Chapter 4 Electron Configurations

Early thoughtsMuch understanding of electron behavior comes from studies of how light interacts with matter.Early belief was that light traveled as a wave, but some experiments showed behavior to be as a stream of tiny fast moving particles

Waves Today scientists recognize light has properties of waves and particlesWaves: light is electromagnetic radiation and travels in electromagnetic waves.

4 Characteristics of a wave:1) amplitude - height of the wave. For light it is the brightness2) Wavelength () distance from crest to crest. For light defines the type of light Visible light range 400-750nm

Properties continued3) Frequency () measures how fast the wave oscillates up and down. It is measured in number per second. Hertz = 1 cycle per secondFM radio = 93.1 MHz or 93.1 x 106 cycles per secondVisible light = 4 x 1014 cycles per second to 7 x 1014 cycles per second 4) speed 3.00 x 108 m/s

Short wavelength, high frequencyLong wavelength, low frequencyVisible SpectrumROY G BIV Longer wavelength shorter wavelength

Electromagnetic spectrum (meters)10-11 gamma10-9 x-rays10-8 UV10-7 visible light10-6 infrared10-2 microwave1 TV

Wavelength and frequencyWavelength and frequency are inversely related!! = c/Where is the wavelength, c is the speed of light and is the frequencySpeed of light = Constant = 3.00 x 108m/sec

ExampleExample: An infrared light has a wavelength of 2.42 x 10-6m. Calculate the frequency of this light. = c/ = 3.0 x 108m/sec = 2.42 x 10-6m= 1.2 x 1014 waves/sec

Wavelength and frequency****Remember and are inverse. Therefore short wavelength = high frequency!!

Quantum TheoryNeeded to explain why certain elements when heated give off a characteristic light (certain color)1900- Max Planck idea of quantum

Quantum Theory- The amount of energy (electromagnetic radiation) an object absorbs/emits occurs only in fixed amounts called quanta (quantum)- Quanta finite amount of energy that can be gained or lost by an atom.

1905 Einsteins theoryEinstein explained photoelectric effect by proposing that light consists of quanta of energy called PHOTONS Photon = discrete bit of energy Consider light traveling as photons

Energy equationAmount of energy of a photon described asE = hWhere E = energy = frequencyh = Plancks constant = 6.6262 x 10-34 J sJoule = SI unit for energy

Photoelectric effect electrons are ejected from the surface of a metal when light shines on the metal. The frequency determines the amount of energy. The higher the frequency, the more energy per photon.

Photoelectric effectEx. X-rays have a high frequency; therefore can damage organisms while radio waves have a low frequency.

Dual nature of radiant energy Photons act both like particles and waves.Line Spectra: A spectrum that contains only certain colors, or wavelengths

Question: How are electrons arranged in atoms?

Note: All elements emit light when they are vaporized in an intense flame or when electricity is passed through their gaseous state.

How are electrons arranged in atoms?Explanation: Bohr atom: 1911postulated that atoms have energy levels in which the electrons orbitenergy levels and/or orbits are labeled by a quantum number, n. lowest energy level = ground state n=1

How are electrons arranged in atoms?when an electron absorbs energy, it jumps to a higher level (known as the excited state) n = 2,3 or 4Bohr model of an atom Hydrogen Red- e falls from 3 to 2Blue e falls from 4 to 2Violet e falls from 6 to 2

1924 Louis DeBroglie If waves of light can act as a particle, then particles of matter should act like a wave. Found to be true.

DeBroglieMatter waves = wavelike behavior of particles.From equation wave nature is inversely related to mass therefore we dont notice wave nature of large objects. However, electrons have a small mass so they have a larger wave characteristic

Schroedingers wave equationpredicted probability of finding an electron in the electron cloud around nucleus. Gave us four quantum numbers to describe the position.

Heisenbergs Uncertainty PrincipleThe position and momentum of a moving object cannot simultaneously be measured and known exactly.Cannot know where it is and where its going at the same time.

Quantum mechanical model of an atom Treats the electrons as a wave that has quantized its energyDescribes the probability that electrons will be found in certain locations around the nucleus.

OrbitalsOrbitals atomic orbital is a region around the nucleus of an atom where an electron with a given energy is likely to be found (high probability)Have characteristic shapes, sizes and energies.Four different kinds of orbitals s, p, d, f.

S and p orbitals

Orbitals and energy

Principal Energy Level = quantum number n. Principal Quantum number Value of n = 1,2,3,4,5,6,7Tells you the distance from the nucleus

sublevelsEach level is divided into sublevels# of sublevels = value of nN=1 1 subleveln=2 2 sublevels s,p,d or f shows the shape

Orbital shapeEach sublevel has a certain number of orbitals which are directed three dimensionally S = 1 sphereP = 3 figure 8 (along the x,y or z axis)D = 5 figure 4-27 p. 145F = 7

Each electron in an orbital will have a spin 2 options clockwise, vs. counter clockwise.Electron configurationPauli Exclusion Principle each orbital in an atom can hold at most 2 electrons and their electrons must have opposite spin.

Aufbau Principle- electrons are added one at a time to the lowest energy orbitals availableHunds Rule electrons occupy equal energy orbitals so that the maximum number or unpaired electrons result. Occupy singly before pairing

Diagonal Rule: for order of sublevels: must remember 1s, 2s, 2p, 3s, 3p, 4sExceptions to Aufbau PrincipleCr Z=24 Cu Z = 29

Energy levelsNumber of electrons per energy level1st = 22nd = 83rd = 184th = 32

Number of electrons per orbital2Difference between paired and unpaired electronsPaired = 2 electrons in the same orbitalUnpaired = 1 electron in the orbital