Download Chapter 4: The Structure of the Atom 4.1 The

Chapter 4:
The Structure of the Atom
4.1 The Structure of the Atom
•Democritus (460-370 B.C.) was the
first to use the term atom. He, and the
atomists, described atoms as the
indivisible particle.
•Aristotle (384-322 B.C.) critisized
Democritus by asking what held atoms
together, developed the idea of earth,
fire, water and wind as the 4 elements
of all natural substances.
4.1 Continued
• John Dalton, (1766-1844) proposed, in 1803, the
atomic theory.
1-Matter is composed of small particles called atoms.
2-Atoms are indivisible and indestructable.
3-Atoms of given elements are identical.
4-Atoms of a specific element are different from atoms
of other elements.
5-Different atoms combine in simple whole number
ratios to form compounds.
6-In chemical reactions, atoms are separated,
rearranged or combined.
The red texted items were mistakes.
Conservation of Mass
• Mass is not created nor is it destroyed, it is
only conserved.
4.2 Defining the Atom
• The scanning tunneling microscope can actually
image individual atoms.
• Sir William Crookes and JJ Thomson discovered the
electron...this exposed the flaw of the 'indivisible
atom' of Dalton.
• The cathode ray tube was used to study the electron.
• JJ Thomson discovered the charge-to-mass ratio and
Robert Millikan discovered the charge of the electron,
with the oil-drop experiment.
• Using the charge and charge to mass ratio, Millikan
estimated the electon mass as 9.1 x10-28 grams.
4.2 Models of the Atom
• JJ Thomson developed the plum-pudding
model of the atom.
• Rutherford developed his concept of the
nucleus with the gold foil experiment.(txt p 112)
• Sir James Chadwick discovered the neutron in
1932.
Rutherford's Experiment
Properties of Subatomic Particles
•
•
•
•
Particle Relative Charge
Electron
−1
Proton
+1
Neutron
0
Relative Mass
1/1840
1
1
4.3 How Atoms Differ
• Atomic Number is the number of protons in an
atom....since atoms are neutral, it is also the
number of electrons.
• Mass Number is the number of protons and
neutrons added together.
• Isotopes are the different forms of the same
atom, with different numbers of neutrons and
different masses...the same atoms always have
the same atomic number.
Mass of Atoms
• The Atomic mass unit is used to provide a
relative mesure of mass of atoms and
subatomic particles.
• Atomic mass is the weighted average of all
isotopes of an atom.
1. Multiply the mass of an isotope times the
decimal form of its abudance.
2. Repeat for each isotope.
3. Add the totals of each isotope to get the
atomic mass.