I. Atomic Models - WordPress.com. Development of Atomic Models ... How hydrogen atoms absorb and...
61
Atomic Structure Atomic Structure I. Atomic Models
Transcript of I. Atomic Models - WordPress.com. Development of Atomic Models ... How hydrogen atoms absorb and...
Atomic StructureAtomic Structure
I. Atomic Models
A. Can we “see” atoms?A. Can we “see” atoms?
Scanning tunneling microscopy (STM)
ACS: https://youtu.be/ipzFnGRfsfE
B. Development of Atomic ModelsB. Development of Atomic Models
Models ◦ Working representations of experimental facts
◦ Never 100% correct
Visual
Words
C. Origin of Atomic TheoryC. Origin of Atomic Theory
Democritus (b. 465 B.C.) ◦ Greek philosopher
◦ Matter is discontinuous
Separate, distinct particles ◦ “Atomos” – unable to be divided
Law of Definite Composition ◦ Compounds have consistent and unique parts
◦ Important for order in our universe
◦ Helps scientists make predictions
D. Dalton’s Atomic TheoryD. Dalton’s Atomic Theory
John Dalton (1766-1844) ◦ English school teacher
◦ Used data derived from experiments to form his “Billiard-Ball Model”
1. Elements are made of tiny, indestructible spheres, atoms!
2. Atoms have unique size and properties
3. Atoms can’t change into other types of atoms
4. Atoms combine to form compounds
5. Compounds always contain the same # and kinds of atoms
E. ElectronsE. Electrons
J.J. Thompson (1856-1940) ◦ Studied cathode rays
a beam of electrons emitted from the “cathode” of a high-vacuum tube
◦ Found every atom contains small, negatively charged particles
“Plum-Pudding Model” 1. Negative particles are embedded in a
positively charged substance
2. Neutral charge
3. Electrons can be removed
E. Electrons E. Electrons –– Cathode Ray Tube ExperimentCathode Ray Tube Experiment
F. ProtonsF. Protons
Ernest Rutherford (1871-1931) ◦ Cambridge University professor
◦ Studied alpha particles
Positively charged ions that are radioactive
◦ Found that alpha particles deflected when smashed into gold foil
Something in the foil had the same type of positive charge…but what?
◦ Presented the idea of an atomic NUCLEUS made of positive particles called protons
F. Protons F. Protons –– Gold Foil ExperimentGold Foil Experiment
G. NeutronsG. Neutrons
James Chadwick (1891-1974) ◦ Discovered neutrons
◦ Won a Nobel Prize in 1935 for physics
◦ Non-charged particles that add mass to the nucleus
The cartoon character “Jimmy Neutron” is named after Chadwick!
Other Models we will talk about in Other Models we will talk about in the next section!the next section!
Bohr Model
Quantum Model
Atomic StructureAtomic Structure
II. Bohr Model
A. Energy Levels for ElectronsA. Energy Levels for Electrons
Niels Bohr (1885-1962) ◦ Danish physicist
◦ Why don’t electrons fall into the nucleus?
Momentum?
◦ Studied spectroscopy
How hydrogen atoms absorb and emit light
Continuous Spectrum
Line Spectrum
Principle Energy Levels
A. Energy Levels for ElectronsA. Energy Levels for Electrons
ground state
excited state
ENERGY IN PHOTON OUT
Line-Emission Spectrum
B. Bohr Model B. Bohr Model -- 19131913
Electrons exist only in orbits with specific amounts of energy called energy levels
Therefore…
◦ Electrons can only gain or lose certain amounts of energy
◦ This energy is definite and quantized
◦ Only certain photons (light particles) are produced
B. Bohr Model B. Bohr Model -- HydrogenHydrogen
1
2 3
4 5
6 Energy of photon
depends on the difference in energy levels
Bohr’s calculated
energies matched the IR, visible, and UV lines for the H atom
C. Other ElementsC. Other Elements
Each element has a unique bright-line emission spectrum.
◦ “Atomic Fingerprint”
Helium
Bohr’s calculations only worked for hydrogen!
