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# Electromagnetic Radiation and Energy - PowerPoint PPT Presentation

Electromagnetic Radiation and Energy. Electromagnetic Radiation: Energy traveling through space Three Characteristics of Waves: Wavelength : (symbolized l) Distance between two consecutive peaks or troughs in a wave Frequency : (symbolized n) How many waves pass a given point per second

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Presentation Transcript
• Energy traveling through space

Three Characteristics of Waves:

• Wavelength: (symbolized l)
• Distance between two consecutive peaks or troughs in a wave
• Frequency: (symbolized n)
• How many waves pass a given point per second
• Speed: (symbolized c)
• How fast a given peak moves through space

c = λ x ν

c = speed of light = 2.9979 x 108 m/s

ν = frequency (s-1 or Hz)

λ = wavelength (m)

Spectra
• Sunlight yields continuous spectrum
• Energized gaseous elements yield certain wavelengths
• Line emission spectrum
Rydberg
• Why did gaseous atoms emit certain wavelengths?
• Didn’t find out why, but came up with an equation
• Rydberg equation
• N=3, red line
• N=4, green line
• N=5, blue line
• Lyman series
• n > 1 to n = 1
• UV (invisible)
• Balmer series
• n > 2 to n = 2
• Visible wavelengths
The Bohr Model of the Atom
• Explained Rydberg
• Electron energy quantized
• Electron only occupies certain energy levels or orbitals
• If it didn’t, electron would crash into protons in nucleus
• As “n” increases energy becomes less negative
• Increases
• Only certain amts of E may be absorbed/emitted
• If electron in lowest possible energy level
• Ground state
• If electron in excited energy level
• Excited state
• One can calculate energy needed to raise H electron per atom from ground state (n=1) to first excited state (n=2)
Bohr’s Model
• Explains emission spectrum of H
• Movement of electrons from one quantized energy level to a lower one gave distinct emission wavelengths
• Model only good for one electron system
Atomic orbital

The probability function that defines the distribution of electron density in space around the atomic nucleus.

The s-orbital
• The simplest orbital
• The only orbital in the s-subshell
• Occurs in every principal energy level
• “s” stands for “sharp”
• The first energy level only houses this orbital
• Can house up to 2 electrons
The p-orbitals
• Start in second principle energy level (n=2)
• There are three p-orbitals in the p-subshell (see below)
• And one s-orbital
• “p” stands for “principle”
• Can house up to 6 electrons
• Has one nodal surface
• Nodal plane = a planar surface in which there’s zero probability of find an electron

2px 2py 2pz

The d-orbitals
• Start in third principle energy level (n=3)
• There are five d-orbitals in the d-subshell
• And one s-orbital
• And three p-orbitals
• Can house up to 10 electrons
• “d” stands for “diffuse”
• Has two nodal surfaces

3dyz 3dxz 3dxy 3dx2-y2 3dz2

The f-orbitals
• Start in fourth principle energy level (n=4)
• There are seven f-orbitals in the f-subshell
• And one s-orbital
• And three p-orbitals
• And five d-orbitals
• Can house up to 14 electrons
• “f” stands for “fundamental”
• Has 3 nodal surfaces
Electron configuration
• Electron must be identified as to where it is located
• Hydrogen:
• One electron in first energy level and s-subshell
• Thus, 1s1 (= Aufbau electron configuration)
• 1 states energy level (n)
• s designates subshell
• Superscript 1 tells how many electrons are in the s-subshell
• Can also use orbital box or line diagrams
• Let’s take a look
Pauli Exclusion Principle
• An atomic orbital holds a maximum of two electrons
• Both electrons must have opposite spins
• ms = +1/2 & -1/2
Hund’s Rule
• Electron configuration most stable with electrons in half-filled orbitals before coupling
Exercises
• Give me the Aufbau electron configurations for:
• Y
• Te
• Hf
• Tl
• 112
Sundry matters pertaining to d-block metals
• Stability is increased when:
• d-subshell is half-filled (d5)
• d-subshell is completely filled (d10)
• Electrons will be taken from the s-subshell to fill the d-subshell
• But there is a limit
• No more than 2 electrons taken from s-subshell
• Given the above, which subshell electrons will d-block metals lose first when they ionize?
• So what are the correct electron configurations of Cr and Ag?
• Caveat
• Not all metals follow the above; i.e., take from s-subshell and give to d-subshell
• Ni & Pt, for example
Sundry matters pertaining to f-block metals
• Stability is increased when:
• f-subshell is half-filled (f7)
• f-subshell is completely filled (f14)
• Electron will be taken from the d-subshell to fill the f-subshell
• Eu & Yb
• Am & No