Download ATOM

Chapter 2.1-2.4
& definition of moles
Atoms, Molecules, and Ions
Atomic Theory (Dalton)
1. Elements are made up of atoms (Na,
K, H, etc.)
2. Atoms of same elements have same
properties
3. Atoms are neither created nor
destroyed in a chemical reaction
(Law of Conservation of mass)
4. Compounds are formed by
combinations of elements in fixed
ratios.
H2O  2 H, 1 O
• What makes an atom?
– How can one get that information?
• What makes an egg?
– How can you get that information?
ATOM
Electron (e)
Charge
Proton (p)
Neutron (n)
-1
+1
0
1/1837
1
1
(au)
Mass
(au)
1 amu = 1.66 x 10-24 g
Discovery & Characterization of
the electron (e)
• Cathode Ray
(-) charges
electrons
Thompson’s Experiment
• With electrically charged plates and
a magnet
• Charge/mass ratio for an electron
– (e/m) = 1.76 x 108 Coulomb/g (or
C/g)
Millikan oil-drop experiment
Charge of e- = 1.60 x 10-19 Coulomb (C)
Mass of e- = 9.10 x 10-28 g
Radioactivity
• Spontaneous emission of radiation
U
238
92
α ( 24He)
β (
γ (
•
e )  electron
0
1
)
0
0γ
U Note: 238 is # protons + #
238
92
neutrons, 92 is # protons
• α is attracted to (-) plate and hence
must contain (+) charge
Rutherford’s Experiment
• Atom
– Protons (p), Neutrons (n), and
Electrons (e-)
• How are they together?
• Are they uniformly spread over?
Rutherford’s Experiment
•α-Particles are allowed to strike a gold
plate
»Most particles go through
»A few go backward
Rutherford’s Experiment
• Can we predict what is going on in
Rutherford’s Experiment?
• Why do α –particles (used as balls) go
through undeflected?
Rutherford’s Experiment
• Conclusion
– An atom is mostly made up of empty
space (like an open door) with a
massive nucleus (like a concrete wall),
occupying a very small volume.
– Nucleus has protons and neutrons,
electrons revolve outside.
Isotopes, Atomic Number, and
Mass Number
• Atomic number = Number of
Protons
• Mass number = # Protons + #
Neutrons
• Can you define “isotopes”?
– Same elements?
– How are they different?
Isotopes, Atomic Numbers, and Mass
Numbers
H
1
1
2
1
H
H
3
1
•Here is an example of Isotopes.
•Remember that the top number is the mass
# and the bottom number is the atomic #.
Average Atomic Mass
• Avg. mass = P1M1 + P2M2 + …
–
–
–
–
P1 = % abundance for Isotope 1
M1 = Mass for Isotope 1
P2 = % abundance for Isotope 2
M2 = Mass for Isotope 2
Refer to Problem 29 (Pg. 72)
Mass Spectrometer
• Obtain atomic and molecular
weights
• Need gaseous samples
• Ionization of sample by high
energy electrons
• Pass gaseous ions through poles of
a magnet
• For ions carrying the same charge,
more massive particles will be less
deflected than the less massive
particles. Thus, mass separation
takes place.
Mole & Number
• 1 thousand = 103 = 1000
• 1 million = 106
• 1 mole = 6.022 x 1023 (Avogadro’s
number)
• 1 mole H atoms = 6.022 x 1023 H atoms
• 1 mole H2O molecules = 6.022 x 1023
H2O molecules
Mole & Gram (Molar Mass)
(Remember: M-g-P = mole-gram-Periodic
Table)
• 1 mole C weighs 12.0107 g ≈ 12.0 g C
atoms
– Found on the Periodic Table
• 1 mole H weighs 1.00794 g ≈ 1.00 g H
atoms
• 1 mole H2O = 2(1.00794) + 15.9994 ≈
2 + 16 = 18 g H2O molecules