Download Chem 027

Chem 027
Workshop
Tuesday 2-4 pm
Week 1: Chemical Kinetics
Reaction rate:
● Change in concentration of a reactant or product per unit of time
● Rate of a reaction is not a constant
For general reaction A→ B,
* when time increases, concentration decreases
Week 1: Chemical Kinetics
Rate Law:
● Used to predict the relationship between the rate of a reaction and the
concentration of the reactants
→ For reaction
aA + bB → dD + eE, rate= k[A]n[B]m
k= rate constant
m, n= order of the reaction
k, m, n are determined experimentally
m, n are not related to reaction coefficient
Concentration of products do not appear in the rate law
Week 1: Chemical Kinetics
● Two forms of Rate Law:
→ Differential Rate Law (Rate Law): expresses how rate depends on concentration
Ex: rate= k[A]n[B]m
→ Integrated Rate Law: expresses how concentrations depend on time
Ex: first order, second order, zero order
When there are two different temperatures given use:
Week 2: Nuclear Chemistry
REMINDERS!!
Isotopes: same atomic number (protons), different mass # due to different #
of neutrons
Radioactive decay: nuclei undergo decomposition to form different nuclei
- Many nuclei are radioactive and decompose to other nuclei
- Only 277 of the known 2000 nuclides are stable with radioactive decay
Types of Radioactive Decay
Alpha particle production
- Alpha particles are helium atoms
Beta particle production
- Beta particles are electrons
- Net effect of beta particle production is to change a neutron to a
proton
- Although beta particle is an electron, emitting nucleus does not contain
electrons
Gamma Ray production
- Gamma rays are high energy photons
- No mass, no charge
- Always there, not always shown
- Accompanies nuclear decays and particle emissions
- Acts as a way for nucleus to release excess energy
Types of Radioactive Decay
Positron Production
- Antiparticle of an electron
- Net effect to change proton to neutron
- When a positron collides with an electron, the particulate matter is
changed to high energy photons
Electron Capture
- Process where one of the inner orbital electrons is captured by the
nucleus
Radioactive Decay Series
- Some radioactive nuclei cannot reach a stable state through a single
decay process so a decay series occurs until a stable nuclide is
formed
Rules for Nuclear Reaction Equations
1. A&Z must be conserved
2. Sum of mass number must be the same on both sides
3. Sum of atomic number must be the same on both sides
Think basic algebra!!
Kinetics of Radioactive Decay
First order process→ same as first order rate law
Rate of decay:
ln(N/N0) = -kt
or
ln(N/N0) = kt
N= # of radioactive atoms
N0= initial # of radioactive atoms
k= rate constant
t= time
Half life:
t1/2= ln(2)/k = 0.693/k
k= rate constant
Week 3: Quantum Mechanics
What is quantum mechanics?
- Deals with the behavior of matter and light on the atomic
and subatomic scale
The Nature of Matter
- ALL matter exhibits both particulate and wave properties
- Large matter exhibits mainly particulate properties (ex.
baseball)
- Very small matter exhibits predominantly wave
properties (ex. photons)
- Intermediate matter exhibits BOTH (ex. electrons)
The Dual Nature of Light
- Light (electromagnetic radiation) is made up of particles
called photons
- Exhibit both wave and particulate properties (primarily
wave)
Nature of Waves
- Longer wavelength → lower frequency→ lower energy
- Shorter wavelength→ higher frequency→ higher energy
- Wavelength λ (m)
- Peak to peak, trough to trough,
middle to middle
- Frequency 𝑣 (Hz or s-1)
- Velocity (speed)
- v or c (m/s)
- c → vacuum → speed of light
- Amplitude (intensity, I)
c= λ𝑣
𝑣= c/λ
λ=c/𝑣
de Broglie’s Equation
Louis de Broglie derived an equation that related the wavelength
with the momentum of a particle
λ=h/mv
h: Planck’s constant→ 6.626 x 10-34 J s
m: mass
v: velocity
Photoelectric Effect
Discovered by Heinrich Hertz in 1887, explained by Einstein in 1905
- Number of electrons emitted depends on the intensity of the
incident light
- KE of the emitted electrons depend on the frequency of the
light
In simpler terms→ electron emission when light hits a material
The Photoelectric Effect
Einstein’s Explanation→ proposed that electromagnetic
radiation is quantized
