Chem Fall Midterm

sustainability

meeting the needs of the present without compromising the ability of future generations to meet their own needs

Green Chemistry

approach to the way that products are made

• aims to reduce or eliminate the use or generation of hazardous substances

Goals of implementing green chemistry:

1. improved resource use

2. Increased energy

3. Reduced human health & environmental hazards

12 principals of Green Chemistry

1. Waste prevention

2. Atom Economy

3. Less Hazardous Chemical Synthesis

4. Designing Safer Chemicals

5. Safer Solvents

6. Design for Energy Efficiency

7. Use of Renewable Feedstocks

8. Reduce Derivitives

9. Catalysis

10. Design for Degration

11. Real-time Analysis for Pollution Prevention

12. Inherently Safer Chemistry for Accident Prevention

Catalyst

Speeds up the rate of a chemical reaction without itself undergoing a reaction

Benefits of green chemistry

1. Energy opimization: reduced temperature

2. reusable products

3. Direct Synthesis routes, reduced intermediate products and waste

4. Faster reaction time

Solvent

substances are dissolved in solvents, which are usually liquids to form solutions

uses of solvents

• dissolving solutes

• making solutions of certain concentration

• effeciently mixing a reaction

• controlling amount of energy (heating or cooling)

• Isolating + purifying product form unwanted by products

How to know if someting is “Green”?

• metrics or calculations to quantify, efficiency, waste produced, how hazardous, renewability

• compare processes to determine which is greener

What is effeciency in chemistry

• higher effeciency - least steps required to form a specific product

Biproducts

• elements produced that are not the desired product

• often waste products

• can be toxic

How to find overall reaction from elementary steps:

• take elementary steps - cancel out molecules on each side

• write remaining molecules = overall reaction

What are Green Chemistry Metrices

• metrics used to quantify efficiency or environmental performance of chemical process

Atom economy

ratio of the total molar masses of atoms in the desired product to the total molar mass of the atoms in the reaction

What is this equation for and what does each part represent

• % Atom economy

• M of desired product

• Sum of M of reactants

calculate % atom economy

92.370%

Reaction mass efficiency

ratio of mass of the desired product to the total mass of all reactants used

Goal of reaction mass efficiency

All atoms forn the reactant materals to be incorperated in the final desired product, with the best possible yield

Equation for Reaction Mass Efficiency (RME)

E-Factor

ration of the total mass of waste to the mass of desired product

Goal of E Factor

reduce waste - excess reactants, solvents and byproducts

What is this equation for and what are each elements

• E factor

• Numerator: Sum of Mass of reactants and inputs (solvents, catalysts and other inputs) - Mass of desired product

• Denominator: mass of desired product

• m1, m2 - mass of solvents

• m solvents - mass of solvents

• m catalysts - mass of catalysts

• m3 - mass of desired product

Value of % atom economy that is considered more green

larger value, 100%

Value of RME that is considered more Green

Large RME, as close to 1 as possible

Value of E factor that is considered more Green

as close to 0 as possible

Life Cycle Analysis

evaluates environmental impac of a product, process or service, including all inpusts and outputs across its entire life cycle

What does the International Organization for Standardization do?

Technology, scientific testing, working conditions, societal issues

International Organization for Standardization Life Cycle Analysis methods

• Climate issues

• Environmental toxicity

• Human toxicity

• Resource consumption

Climate issue

potential for global warming, acidification. ozone depletion, smog formation

Environmental tocxicity

potential for eutrophication, persistance, bioaccumulation, ecotoxicity

Human toxicity

potential Carcinogenicity, toxicity by ingestion or inhalation

Resource consumption

potential for abiotic depletion

Summarize components of Green Chemistry

• System thinking: - how different parts of system interact + influence others

  • ex. society, economy. environment

  • Life Cycle assessment: - inputs and outputs across life cycle

    • Ex. climate issures, enviromental toxicity, human toxicity, resource consumption

    • Green Chemistry metrices: - consider efficiency of product w/ respect to byproducts + waste

      • ex. %atom economy, RME, E factor

UN Sustainable Goals

• 17 goals to achieve world peace and prosperity

  • each has targets + indicators to monitor progress

Electromagnetic Spectrum

range of all types of electromagnetic radiation, organization by frequency, wavelength or energy

electromagentic spectrum

Important equations to know about electromagnetic spectrum

• c- speed of light in a vaccum

• v - frequency (Hz)

• E - Energy (J)

• λ - wavelength (nm = 10^-9 m)

Subatomic particles found in atom

• proton (+)

• neutron

• electron (-)

Who theorized quantun theory

Max Planck

Quantum theory (Max Planck)

• Energy is quantized (discontinuous)

• Photon is a discrete packet (quantum of energy

• E= hv

• helped discover Photoelectric Effect

• E - Energy (J)

• h - Plank’s constant (6.626 X 10^-34 Js)

• v - Frequency

Photoelectric effect

• when light of a specific wavelengt, hits a material (ex. metal plate) causing it to emit electrons

• energy is quantized

Who discovered photoelectric effect

• Heinrich Rudolf Hertz - 1887

• Albert Einstein (1905) - Nobel Prize (1921)

When will a photon be ejected (photoelectric effect)

• E_photon > E_threshold

• E_threshold - (Φ) Energy threshold that must be reached for a photon to be ejected

number of e ejected from on photon (threshold reached)

1

What happens if E_photon > Φ

excess evergy goes toward the kinetic energy

Equtions for E_photon

• KE_electon- Kinetic energy of electron

• u - velocity of ejected photoelectron

• m - mass of ejected photoelectron (9.109 × 10^-31kg)

