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The AtomDemocritus
Invisible
Immortal
Indivisible units
Aristotle
Continuous matter
Joseph
Proust
(1754 – 1826)Law of Definite Proportions
Law of Definite
ProportionsCopper Carbonate:
Regardless of the source, a compound always has the same proportion of elements
Law of Definite
Proportions
Copper Carbonate:
CuCO3 -> Copper + Carbon + Oxygen
Law of Definite
ProportionsCopper Carbonate:
CuCO3 -> Copper + Carbon + Oxygen
51.36% 9.72% 38.85%
Antoine Lavoisier
Law of Conservation of Mass
Antoine Lavoisier
Law of Conservation of Mass
Antoine Lavoisier
Accounting for Oxygen gas
John Dalton
Law of MultipleProportions
Law of Multiple Proportions
CO and CO2
H2O and H2O2
NH3 and N2H4
Law of Multiple Proportions
NH3 and N2H4
N2 + 3 H2 ---> NH3
N2 + 2 H2 ----> N2H4
Law of Multiple Proportions
NH3 and N2H4
N2 + 3 H2 ---> NH3
28 g 6 g 34 g
N2 + 2 H2 ----> N2H4
28 g 4 g 32 g
Law of Multiple Proportions
When elements combine to form more than one compound, different masses of one element compared to the mass of the other element are small whole number ratios.
Law of Multiple Proportions
CO and CO2
2 C + O2 ---> 2 CO
24 g 32 g 56 g
C + O2 ----> CO2
12 g 32 g 44 g
Dalton’s Five Principles
Matter is made of atoms
All atoms of one element are the same
Atoms of different elements are different
Atoms combine to form compounds
Atoms are rearranged in chemical reactions but not created nor destroyed
What is an Atom?
Cathode Rays
William Crookes
CRTs
Stream of Charged Particles
How much smaller?
Robert Millikan found that the particles were 1/1840 the size of the Hydrogen atom
Plum Pudding Model
Negatively charged particles embedded in a positively charged ball of matter.
The Discovery of ElectronsJ.J. Thomson found that the cathode ray particles were much smaller than the H atom
Rutherford’s Gold Foil experiment
Ernest Rutherford directed alpha particles at gold foil
Planetary Model
The Discovery of the Neutron
1932
Finds particle with no charge that has a mass of 1 atomic mass unit
Atomic Number
Identification Number
NUMBER
OF PROTONS
Atomic Numbers
Atomic Masses
Number of Protons (ATOMIC NUMBER)
+
Number of Neutrons
ATOMIC MASS
Dalton’s Atoms
Atoms
Atomic Symbols
Mass Number A = Sum of protons and neutrons
Atomic number, Z = # of protons
Atomic Symbols
Mass Number A = Sum of protons and neutrons
Atomic number, Z = # of protons
The number of neutrons for any atom will be the difference between A and Z (A – Z = # neutrons)
Writing Atomic Symbols
Symbol Atomic mass
protons neutrons
22 ???? ?????
????? 20 26
11 ???? 6
???? ????? ??????
€
1022Ne
€
2046Ca
€
511B
€
3064Zn
Writing Atomic Symbols
Symbol Atomic mass
protons neutrons
22 10 12
46 20 26
11 5 6
64 30 34
€
1022Ne
€
2046Ca
€
511B
€
3064Zn
Isotopes
Same atomic number
Different Mass number
Different # neutrons
Isotopes
Relative abundance
Br-79 Br-81
50.697% 49.317%
Bromine:
35 protons
Relative abundance
Br-79 Br-81
50.697% 49.317%
Bromine:
35 protons
(79)(0.50697) + (81)(0.49317) =
40 + 39.9 = 79.9
Listed Atomic Massed areWeighted Averages
Br79.9
35
Same atomic mass??
€
2860Ni
2960Co
What about Electrons?
Why don’t electrons crash into the Nucleus?
Bohr Model of the Atom
Niels Bohr1913
Allowable Energy Transitions
Electromagnetic Spectrum
Properties of Waves
As Wavelength increases, Frequency decreases.
Wavelength x Frequency = λ x ν = velocity of Light = c
Emission Spectra
Atomic Emission Spectra
Schrödinger probability functions
S orbital
P orbitals
3 types of porbitals
D orbitals
5 types of d orbitals
How can electrons be ordered?
Energy Levels
Aufbau (Building up)
Principle
An electron must fill the orbital
With the lowest energy first.
Energy Levels
Orbital Shapes
S orbitals
P orbitals
Orbital Shapes
D orbitals
F orbitals
Quantum Numbers
n Principal Quantum numberEnergy Level
l Angular Momentum Quantum Shapenumber
n Magnetic Quantum numberSpin
Spin States
Pauli exclusion Principle
No two electrons in the same atom may have the same set of four quantum numbers;
Electrons in the same orbital must have opposite spins.
Hund’s Rule
Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron. All electrons in singly occupied orbitals must have the same spin state
Groups
Dozen
Pair Quartet
The Mole
# of atoms in 12 grams of Carbon-12 atoms
Molar Mass
Mass of one MOLE of pure substance
Helium: 4.00 grams -------> 4 grams per mole
Lithium 6.94 grams ---------> 6.94 grams per mole
Mercury 200.59 grams -------> 200.59 grams per mole
Size of the Atom
Diameter of an atom = 10-10 m
250,000,000 atoms in One Inch
Size of the Atom
1 atomic mass unit = mass of one proton, neutron
= 1.66 x 10-24 grams
Avogadro’s Number
There are 6.02 x 1023 particles in a mole of any substance.