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Chem 027 Workshop Tuesday 2-4 pm Workshop Reminders ● Workshop mandatory unless professor says otherwise ● Attend one workshop session per week (full two hours) ○ Does not matter which workshop session you attend ● Attendance is taken at the end of workshop→ Google form ● If you have questions regarding attendance errors email Dr. Pantouris Contact Info Email: [email protected]fic.edu Phone #: (661) 859-9129 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