Properties of Matter
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Transcript of Properties of Matter
![Page 1: Properties of Matter](https://reader036.fdocuments.in/reader036/viewer/2022070400/568134df550346895d9c116e/html5/thumbnails/1.jpg)
Properties of Matter
Our goals for learning:
• What is the structure of matter?
• What are the phases of matter
• How is energy stored in atoms?
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What is the structure of matter?
Atom Nucleus
ElectronCloud
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Atomic Terminology
• Atomic Number = # of protons in nucleus • Atomic Mass Number = # of protons + neutrons
• Molecules: consist of two or more atoms (H2O, CO2)
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Atomic Terminology
• Isotope: same # of protons but different # of neutrons. (4He, 3He)
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What are the phases of matter?
• Familiar phases: – Solid (ice)– Liquid (water)– Gas (water vapor)
• Phases of same material behave differently because of differences in chemical bonds
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Phases of Water
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Phase Changes
• Ionization: Stripping of electrons, changing atoms into plasma
• Dissociation: Breaking of molecules into atoms
• Evaporation: Breaking of flexible chemical bonds, changing liquid into solid
• Melting: Breaking of rigid chemical bonds, changing solid into liquid
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How is energy stored in atoms?
• Electrons in atoms are restricted to particular energy levels
Ground State
Excited States
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Energy Level Transitions
• The only allowed changes in energy are those corresponding to a transition between energy levels
AllowedNot Allowed
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Learning from Light
Our goals for learning:
• What are the three basic types of spectra?
• How does light tell us what things are made of?
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What are the three basic types of spectra?
Continuous Spectrum
Emission Line SpectrumAbsorption Line Spectrum
Spectra of astrophysical objects are usually combinations of these three basic types
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Three Types of Spectra
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Continuous Spectrum
• The spectrum of a common (incandescent) light bulb spans all visible wavelengths, without interruption
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Thermal Radiation
• Thermal radiation
• Blackbody radiation
• Continuous spectrum
We’ve already seen some laws from this theory…
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How does light tell us the temperatures of planets and stars?
Thermal Radiation
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Thermal Radiation
• Nearly all large or dense objects emit thermal radiation, including stars, planets, you…
• An object’s thermal radiation spectrum depends on only one property: its temperature
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Properties of Thermal Radiation1. Hotter objects emit more light at all frequencies per
unit area.
2. Hotter objects emit photons with a higher average energy.
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Wien’s Law
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Thought QuestionWhich is hotter?
a) A blue star.
b) A red star.
c) A planet that emits only infrared light.
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Thought QuestionWhich is hotter?
a) A blue star.
b) A red star.
c) A planet that emits only infrared light.
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Thought QuestionWhy don’t we glow in the dark?
a) People do not emit any kind of light.b) People only emit light that is invisible to our
eyes.c) People are too small to emit enough light for us
to see. d) People do not contain enough radioactive
material.
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Thought QuestionWhy don’t we glow in the dark?
a) People do not emit any kind of light.b) People only emit light that is invisible to our
eyes.c) People are too small to emit enough light for us
to see. d) People do not contain enough radioactive
material.
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Emission Line Spectrum
• A thin or low-density cloud of gas emits light only at specific wavelengths that depend on its composition and temperature, producing a spectrum with bright emission lines
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Absorption Line Spectrum
• A cloud of gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum
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How does light tell us what things are made of?
Spectrum of the Sun
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Chemical Fingerprints
• Each type of atom has a unique set of energy levels
• Each transition corresponds to a unique photon energy, frequency, and wavelength
Energy levels of Hydrogen
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Chemical Fingerprints
• Downward transitions produce a unique pattern of emission lines
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Chemical Fingerprints
• Because those atoms can absorb photons with those same energies, upward transitions produce a pattern of absorption lines at the same wavelengths
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Chemical Fingerprints
• Each type of atom has a unique spectral fingerprint
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Chemical Fingerprints
• Observing the fingerprints in a spectrum tells us which kinds of atoms are present
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Example: Solar Spectrum
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Energy Levels of Molecules
• Molecules have additional energy levels because they can vibrate and rotate
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Energy Levels of Molecules
• The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated
• Many of these molecular transitions are in the infrared part of the spectrum