WavesWhat do light waves have to do with chemistry?

The Big Idea!The atoms of each element have a unique arrangement of electrons

Light and Quantized EnergyLight, a form of electromagnetic radiation, has characteristics of both a wave and a particle

Electromagnetic RadiationLight is just one form of electromagnetic radiationElectromagnetic radiation travels in the form of wavesAll waves have amplitude, wavelength, frequency and speed

Electromagnetic Spectrum

US Frequency Allocations

WavelengthSymbol is Defined as the distance between two crests or two troughs

Speed of LightIs it really a constant?It equals 3.00 x 108 m/sSymbol is c

The speed of light (3.00 108 m/s) is the product of its wavelength and frequency c = .Speed of Light

FrequencyIts symbol is The number of wave cycles that pass a given point in one secondMeasured in hertz (Hz) (cycles/sec)C =

Frequency vs WavelengthLong wavelengths have low frequenciesShort wavelengths have high frequencies

Who is Max Planck and why do we care?The year is 1895Physicists are trying to model the EM radiation of a black body A black body absorbs all light and emits it as black body radiationMax is working hard to model this

1895 Viola!!Success!Devised Plancks constant: Equantum= hE = amount of energyh = Plancks constant:6.6262 x 10-34 J s (J = joule)

What does this mean?Matter can emit or absorb energy only in whole-number multiples of h : 1 h, 2 h, etc.

1905 Einstein comes on the scenePublishes a paper on light quanta (Won Nobel Prize for this in 1921)Explained photoelectric effect using this particle based modelProved Plancks model correctMillikan Tried to disprove both Planck and Einstein for 10 years

Einsteins explanation of his theoryAccording to the assumption considered here, in the propagation of a light ray emitted from a point source, the energy is not distributed continuously over ever-increasing volumes of space, but consists of a finite number of energy quanta localized at points of space that move without dividing, and can be absorbed or generated only as complete units.

1920s - Louis de BroglieScientist who used Plancks constant to predict that electrons could act like waves, since waves could act like particlesThis principle is used in electron microscopes, where electrons streams are diffracted the same way light waves are diffracted by lenses

A picture taken with an electon scanningmicroscope

PhotonsParticles of light are called photonsEach photon carries with it a specific value of energy based on its frequencyHigh frequency photons carry large amounts of energy

Atomic Emission SpectraLight in a neon sign is produced when electricity is passed through a tube filled with neon gas and excites the neon atoms.The excited atoms emit light to release energy.When the light passes through a slit and then a prism, a line spectrum is formed.

Line Spectra

Atomic Emission SpectraA line spectrum is also called an atomic emission spectrumIts formed by the energy given off, in the form of light, when an electron moves from its excited state to its ground stateOrigin of Spectral Lines

Atomic Emission SpectraThe atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element when it is excited.Each elements atomic emission spectrum is unique.

Photograph of a linespectrum from helium

Several examplesof line spectra

Quantum Theory and the AtomWavelike properties of electrons help relate atomic emission spectra, energy states of atoms, and atomic orbitals

Bohrs Model of the AtomBohr suggested that an electron moves around the nucleus only in certain allowed circular orbits.

Bohrs Model of the AtomWhen an electron drops from a higher energy orbit to a lower-energy orbit, a photon is emitted.

Electrons are WeirdHeisenberg Uncertainty Principle: It is impossible to know both the location and velocity of an electron at the same timeAn electron can only be located when a photon strikes it. The collision causes it to change direction and velocity.

Heisenberg Uncertainty Principle

How are electrons arranged around an atom?Bohr determined that electrons gained or lost energy in quanta, or specific amounts. These he labeled as quantum numbers, or n.The n numbers refer to the energy levels, which are the same as the period numbers on the periodic table.

What are sublevels?Each energy level is divided into sublevelsThere are four different sublevels: s, p, d and f

Probability and OrbitalsOrbital: region around the nucleus where an electron is likely to be foundHave characteristic shapes, sizes and energiesEach can only hold 2 electrons with opposite spins

How do orbitals relate to energy?Each principle energy level is divided into sublevels: s,p,d,fEach sublevel has an odd number of orbitals: s has 1, p has 3, d has 5, and f has 7

What do the orbitals look like?Orbital in the s sublevelOrbitals in the p sublevel

Each one of these orbitals holds only two electrons. The d sublevel holds 10 electrons total, and the fsublevel holds 14 electrons total.

Orbitals in the d sublevelOrbitals in the f sublevel

Orbitals

Energy sublevels are contained within the principal energy levels.Energy levels can be thought of as rows of seats in a theater. The rows that are higher up and farther from the stage contain more seats.

David's Whizzy Periodic Table

Energy LevelSublevelsOrbitals# of Electrons1s122sp13263spd13526104spdf1357261014

Electron ConfigurationA set of three rules can be used to determine electron arrangement in an atom

What is electron configuration?Each electron has a characteristic energy and a characteristic spinEach electron is located in a specific orbital with a specific quantum number; this is called its electron configurationThere are three rules to use to determine where each electron is located and what spin it has

What are the rules for assigning configurations?Aufbau Principle: electrons are added to an atom one at a time starting with the lowest energy orbital 1s will get the first 2 electrons (lowest energy)2s will get the second 2 electrons (next higher energy)2p will get the next 6 electrons (next higher energy)

What are some examples?Hydrogen: has 1 electronFrom the Periodic Table, it is in row 1, so n = 1It has a 1s orbitalIts configuration is 1s1

Another exampleHelium has 2 electronsAccording to the P. Table, it is in the 1st row, so n = 1It has an s orbitalIts configuration is 1s2

Another exampleLithium has 3 electronsThe first two electrons are the same as in He, so the first term is 1s2It is in the 2nd row, so n=2Its configuration is 1s2 2s1

What is sublevel notation?The type of electron configuration we have just done is also called sublevel notationThe order in which the levels fill is shown on the next slide and on your handout

You can tell which sublevel theelectrons of an element are inby looking at the elements location in thePeriodic Table.S = pinkp = blued = greenf = yellow

What is the next rule for assigning configurations?Pauli Exclusion Principle: Each orbital can hold up to two electrons; must have opposite spinsHunds Rule: When electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with spins that are parallel

What are electron spins?Electrons have their own spins, represented by up and down arrowsThey can spin clockwise or counterclockwiseEach ortibal holds two electrons, and they have to be spinning in opposite directions

How do I represent this?Electron spins and the order in which they fill orbitals can be represented using an orbital diagramOrbital diagrams use arrows and lines or squares to represent electrons in their orbitals

What are some examples?What is the orbital diagram for boron?Its electron configuration is 1s22s22p1Its orbital diagram is1s2s2pOrbital DiagramsElectronic Configuration

The aufbau principle states that each electron occupies the lowest energy orbital available.

What are valence electrons?Electrons in the outermost energy level (the n #)Can be determined by counting the number of s- and p-electrons since the most recent noble gas These electrons are primarily responsible for the reactivities of the elements in the s- and p-sections of the Periodic Table

What are some examples?How many valence electrons does chlorine have?How many valence electrons does sodium have?How many valence electrons does aluminum have?

*