Download Atomic Structure

Atoms: The Building
Blocks of Matter
Dalton’s Atomic Theory (1803)
1. All matter is made of atoms.
2. Atoms of the same element are identical.
Atoms of different elements differ.
3. Atoms cannot be divided, created, nor
destroyed.
4. Atoms combine in simple whole number
ratios to form compounds.
5. Atoms are rearranged, separated, or
combined in chemical reactions.
Dalton’s model of atom (1803)
Solid, Indivisible
Sphere of Matter
J.J. Thomson & Cathode Ray (1897)
J.J. Thomson & Cathode Ray (1897)
• Rays repelled by negatively charged object.
• Charge to mass ratio same regardless of type of metal or
gas used in the tube
• Concluded that identical negative particles are in all
atoms. Named them electrons.
• Since atoms are neutral, they must also contain a
positive charge.
JJ
Thomson’s
Model
Millikan & Oil Drop Experiment (1909)
Millikan & Oil Drop Experiment (1909)
• Measured charge of electron
• Allowed mass of electron to be determined from
charge and charge to mass ratio.
• Mass of electron much smaller than mass of
atom, so the atom must contain other particles to
account for most of the mass.
Rutherford and Gold Foil Experiment (1911)
Result of experiment
Results and Conclusions
• Most alpha particles went through foil
while a few bounced back.
• Atom is mostly empty space with a dense,
concentrated positive mass in the center.
• Electrons occupy space around the
nucleus.
Modification of plum-pudding model
Prediction of what would
occur with plum-pudding model.
Explanation for why a few alpha
particles bounced back.
Rutherford’s Nuclear Model (1911)
James Chadwick and Neutron
Experiment (1932)
Results
• Found new type of particle in the atom that
was electrically neutral – the neutron.
• Determined mass of this particle.
– Slightly larger than proton
• Mass of nucleus finally accounted for.
Chadwick Model (1932)
Structure of the Atom
Atomic Number = # of protons
+
Atomic Mass = weighted average of all isotopes measure in amu’s.
Subatomic Particles
Symbol
Relative Electric
Charge
Electron
e-
-1
0.0005486
Around nucleus
Proton
p+
+1
1.007276
Part of nucleus
Neutron
no
0
1.008665
Part of nucleus
Particle
Relative Mass
(amu)
Location in the atom
• The proton is 1800 times bigger than the
electron.
Atomic Structure
• Atoms are on the order of 10-10 m.
– 100 million atoms lined up would be 1 cm
long.
• The nucleus is very small compared to
size of the atom.
• If the atom was the size of a football
stadium…
• The nucleus would be the size of a
marble.
Closer to scale model of atom
Isotopes of carbon
Isotopes
• Atoms of the same element with different
masses.
• Atomic number = number of protons
• Mass number = number of protons +
number of neutrons
Isotopes
Hyphen Notation
Mass Number
Atomic Number
Nuclear Symbol
Atomic mass vs. molar mass
Mass of:
Measured in:
Atomic Mass
Molar Mass
1 atom of an element
1 mole of an element
amu (atomic mass unit)
grams
• Same number off of the periodic table but
different units
Weighted averages
Find the average atomic mass of copper.
Cu-63, 69.15%, 62.93 amu
Cu-65, 30.85%, 64.93 amu
Solution:
0.6915 x 62.93 amu = 43.52 amu
0.3085 x 64.93 amu = 20.03 amu
43.52 amu
+ 20.03 amu
63.55 amu