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CHEM 130 Chapter 2: Quantum Mechanical Model
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  • Course
  • CHEM 130 (CHEM130)
  • Institution
  • University Of Michigan - Ann Arbor

Class notes for Chapter 2: Quantum-Mechanical Model in the class General Chemistry: Macroscopic Investigations and Reaction Principles (CHEM 130) at the University of Michigan. Subjects covered include wave natures of light and matter, electromagnetism, diffraction, the particle nature of light, Bo...

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Document information

  • August 2, 2024
  • 19
  • 2022/2023
  • Class notes
  • Carol castaneda
  • All classes

Subjects

  • light
  • lightwaves
  • electromagnetic
  • bohr model
  • wave nature
  • de broglie wavelength
  • uncertainty principle
  • indeterminacy
  • quantum mechanics
  • atomic orbital
  • orbitals
  • s orbital
  • p ori
  • probability distribution map

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  • University Of Michigan - Ann Arbor
  • CHEM 130 (CHEM130)
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Schrodinger’s Cat
●Atoms/Particles are unimaginably small
○One speck of dust has more electrons than the number of people who have existed on Earth ever
●Quantum particles (such as electrons) can be in two different states at the same time ○An unobserved quantum atom can be both emitting a particle and not emitting a particle at the same time
■Act of observing/measuring the particle forces the atom into one state or the other
●Erwin Schrodinger: attempted to explain that quantum states can’t transfer to the macroscopic world with a thought experiment in which a cat is put into a chamber that has radioactive atoms. The chamber has a mechanism that, when an energetic particle is emitted by a radioactive atom, causes a hammer to break a flask that releases a poison and kills the cat.
○If the chamber is closed, the system is unobserved → radioactive atom is in a state in which it has emitted the particle and not emitted the particle with equal probability
■The cat is both dead and alive
○Demonstrated how quantum strangeness does not transfer to macroscopic world
●Quantum-Mechanic Model: a model that explains behavior of absolutely small particles
such as electrons and photons
The Nature of Light
●Light has many of the same characteristics as electrons
The Wave Nature of Light
●Electromagnetic Radiation: form of energy embodied in oscillating electric and magnetic fields
○Magnetic field: region of space where a magnetic particle experiences a force
○Electric field: region of space where an electrically charged particle experiences
a force
●We characterize waves by amplitude and wavelength
○Amplitude: vertical height of a crest of a wave
■Measure of wave intensity/brightness
■Greater amplitude → greater brightness
○Wavelength (λ - lambda): distance between adjacent crests of a wave
■Measured in units like meters or micrometers
■λ: Greek letter lambda
■Wavelength determines color ○Frequency ( - nu): 𝜈number of cycles that pass through a stationary point in a given period of time
■Units are cycles per second (cycle/s), s-1, or hertz (defined as 1 cycle/s)
■Directly proportional to the speed of the wave, inversely proportional to the wavelength
○Speed of light: C = 2.998 x 108 m/s = 𝜈λ
■C is the speed of light
■C and λ expressed in same unit of distance
○
●Visible Light: light that can be seen by the human eye
○Different colors = different wavelengths
○White light has a spectrum of colors
○Red light has the longest wavelength (750 nm), violet has the shortest (400 nm)
●When we see color, the object is absorbing every color except the one reflected back at our eyes
EX PROBLEM
What is the wavelength of a radio wave w frequency of 1.23 x 107 s-1?
Given: = 𝜈1.23 x 107 s-1
Find: λ
Strat: C = 𝜈λ → the units are (m)(1/s) → (m/s)
C = 𝜈λ → divide by 𝜈 on both sides → C/ 𝜈 = λ
Solve:λ = (2.998 x 108 m/s) / (1.23 x 107 / s) → s cancels out → 24.4 m
The Electromagnetic Spectrum
●Electromagnetic Spectrum: range of wavelengths of all possible electromagnetic radiation
○Main regions range from 10-15 m (gamma rays) to 105 m (radio waves)
■Visible light is only a small region in the middle ○
●Short-wavelength light inherently has greater energy than long-wavelength light
The Electromagnetic Spectrum (shortest to longest wavelength)
●Gamma Ray: form of electromagnetic radiation with the shortest wavelength and the highest energy
○Produced by the sun, stars, and some unstable atomic nuclei
○Excessive exposure is dangerous because they can damage biological molecules
●X-Rays: form of electromagnetic radiation with wavelengths slightly longer than gamma rays; used to image bones and internal organs
○Able to pass through many substances that block visible light
○Some annual exposure to X-rays is harmless but overexposure can increase risk of cancer
●Ultraviolet (UV) Radiation: electromagnetic radiation with slightly smaller wavelengths than visible light
○Component of sunlight that produces tan/burn
○Not as strong as gamma or X-rays but can damage biological molecules, increase risk of skin cancer, and cause premature wrinkling of the skin
●Visible Light: electromagnetic radiation with frequencies that can be detected by the human eye
○Does not have enough energy to damage biological molecules
○Causes certain molecules in our eyes to change shape and send a signal to our brains that lets us see it
●Infrared (IR) Radiation: electromagnetic radiation emitted from warm objects
○Invisible to our eyes but can be detected by infrared sensors
■Used in night vision technology to help people see in the dark
○We can feel it as heat
●Microwaves: electromagnetic radiation with wavelengths longer than IR radiation
○Used in radar and microwave ovens
○Lower energy than other lights but efficiently absorbed by water
■Can easily heat substances that contain water
●Radio Waves: form of electromagnetic radiation with the longest wavelengths and smallest amount of energy

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