C. Other ElementsC. Other Elements
Atomic StructureAtomic Structure
III. Quantum Model
A. Quantum MechanicsA. Quantum Mechanics
Bohr’s model worked well for small atoms but not for larger ones
Scientists began working on a new model…
Electrons were no longer believed to orbit around the nucleus
A. Quantum MechanicsA. Quantum Mechanics
Heisenberg Uncertainty Principle
◦ Impossible to know both the velocity and position of an electron at the same time
A. Quantum MechanicsA. Quantum Mechanics
Radial Distribution Curve Orbital
Orbital -“electron cloud”
◦ 4D region in space where there is 90% probability of finding an e-
A. Quantum MechanicsA. Quantum Mechanics
Louis de Broglie (1924)
“ …the matter of an electron was not concentrated at one point but was spread out over the entire orbital.”
A. Quantum MechanicsA. Quantum Mechanics
Louis de Broglie
“If energy, under appropriate conditions, behaves as a stream of particles…could MATTER, under appropriate conditions, possibly show the properties of a wave…?”
ELECTRONS VISIBLE LIGHT
Atomic StructureAtomic Structure
IV. Electron Configuration
A. General RulesA. General Rules
States that electrons exist in principle energy levels (shells)
Divides all principle energy levels (except the first) into sublevels
Sublevels contain orbitals Orbitals contain only 2 electrons There are 4 sublevels
◦ S - spherical
◦ P - principle
◦ D - diffuse
◦ F - fundamental
“Hierarchy of organization”
A. General RulesA. General Rules
Check out figures on p.81
Study the following: ◦ Principle energy levels correspond with period numbers on the periodic table
◦ Each energy level contains specific sublevels
◦ The sublevels are arranged in a specific order: s, p, d, f
◦ Subsequent sublevels increase in energy
A. General RulesA. General Rules
Energies of sublevels ◦ Use the diagonal rule
See fig. 4B-3 on p.83
◦ Order important for constructing orbital diagrams
A. General RulesA. General Rules
Aufbau Principle p.83
◦ Electrons fill the lowest energy orbitals first.
◦ “Lazy Tenant Rule”
A. General RulesA. General Rules
Pauli Exclusion Principle p.84
◦ Each orbital can hold TWO electrons with
opposite spins.
RIGHT
WRONG
A. General RulesA. General Rules
Hund’s Rule p.85
◦ Within a sublevel, place one e- per orbital before pairing them.
◦ “Empty Bus Seat Rule”
O 8e-
Orbital Diagram p.84
• Electron Configuration p.84
1s2 2s2 2p4 B. NotationB. Notation
1s 2s 2p
• Shorthand Configuration
S:
Valence Electrons Core Electrons
[Ne] 3s2 3p4
1s2 2s2 2p6 3s2 3p4
B. NotationB. Notation
Longhand Configuration
16e-
S: 16e-
© 1998 by Harcourt Brace & Company
s
p
d (n-1)
f (n-2)
1
2
3
4
5
6
7
6
7
C. Periodic PatternsC. Periodic Patterns
C. Periodic PatternsC. Periodic Patterns
Period # ◦ energy level (subtract for d & f)
A/B Group # ◦ total # of valence e-
Column within sublevel block ◦ # of e- in sublevel
s-block 1st Period
1s1 1st column of s-block
1
2
3
4
5
6
7
C. Periodic PatternsC. Periodic Patterns
Example - Hydrogen
1
2
3
4
5
6
7
C. Periodic PatternsC. Periodic Patterns
Shorthand Configuration ◦ Core e-: Go up one row and over to the Noble Gas.
◦ Valence e-: On the next row, fill in the # of e- in each sublevel.
[Ar]
1
2
3
4
5
6
7
4s2 3d10 4p2
C. Periodic PatternsC. Periodic Patterns
Example - Germanium
Full energy level
1
2
3
4
5
6
7
• Full sublevel (s, p, d, f)
• Half-full sublevel
D. StabilityD. Stability
Electron Configuration Exceptions
Copper
EXPECT: [Ar] 4s2 3d9
ACTUALLY: [Ar] 4s1 3d10
Copper gains stability with a full
d-sublevel.
