathode ray) originated from the
end connected to the negative charge.
The influence of a magnet: the positive end of
the magnet attracted the beam AND the negative
end of the magnet repelled the beam.
1911 (Rutherford)
• “Rutherford’s Experiment”
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
• “Shot” Alpha particles – positively
charged (4 amu) at gold foil
• Prediction: Alpha particles would
pass straight through gold foil
• Observed: Alpha particles were
deflected at various angles
1911 (Rutherford) cont’d.
Model from Thomson’s work
•“Plum Pudding” Model (Atom is a sphere of
positive electricity in
which electrons are
embedded)
http://lecture.lite.msu.edu/~mmp/kap29/cd719.htm
1911 (Rutherford) cont’d.
• Conclusion: Nuclear Atom
• Alpha particles met a large mass that
was positively charged within the
atom
• “Nucleus” - 1/100 000 the diameter of
the atom (extremely small), massive,
positively charged
(Rutherford) cont’d.
• By 1919 Rutherford introduced the
idea that the nucleus contained a
particle called the proton
• Proton: Same magnitude of charge as
an electron but opposite in charge (+)
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Notes Monday, Sept. 16th
1913 (Bohr’s Model)
• “Planetary model” - electrons
orbit around the nucleus in a
specific path
Nucleus
1932 (Chadwick)
• Discovered neutron mass equal
to that of a proton but no
electrical charge
electrons
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