Energy transmission in hydrogen

Emission

• higher orbital lever → lower orbital level

• exicted state → lower state

• light emited after passig through a material

• M* -> M + hv 

Absorption

• lower orbital lever → higher orbital level

• lower state → excited state

• light absorbed when passig through a material

• M + hv → M*

Equation for energy at a specifc energy level

n - energy lever

R_H = 2.179 × 10^-18J

Equations for a change in energy

• R_H = 2.179 × 10^-18J

Energy of poton equation

• always positive

Suns Emission Spectrum

• large spectrum of light

• mostly UV and infrared light

Types of UV rays emmited by the sun

• UVA

• UVB

• UVC

Which UV Rays reach earth

• UVA

• UVB

UV radiation and inteaction with atomsphere

• mostly absorbed in atosphere

  • some reach earth (UVA and UVB)

body’s response to UV Radiation

produce melanin (dark pigment) to filter UVA Radiation

Chronic exposure to UV rays can lead to…

• skin cancer

• cataracts

• genetic mutations

Electronic transitions in a molecule

absorption of light

physical sunscreens

remain on skin surface and reflect UV rays

Chemical Sunscreen

molecules that absorb UV Radiation before radiation reaches dermis (the skin)

Semiconductors

electrons must be excited from low E valence bond → higher energy conduction band

What is wave particle duality in simple terms

• waves display particle-like properties

• particles display wave like properties

Who discovered wave particle duality

• J.J. Thomson

• George Thomson

Principal quantum number (n)

• orbital energy + distance from the nucleus

• larger → further from nucleus + higher E

• n = 1,2,3…

Orbital angular momentum quantum number (l)

• orbital shape

• l = 0,1,2…(n-1)

• 0 = s, 1 = p, 2= d, 3 = f

• # l values = # subshells within a shell

magnetic quantum number

• orbital orientation

• m_l = -l …0…l

• # ml values = 2l+1

Electron Spin Quantum Number (ms)

Electrons have spin generating a magnetic field. - Value is + or – 1/2. - Pairs of electrons have no net magnetic field when spins cancel out.

Diamagnetic

All electron spins are paired. - Results in no net magnetic field (repelled by magnetic fields).

Paramagnetic

Contains one or more unpaired electrons. - Results in a net magnetic field (attracted to magnetic fields).

Aufbau Principle

Electrons occupy orbitals so that the atom's total energy is minimized (filling lower-energy orbitals first).

Pauli Exclusion Principle

Every electron in an atom has a unique set of 4 quantum numbers (no two electrons can share the exact same four quantum numbers).

Hund's Rule

Orbitals of the same energy (degenerate orbitals) are occupied singly with parallel spins before any pairing occurs.

Lewis definition of bonding

The transfer or sharing of outer electrons usually to acquire a stable configuration.

Ionic bonding

The transfer of electrons, usually occurring between a metal and a non-metal.

Typical elements involved in ionic bonding

A metal and a non-metal.

Covalent bonding

The sharing of electrons, often to attain an octet of electrons, usually between two non-metals.

Goal of covalent bonding for atoms

Often to attain an octet of electrons.

Elements typically involved in covalent bonding

Two non-metals

Lewis structure representation of electrons and bonds

Shows all electrons as equivalent, with bonds depicted as lines.

Electronegativity (EN)

An atom's ability to compete for electrons in a bond.

Periodic trend for electronegativity

EN increases across a period and up a group.

Element with the highest electronegativity on the Pauling scale

Fluorine (F), with a value of 4.0.

Determining factor for bond polarity

Electronegativity difference

Electronegativity difference threshold for an ionic bond

∆EN > 1.9.

Electronegativity difference range for a polar covalent bond

0.5 ≤ ∆EN < 1.9

Electronegativity difference range for a pure covalent bond

∆EN < 0.5

Polar covalent bonds 

• Unequal sharing of e- 

• Indicated by polar arrow and partial charges 

Electrostatic Potential Map:

• Scale: Blue – positive, red – negative  

• Shows were electron density is 

Lewis Structures

• Show bonding and non bonding electrons, and formal charges 

• Complete shells – combination of bonding and non bonding e- pairs (lone pairs) 

A complete shell is an octet with the following exceptions

• hydrogen is satisfied with 1 electron pair

• beryllium can be satisfied with 3 electron pairs

• elements in perions 3 and beyond can have expanded octets if involved as a central atom

Steps for drawing a lewis structure

1. Count total number of valence electrons (add for negative charge, subtract for positive charge).

2. Draw skeletal structure (least electronegative atom in the center; Hydrogen and Fluorine are always terminal).

3. Use remaining electrons to complete octets of terminal atoms (or 2 electrons for hydrogen).

4. Subtract all electrons used and place any remaining electrons on the central atom (can lead to expanded octets).

5. Calculate formal charges (FC) on each atom:

   1. FC = (Valence e - ½ bonding e - nonbonding e-)

6. Minimize formal charges by creating multiple bonds using non-bonding electrons (typically happens when neighboring atoms have opposite charges)

7. Ensure all atoms have an allowed electron count (C, N, O, F must obey octet rule).

8. Charged molecules: Negative formal charge typically on the most electronegative atom; positive formal charge typically on the least electronegative atom.

Resonance structure

1+ valid Lewis structures that represent the electron bonding of a molecule or ion when a single structure cannot fully capture it (think isotopes for shapes of molecules)

Resonance hybrid

the single, true chemical structure of a molecule or ion that results from combining all valid contributing Lewis structures

• charges are an average of all equivalent resonance structures

Average formal charge for an atom

(total charges on an atom)/ total # of that atom

Average bond order

total # of bond orders / total # of places the bond is formed

bond order relates to _____

length of bond

covalent bonf length

approximate distance between 2 nuclei involved in a covalent bond

homolysis

bond dissociation energy