Chapter 6 Part 1 Structure of the atom What IS the structure of an atom? What are the properties of atoms? REMEMBER: structure affects function! Important questions: Where are the electrons? What is the energy of an electron? Chapter 6 Part 1 Dual Nature of Light λν=c E = hν Line Spectrum Bohr Model of Hydrogen Atom Mary J. Bojan Chem 110 1
Why do we start with Chapter 6? Overview of Chem 110 Key themes: structure effects function (properties). How do we know about atoms, etc.? Structure of atom Ch. 6 Properties of Atom Ch. 7 How atoms bond to form molecules Ch. 8 Structure of molecules Ch. 9 Properties of molecules Ch. 10, 11, 13 Molecules REACT! Ch. 3, 4, 10 Rules that govern reactions Thermodynamics (think energy) Ch. 5 Equilibrium Ch. 15 Mary J. Bojan Chem 110 2
What is the structure of an ATOM? COMPONENTS OF ATOMS proton p electron e neutron n mass (a.m.u.) charge (a.u.) Neutral Ion 19 F 9 39 K 19 + Mary J. Bojan Chem 110 3
ISOTOPES Isotopes: atomic number =??? DEFINES identity of element For a given element, number of protons is fixed, but number of neutrons can vary. 35 Cl 37 Cl 17 17 Mary J. Bojan Chem 110 4
We define: The Atomic Mass Scale mass of 12 C = exactly 12 amu. Use ISOTOPE RATIOS to find Average Atomic Masses Mary J. Bojan Chem 110 5
Another definition: The Atomic Mass Scale Problem: no one can see (or weigh) an atom 1 mole of 12 C has a mass of 12 g What is a mole? 1 mole of anything (atoms, molecules, green peas) = Avogadro s number of them How BIG is a mole? Mary J. Bojan Chem 110 6
The Mole and Avogadro s Number Mole: connection between microscopic (what we don t see: atoms) and macroscopic (what we see) Mary J. Bojan Chem 110 7
Back to the atom Mary J. Bojan Chem 110 8
Structure of Atom ~1910 Earnest Rutherford tested Thompson s plum pudding Model Rutherford concludes: massive nucleus with electrons orbiting around it. Mary J. Bojan Chem 110 9
Modern View of atom An atom is almost entirely empty space. 1nm = 10-9 m 10Å = 1nm Å= angstrom Atom Diameter = 0.1-0.5 nm Nuclear diameter = 10-5 nm Atom diameter = 10,000 x nuclear diameter Mary J. Bojan Chem 110 10
study of light interacting with matter WHAT IS LIGHT???? Mary J. Bojan Chem 110 11
Electromagnetic radiation What KIND of energy? kinetic or potential What is moving? What are the units of energy????? Mary J. Bojan Chem 110 12
Electromagnetic radiation (light) Light behaves as a wave! c = 3.00x10 +8 m/s for light λ = wavelength ν = frequency c = λν Mary J. Bojan Chem 110 13
Electromagnetic radiation What is the range (wavelengths) of visible light? Does uv light have longer or shorter λ than visible? Rank the following ranges of light in order of increasing λ. uv, ir, visible, microwave What is the frequency of light if λ = 450nm? c = λν c = 3.00x10 +8 m/s for light What has a higher frequency? a) visible light (λ = 640nm) b) microwaves (λ = 600cm) Mary J. Bojan Chem 110 14
Electromagnetic Spectrum Regions of EM spectrum gamma X-Ray ultraviolet visible infrared microwave radio Common use? Dangerous or not??? Mary J. Bojan Chem 110 15
Light behaves as a wave! Or does it??? Several phenomena were inconsistent with the wave nature of light. Blackbody radiation Photoelectric effect Line spectrum of atoms Black body radiation Planck shows: E= nhν n = integer ν = frequency of emitted light h = Planck s constant = 6.626 10 34 J-s Energy = hν photon energy frequency of photon Mary J. Bojan Chem 110 16
Photon energy What is the energy of a green photon (wavelength equal to 523 nm)? 1. 5.74 10 +14 J 2. 3.80 10 19 J 3. 5.23 10 29 J 4. 1.90 10 19 J 5. 3.80 10 28 J Mary J. Bojan Chem 110 17
Spectroscopy: light interacting with matter λ Energy Interaction with matter gamma X-Ray ultraviolet visible infrared microwave radio Mary J. Bojan Chem 110 18
Is light emitted or absorbed? How do I know? We need a brief excursion into Chapter 5 Mary J. Bojan Chem 110 19
First Law of Thermodynamics Energy can be converted from one form to another, but the total energy Law of conservation of energy all energy lost by a system under observation must be gained by the surroundings (and vice versa) *during energy conversion, some heat is always produced" Mary J. Bojan Chem 110 20
Internal Energy Internal energy: total energy (E) associated with a system; the sum of all sources of kinetic & potential energy. " The capacity to do work or transfer heat.! Quantitative definition:" ΔE = E final E initial " ΔE = q + w" Mary J. Bojan Chem 110 21
Which has more energy? E is a state function (path independent)" Mary J. Bojan Chem 110 22
Exothermic and Endothermic ENTHALPY: Heat transferred when P is constant ΔH (=q p ) Usually run chemical reactions at constant pressure (atmospheric). Exothermic: heat System Surroundings ΔH = Endothermic heat Surroundings System ΔH = + Mary J. Bojan Chem 110 23
What you need to know from Chapter 5 Difference between kinetic and potential energy (can you make up your own examples?) Know units of energy and order of magnitude of different kinds of energies (photon energy, etc.) Be watching for electronic energy, i.e., the energy of an electron. What is the First Law of Thermodynamics? Watch for how the potential energy of electrons gets converted to kinetic energy (a photon). What is meant by the system? The surroundings? What does the sign of energy mean? + means energy into the system (endothermic) means energy out of the system (exothermic) Notice State functions (like P, T V) as we encounter them and keep the definition of state function in mind. Why is it useful to know that these are state functions? Remember that Enthalpy is another word for heat: specifically it is an heat measured when the system is at constant pressure, but for now, just know that it is a form of energy (heat). Mary J. Bojan Chem 110 24