Spectroscopy Interaction between atoms and light.

Light Light is the key to understanding the modern atom. Light is the key to understanding the modern atom. Has both wave and particle properties depending on how you measure it. Has both wave and particle properties depending on how you measure it. A packet of light is called a photon. A packet of light is called a photon. Source: Wikimedia Commons

All electromagnetic radiation is light. All electromagnetic radiation is light. Source: North Carolina End-of-Course Chemistry Reference Table

Wavelength Wavelength – λ (lambda) – the distance between two equivalent points on a wave. Wavelength – λ (lambda) – the distance between two equivalent points on a wave. Measured in length units, (m, nm, pm, etc.) Measured in length units, (m, nm, pm, etc.) Source: library.thinkquest.org, Used by permission

Characteristics of Light Frequency – ν (nu) – the number of times a particular point on a wave passes by an observer in one second. Frequency – ν (nu) – the number of times a particular point on a wave passes by an observer in one second. Measured in Hertz, Hz = 1/s Measured in Hertz, Hz = 1/s Source: Wikimedia Commons

Relationship Between Frequency and Wavelength Wavelength and Frequency are Inversely Related Wavelength and Frequency are Inversely Related As one goes up the other goes down. As one goes up the other goes down. c = λν c = λν c = speed of light = x 10 8 m/s Source: Wikimedia Commons

Characteristics of Light There are a wide range of frequencies and wavelengths of light. There are a wide range of frequencies and wavelengths of light.

Characteristics of Light One photon of light can transfer only a specific amount of energy One photon of light can transfer only a specific amount of energy The energy of one photon, E = hν The energy of one photon, E = hν E = energy of one photon E = energy of one photon h = Planck’s constant, x Js h = Planck’s constant, x Js v = frequency v = frequency Energy is proportional to frequency Energy is proportional to frequency

Which light can do the most damage to you? Which light can do the most damage to you? Short wavelength and high frequency has the highest energy Short wavelength and high frequency has the highest energy Source: North Carolina End-of-Course Chemistry Reference Table

Light Wavelength and Frequency are inversely related. Wavelength and Frequency are inversely related. Frequency and Energy are directly related. Frequency and Energy are directly related. Wavelength and Energy are inversely related. Wavelength and Energy are inversely related.

Practice Problems The newly developing LTE cell networks are in the 700MHz band. Verizon’s uplink band starts at 777MHz. What is the wavelength of a photon of this light? The newly developing LTE cell networks are in the 700MHz band. Verizon’s uplink band starts at 777MHz. What is the wavelength of a photon of this light? What is the energy of a photon transmitted at 777MHz? What is the energy of a photon transmitted at 777MHz?

Atomic Spectra Emission Spectrum Emission Spectrum Spectrum of light emitted by a substance when energy is added. Spectrum of light emitted by a substance when energy is added. Flame Tests Flame Tests Discharge Tubes Discharge Tubes

Atom Emission Spectra

Simple Initial Model Hydrogen Atom Hydrogen Atom Only one electron Only one electron Therefore, quantum mechanical calculations simplify tremendously. Therefore, quantum mechanical calculations simplify tremendously. All subshells are degenerate with each other in the same shell. All subshells are degenerate with each other in the same shell. We can just worry about transitions from one shell to another shell with out caring about what subshell it ends up in. We can just worry about transitions from one shell to another shell with out caring about what subshell it ends up in.

Source: North Carolina End-of-Course Chemistry Reference Table Specific Energy Levels n = 1,2,3,4, etc. Transition from “excited” state to “ground” state and the light produced by the transition.

Multi-Electron Atoms Subshells are not all the same energy. Subshells are not all the same energy. Determining the transitions becomes much harder. Determining the transitions becomes much harder.

Emission Spectrum 670nm = 1s 2 2p 1 to 1s 2 2s 1 670nm = 1s 2 2p 1 to 1s 2 2s 1 Excited state to ground state Strongest line and gives lithium flame test its color. 610nm = 1s 2 3d 1 to 1s 2 2p 1 610nm = 1s 2 3d 1 to 1s 2 2p 1 Excited state to lower excited state 497nm = 1s 2 4s 1 to 1s 2 2p 1 497nm = 1s 2 4s 1 to 1s 2 2p 1 Excited state to lower excited state 460nm = 1s 2 4d 1 to 1s 2 2p 1 460nm = 1s 2 4d 1 to 1s 2 2p 1 Excited state to lower excited state

Practice What is the energy of a photon emitted from a hydrogen atom when an electron jumps from n = 3 to n = 1? What is the energy of a photon emitted from a hydrogen atom when an electron jumps from n = 3 to n = 1?

Test Review Problem In graphite, carbon atoms are about 142pm apart. This distance could be resolved by a system that emitted a wavelength of light roughly half of that distance. What is the frequency and energy of this light? In graphite, carbon atoms are about 142pm apart. This distance could be resolved by a system that emitted a wavelength of light roughly half of that distance. What is the frequency and energy of this light?

Test Review Problem Chlorofluorocarbons, or CFC’s, have been banned from production in the US since When they are released into the air, they may migrate into the upper atmosphere. In the upper atmosphere, the carbon- chlorine bonds can be broken by a photon of light with energy of 5.45x J. The free chlorine atom can go on to cause the decomposition of multiple ozone molecules in a catalytic process (and therefore why they are banned). What is the wavelength of light that can cause the bond to break? Chlorofluorocarbons, or CFC’s, have been banned from production in the US since When they are released into the air, they may migrate into the upper atmosphere. In the upper atmosphere, the carbon- chlorine bonds can be broken by a photon of light with energy of 5.45x J. The free chlorine atom can go on to cause the decomposition of multiple ozone molecules in a catalytic process (and therefore why they are banned). What is the wavelength of light that can cause the bond to break?

Old cordless phones used a 700.0MHz band for communication with the base station. What is the wavelength and energy of a photon of this light? Old cordless phones used a 700.0MHz band for communication with the base station. What is the wavelength and energy of a photon of this light?