KEelec=1/2mv2=hv-hvo
m= mass of electron
v= velocity
hv= incident light with E
hvo= threshold energy Eo→ minimum energy to eject an eEinstein’s equation
Ephoton= hv= h(c/λ)
Bohr Model
Niels Bohr developed quantum model for the H-atom in 1913
- Electron in a H-atom moves around the nucleus only in certain
allowed circular orbits
- Works for 1 electron systems (hydrogen and ions with 1 electron)
- Presence of other electrons repels other electron and
interfere with energy level
E = -2.178 x 10-18 J (Z2/n2)
ΔE = -2.178 x 10 -18J (Z2/nf2- Z2/ni2)
n= 1, 2, 3, 4…∞, when n = ∞, E = 0
Z= atomic number
Energy change between two levels
Applies to all one electron systems,
not just H
Heisenberg Uncertainty Principle
There is a fundamental limit to how precisely one can know
both the position and momentum of a particle at a given time
𝚫x • 𝚫p ≥ h/4𝛑
𝚫p = 𝚫(mv)
𝚫x = uncertainty in position
𝚫p = uncertainty in momentum
h = Planck’s constant = 6.626 x 10-34 m2kg/s
The more precisely a particle’s position is known, the less
precisely we know its momentum (vice versa)
Workshop Week 4:
Atomic
Theory
Particle in a One-Dimensional Box
n= quantum number→ 1, 2, 3, 4,...
h= Planck’s constant
m= mass
L= length of box
Quantum Numbers
n= principal quantum number
→ tells the energy and the size of the orbital
→ n= 1, 2, 3, 4, … (principal shell)
ℓ= angular momentum quantum number
→ tells the shape and the type of orbital
→ n-1= 0, 1, 2, 3, 4, … (subshell)
ml= magnetic quantum number
→ tells the orientation of the orbital in space
→ ml= -ℓ…0…+ℓ
ms= spin quantum number
→ determined from the experiment
→ +½, -½
Electrons
Aufbau Principle
- electrons fill lower energy levels before higher energy
Pauli Exclusion Principle
- no two electron in an atom may have all four quantum
numbers
- Only two electrons can occupy the same orbital and must
have opposite spins
Hund’s Rule
- every orbital in a subshell is singly occupied before being
filled doubly
Electron Configuration
Trends in Atomic Properties
Workshop Week 5:
Chemical
Bonding
Types of Chemical Bonds
→ Chemical
bonds: hold groups of atoms together so atom can
function as a unit
→ Ionic bonds: result from a transfer of electrons from one
atom to another
→ Covalent bonds: result from sharing electrons between
atoms
→ Polar covalent bonds: result from unequal sharing of
electrons between atoms
Electronegativity
→ ability of atoms to attract electrons
Relationship between electronegativity and bond type:
Electronegativity
difference in bonded atoms
Bond Type
Zero
Covalent
Intermediate
Polar Covalent
Large
Ionic
Electronegativity
Relationship between electronegativity and bond polarity:
Bond polarity→ different electronegativities between atoms
- The greater the difference in electronegativities, the greater
the polarity
Dipole moment→ occurs due to a separation of charges, the atom
with greater electronegativity pulls electron density towards it
- The greater the difference in electronegativities, the greater
the dipole moment
Equation:
DP (in Debye) = charge x distance
Enthalpy Change
→ bond energy: measure of bond strength and the amount of
energy needed to break molecular bonds
- can be used to calculate a reaction’s enthalpy of change
Equation:
ΔH= ΣD (bonds broken) - ΣD (bonds formed)
Rules for Writing Lewis Structures
1. Sum the valence electrons from all atoms
2. Use a pair of electrons to form a bond
3. Apply duet rule for H and Octet Rule for other second
period elements
4. Multiple bonds can be used to fulfill Octet Rule
Exceptions to Octet Rule:
- Be and B can have less than 8 electrons
- Third row and heavier elements can have more than 8
electrons
Formal Charge
- Sum of all charges
FC = # of valence electrons - number of assigned electrons
Resonance
- When more than one valid Lewis structure can be written
for a molecule
- Arrangement of atoms is the same, movement of
electrons differs
- Hypothetical forms, actual structure is a hybrid of all
resonance structures
VSPER Model
Valence Shell Electron-Pair Repulsion Model
- Structure around an atom is described by minimizing
electron repulsion
- Bonding and nonbonding electron pairs positioned as far
apart as possible
- Lone pairs require more room and compress angles between
bonding pairs