D. StabilityD. Stability
Electron Configuration Exceptions
Chromium
EXPECT: [Ar] 4s2 3d4
ACTUALLY: [Ar] 4s1 3d5
Chromium gains stability with a half-
full d-sublevel.
D. StabilityD. Stability
1
2
3
4
5
6
7
D. StabilityD. Stability
Ion Formation ◦ Atoms gain or lose electrons to become more stable.
◦ Isoelectronic with the Noble Gases.
O2- 10e- [He] 2s2 2p6
D. StabilityD. Stability
Ion Electron Configuration
◦ Write the e- config for the closest Noble Gas
◦ EX: Oxygen ion O2- Ne
Atomic StructureAtomic Structure
V. Atomic Particles
A. Subatomic A. Subatomic ParticlesParticles
POSITIVE
CHARGE
PROTONS
NEUTRAL
CHARGE
NEUTRONS
NUCLEUS
NEGATIVE CHARGE
ELECTRONS
ATOM
Most of the atom’s mass.
NUCLEUS ELECTRONS
PROTONS NEUTRONS NEGATIVE CHARGE
POSITIVE
CHARGE
NEUTRAL
CHARGE
ATOM
QUARKS
Atomic Number
equals the # of...
equal in a
neutral atom
A. Subatomic A. Subatomic ParticlesParticles
Quarks
◦ component of protons & neutrons
◦ 6 types
• 3 quarks =
1 proton or
1 neutron
B. B. Mass NumberMass Number
Mass # = protons + neutrons
• always a whole
number
• NOT on the
Periodic Table!
© Addison-Wesley Publishing Company, Inc.
CC. . IsotopesIsotopes
Atoms of the same element with different mass numbers.
C12
6
Mass #
Atomic #
• Nuclear symbol:
• Hyphen notation: carbon-12
CC. . IsotopesIsotopes
© Addison-Wesley Publishing Company, Inc.
CC. . IsotopesIsotopes
Chlorine-37
◦ atomic #:
◦ mass #:
◦ # of protons:
◦ # of electrons:
◦ # of neutrons:
17
37
17
17
20
Cl37
17
DD. . Relative Atomic MassRelative Atomic Mass
12C atom = 1.992 × 10-23 g
• 1 p = 1.007276 amu
1 n = 1.008665 amu
1 e- = 0.0005486 amu
© Addison-Wesley Publishing Company, Inc. • atomic mass unit (amu)
• 1 amu = 1/12 the mass of a 12C atom
EE. . Average Atomic MassAverage Atomic Mass
weighted average of all isotopes
on the Periodic Table
round to 2 decimal places
100
(%)(mass(mass)(%) )
Avg.
Atomic
Mass
Avg.
Atomic
Mass
EE. . Average Atomic MassAverage Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
100
(18)(0.20)(17)(0.04))(16)(99.76 16.00
amu
Avg.
Atomic
Mass
EE. . Average Atomic MassAverage Atomic Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
10
(37)(2)(35)(8)35.40 amu
F. Valence ElectronsF. Valence Electrons
Valence electrons p.39 ◦ electrons in the outermost energy level of an atom
◦ Electrons involved in chemical bonding
◦ V.E. Give elements their physical properties
◦ Use electron configuration to figure out valence electrons
EX. Argon
F. Valence ElectronsF. Valence Electrons
1s2 3p6 2s2 2p6 3s2
add up electrons in outermost energy level
= 8
1s2 2s2 2p6 3s2 = 2
EX. Nickel
3p6 4s2 3d8
electrons in outermost energy level
G. Electron Dot SymbolsG. Electron Dot Symbols
See table 4C-3 on p.94
A.k.a. Lewis Dot symbol
Represent valence electrons
S Sulfur
Al Aluminum
H. IonsH. Ions
Ions ◦ Atoms with unbalanced electric charge
Cations ◦ Positive ions
Anions ◦ Negative ions
Mg2+ F- NO3- CO3
2-
