Chapter 5 - Electron Structure According to the Bohr Model, electrons (e-) can only orbit the nucleus in specific, allowed pathways. They move toward and away from the nucleus by “steps” or discrete amounts of energy that are released or absorbed. e- farther from the nucleus have more energy. Those closer to the nucleus have less energy. Very similar to a ladder. Just as you cannot step on the air between the rungs, an electron cannot exist between the levels.

Ground state: the lowest energy of an atom Excited state: higher potential energy state Energy absorbed  e- moves to higher state Energy emitted  e- moves to lower state Higher excited state Excited state Ground state Excited state Ground state Energy Energy

The Duality of Light Light as a Wave Two - faced “Duality” means that there are two ways to represent light. Light can behave like a wave or like a particle. Wave Particle Light as a Wave Wavelength (λ – “lambda”): the distance between the peaks Frequency (ν – “nu”): number of waves that pass a given point in a specific amount of time λ

wavelength (λ) frequency (ν) c = 3.00 x 108 m/sec The speed of light (c) is constant. So as one gets bigger…the other has to get smaller! Because of this relationship: Longer wavelength → Lower frequency Shorter wavelength → Higher frequency In the visible spectrum, color is associated with different wavelengths (ROY G. BIV) Longer λ and lower ν : towards Red Shorter λ and higher ν : towards Violet The relationship is: c = λ ν Examples…students walking across front of room Marching Band turning a corner

c = 3.00 x 108 m/sec c = λ ν Each of the different areas along the electromagnetic spectrum follows this equation The marching band example

ν is the frequency of the light, and There is obviously a relationship between the frequency of light and its energy: Ephoton = hν ν is the frequency of the light, and h = 6.626 x 10-34 J·s (Planck’s constant) Higher ν → Higher E (Violet) Lower ν → Lower E (Red) Spectroscopy – gives you information about the structure of the atom…in other words it tells you the ladder the electrons follow Like fingerprints to the atom…identifies the element Hydrogen’s Line Emission Spectrum Excited State Ground State Energy (Light) Turn this sideways and it looks like a ladder Go back to previous slide…show only certain wavelengths make it through due to the ladder of energy levels

Specific element gas (light) …shows only the electrons specific energy levels …it’s ladder White light …would show the whole visible spectrum …not just the ladder …Look back two slides

Light as a Particle Photoelectric Effect: e- are emitted from a metal when light of a high enough frequency shines on the metal. Importance: e- were not emitted when a light’s frequency was below a certain point – regardless of how long the light was shone on the metal => Light as a Particle Quantum – a small bundle of energy Photon – a small bundle of energy of light with zero mass Light Electrons Metal

A Little Bit of History...again! Modern Atomic Theory A Little Bit of History...again! We know electrons (e-) are particles, but in 1924, French scientist Louis de Broglie propose that e- have a wave nature as well (investigation showed this to be true) In 1926, Erwin Schrödinger developed a wave equation for e- that described their energy values correctly : Eψ(x) = [-(h2/8π2m)d2/dx2 + V(x)] ψ(x) (OUCH!!!! Don’t worry, you don’t need to know this equation!!!) In 1927, Werner Heisenberg developed his Uncertainty Principle – it is impossible to determine simultaneously both the position and velocity of an electron or any other particle This all led to the modern quantum theory

Modern Atomic Theory Orbitals describe the three dimensional space that electrons occupy. The location of an electron can only be described by probability. (ex. You in this classroom and your parents are looking for you.) Orbitals give shape to the atom. These properties allow us to describe electrons in terms of their energy and position. Ahhh Yes….. Quantum Mechanics! Orbital Not an Orbit

Quantum Mechanics….Sounds Scary!!!! Think of it this way… It is the “address” of an electron Did you ever mail a letter? Where do you live? (4 things) State City Street Name House Number Electrons are identified the same way (4 things)… Principle (identified by n) Orbital (identified by l) Magnetic (identified by ml) Spin (identified by ms) Kevin Lockard 2528 South St. Lansdale, PA 19446

Four Quantum Numbers 1. Principle Quantum Number (n) Indicates the main energy level occupied by the e- (distance from the nucleus) Shell Number (1st shell is closest to nucleus, 2nd is further, and so on …) Values of n can only be positive integers (1, 2, 3, etc.) 2. Orbital Quantum Number Indicates the shape of the orbital (actual 3D space where the probability of finding e- is greatest) Sublevel of n Designated s, p, d, f 1 2 3 s d p

s orbital Spherical shaped One orbital Holds two e- p orbital Peanut or dumbbell shaped Three orbitals Holds six e- d orbital Double peanut shaped Five orbitals Holds ten e- f orbital Flower shaped Seven orbitals Holds fourteen e-

3. Magnetic Quantum Number Indicates the orientation of an orbital (the plane that the orbital is in) p orbitals can have three different orientations, one along the x-axis, one along the y-axis, and one along the z-axis 4. Spin Quantum Number Indicates the two spin states of an e- in an orbital (only 2 e- in each orbital, and they spin in opposite directions) Represented by arrows px py pz Empty Half-Filled Filled

How do you write this address for the electron? …2 different ways… Electron Configurations – Quick address Like you were giving your address out to a friend These have numbers and letters) It will look like this…. 1s22s22p63s23p63d10 etc….. 4 Quantum Numbers – Boxed Address

How do you write this address for the electron? …2 different ways… There are a few rules that help us represent the arrangement of electrons in atoms address (tells us the “route” the mailman takes) Aufbau (“building up”) principle: an electron occupies the lowest energy possible Hund’s rule: orbitals of equal energy are each occupied by one electron before accepting a second electron Pauli exclusion principle: no two electrons in the same atom will have the same set of quantum numbers (no two fans have the same seat) e-

What’s the route the “mailman” takes?

What’s the route the “mailman” takes?

s p d f Example Sulfur = 1s22s22p63s23p4 Electron Configurations – Quick address To write electron configurations, you need to know: Period # 1 – 7 (exception for d orbitals – 1 less) Subshell letter (e.g. s, p, d, f…) Atomic # is # of e- as an exponent s p d f Example Sulfur = 1s22s22p63s23p4