14 November 2011  Objective: You will be able to:  describe evidence for the current theory of the electronic structure of atoms.  Homework: p. 312 #3, 4, 5, 6, 7, 9, 16, 19, 25, 32

Electronic Structure of Atoms

Next Units:  Electron configuration  Trends on the periodic table  Ionic/covalent bonding  Chemical reactivity

In order to understand these things  we’ll study the electronic structure of atoms

The Wave Nature of Light  electromagnetic radiation (a.k.a. light) is a form of energy with wave and particle characteristics. It moves through a vacuum at the speed of light  speed of light: 3.00x10 8 m/s

To describe waves…  wavelength ( λ lamda): the distance between two adjacent peaks of a wave  frequency ( v ): the number of wavelengths that pass a given point in a second

Electromagnetic Spectrum

 electromagnetic spectrum includes all wavelengths of radiant energy  visible spectrum: the part of the electromagnetic spectrum that is visible to the human eye (wavelengths between 400 and 700 nm)

Quantized Energy and Photons  quantum (a.k.a. photon) is a specific particle of light energy that can be emitted or absorbed as electromagnetic radiation.  Energy of a photon E=hv  Energy is quantized – matter is allowed to emit or absorb energy in discrete amounts, whole number multiples of hv.

How are these things related to electromagnetic radiation? v=c/λE=hv λ = wavelength in nm v = frequency in 1/s or hertz 1 Hz = 1/s E = energy of a single photon in Joules c = speed of light = 3.00x10 8 m/s = 3.00x10 17 nm/s 1 nm = m h = Planck’s constant = 6.63x J s E=hc/λ

Example 1 Calculate the energy (in joules) of a. a photon with a wavelength of 5.00x10 4 nm (infrared region) b. a photon with a wavelength of 5.00x10 -2 nm (x-ray region)

Example 2  What is the frequency and the energy of a single photon?  What is the energy of a mole of photons of light having a wavelength of 555 nm?

Problem  The energy of a photon is 5.87x J. What is its wavelength, in nanometers?

Homework  p. 312 #3, 4, 5, 6, 7, 9, 16, 19, 25, 32

15 November 2011  Take Out Homework  Objective: You will be able to:  describe and explain experimental evidence for energy levels  Homework Quiz: The energy of a photon is 3.98x J. What color light do you observe?

Agenda I. Homework Quiz II. Hand back tests III. Line spectra and the Bohr model of the atom Homework: p. 313 #23, 24, 25, 26, 30, 31, 35, 36

Line Spectra and the Bohr Model  atomic emission spectrum (a.k.a. line spectrum): a pattern of discrete lines of different wavelengths that result when the light energy emitted from energized atoms is passed through a prism  Each element produces a characteristic or identifiable pattern

Demo  Emission spectra of common cations  Note: we don’t have a way to separate all the wavelengths of light into discrete lines of color, so we’re just seeing all those lines of color blended together.  Chr_Bw&feature=related Chr_Bw&feature=related

So, why do we see these discrete lines of color?  Bohr model of the atom: energies are quantized. Electrons move in circular, fixed energy orbits around the nucleus.  Usually, electrons are in the most stable “ground” state.  When energy (a photon) is added, they “jump” up to the “excited” state  They fall back down, and release that photon.

Multimedia  S1Ro-sc S1Ro-sc  quantumzone/lines2.html quantumzone/lines2.html

Homework  p. 313 #23, 24, 25, 26, 30, 31, 35, 36

16 November 2011  Objective: You will be able to:  explain how line spectra give evidence for the existence of energy levels  explain how quantum mechanics describes electron configuration

Agenda I. Homework Quiz II. Go over homework III. How do atoms emit photons? IV. Quantum mechanics: how do we describe where the electrons are?! V. Writing orbital notation and electron configuration Homework: p. 313 #23-26, 30, 35, 48, 53, 60, 63,

Energy levels

Wave Behavior of Matter  Like light, electrons have characteristics of both waves and particles. Because a wave extends into space, its location is not precisely defined.  uncertainty principle: it is impossible to simultaneously determine the exact position and momentum of an electron.  we can only determine the probability of finding an electron in a certain region of space.

Quantum Mechanics and Atomic Orbitals  quantum mechanical model: mathematical model that incorporates both the wave and particle characteristics of electrons in atoms.  quantum numbers: describe properties of electrons and orbitals  each electron has a series of four quantum numbers

Table of Quantum Numbers

Table of quantum numbers and orbital designations

Pauli Exclusion Principle  Two electrons in an atom can’t have the same four quantum numbers  Two electrons per orbital, with opposite spins

Representations of Orbitals  orbital: calculated probability of finding an electron of a given energy in a region of space

p orbitals

d orbitals

 orbital ≠ orbit

17 November 2011  Objective: You will be able to:  write the orbital and electron configuration for any element  describe several exceptions to the orbital filling rules  Homework Quiz: Describe, as completely as you can in a paragraph or two, the evidence that convinced Neils Bohr of the existence of energy levels instead of a cloud of electrons.

Agenda I. Homework Quiz II. Go over homework III. Electron configuration notation IV. Problem Set Unit 4 Quiz Weds.

Atoms with more than one electron  like hydrogen  electron-electron repulsions cause different sublevels to have different energies

Order those orbitals fill

Electron Configuration  distribution of electrons among various orbitals of an atom

Rules for Writing E- Config.  at the ground state 1. Fill the lowest energy level first. Electrons in the same orbital must have opposite spins. Total number of electrons = atomic number 2. Only two electrons per orbital! 3. Do not pair electrons in a orbitals of the same energy until each orbital has one electron of the same spin (Hund’s rule) 4. Label each sublevel with the energy level number and letter of the sublevel

Examples 1. phosphorus 2. calcium 3. iron

Paired-ness of Electrons  Paramagnetic: an atom having one or more unpaired electrons  Ex: Li, B, C…  Diamagnetic: all electrons in an atom are paired.  Ex:

Excited-State Configuration  has a higher energy than the ground-state electron configuration.  One or more electrons occupy higher energy levels than predicted by the rules  Ex: Iron in an excited state:

Electron Configuration and the Periodic Table  Elements with similar electron configurations arranged in columns

Examples 1. Write the electron configuration for palladium 2. Write the electron configuration for osmium

Condensed Electron Config.  shows only the electrons occupying the outermost sublevels  preceded by the symbol for the noble gas in the row above the element  Example: calcium  Example: iodine

Unusual Electron Configs.  Cr and Mo: ground state valence electrons are arranged s 1 d 5 rather than s 2 d 4  a half filled d orbital is more stable than a more-than-half-filled d orbital  Cu, Ag and Au have s 1 d 10 ground state configs because of the stability of a fill d orbital

21 November 2011  Objective: You will be able to:  describe the electronic structure of an atom and make associated calculations.

Agenda I. Math with exponents (#6) II. Problem set work time Homework: Problem set due tomorrow Quiz Mon. on all electronic structure, calculations, evidence for Bohr’s theory…

28 November 2011  Objective: You will be able to:  show what you know about the electronic structure of atoms on a quiz  You need:  periodic table  calculator  pen/pencil

You have only one period  Work smart: Go through the MC and answer the ones you can easily answer.  Then, go through and spend more time on the difficult ones.  Only write the noble gas notation if you need electron configuration to answer a question.  Only do the orbital notation of the parts you really need to “see.”  Don’t spend a long time on any one question until you’ve tried every problem on the quiz.  Pay attention to UNITS.