1. Light

2. The Nature of Light  Visible light is one type of electromagnetic radiation (EM).  Other types include: x-rays, microwaves, and radiowaves  Light has dual nature  Wave (moves through space as a wave) and particle (has energy)

3. Wave Nature of Light  When thinking of light as a wave we must consider:  Frequency ( ν, Greek nu) = how fast the wave moves up and down per second (s -1, also Hz (hertz))  Wavelength ( λ, Greek lambda) = distance between waves; expressed in meters (m)

4. How fast does a wave move?  Depends on frequency ( ν ) and wavelength ( λ )  In a vacuum waves travel at 3.0 x 10 8 m/s  This is called the speed of light (c)  c = ν x λ

5. Particle Nature of Light  We need a little help from  Einstein showed that different colors of light have different amounts of energy and it takes a certain amount of energy for e- to be emitted.

6. How to calculate the energy  Well here’s the formula:  E (energy) = h (planck’s constant) x ν (frequency)

7. Rutherford’s Model  How do we picture an atom? The nuclear model  Mimicks solar system: “sun” = nucleus “planets” = electrons

8. Uh-Oh! Rutherford…we have a problem!  The e - moves in a circular path, is constantly accelerating, constantly changing direction, radiates energy, orbit decays, and then SMASH (into the nucleus)!!!  Rutherford’s atom should collapse instantly. 

9. So, how do we make sense of it all?  Lets take a look at atoms with light.  When you look through a prism or diffraction grating, you see a rainbow that is continuous (no breaks in color)  When you look through a diffraction grating at a light given off by energized atoms, you see a discontinuous spectrum (breaks in color)

10. Bright-Line Emission Spectrum  Each element has a unique…  emission spectrum; the simplest is hydrogen.  Each element and compound have a unique absorption pattern, too.

11. Bohr atom  Niels Bohr advanced a model for hydrogen that accounted for hydrogen’s line spectrum and addressed the flaw in Rutherford’s model.  Bohr retained the “solar system” image  Dense nucleus and e - circling the nucleus  Bohr added…  e- orbits could only have certain sizes and energies, other orbits were forbidden  Bohr quantized the model of the atom

12. Bohr’s model

13. A closer look at Bohr’s model…  The lowest energy value the e - can have is n = 1  This is most stable energy state; called the “ground state”  When an e - absorbs quantum energy it leaps to a higher energy level (“excited state”). The e - returns to ground state, emitting energy.

14. A closer look at Bohr’s model…  The emitted energy comes out as a photon that corresponds to the energy difference allotted for a given orbit.  n = 5 → n = 2 (violet)  n = 4 → n = 2 (blue-green)  n = 3 → n = 2 (red)  n = 6 → n = 2 (barely visible)

15. And…another one bites the dust!  The electron does return to n = 1, but that transition is so energetic that the photon is in the ultraviolet region.  Bohr’s model only works for hydrogen.

16. The wave mechanical model  1924 - Louis deBroglie shows that the e - has wave properties.  1926 -Erwin Schrödinger applied the mathematics of waves to electrons.  e - circles all around nucleus  Found that a whole # of e - fit the orbits described by Bohr for hydrogen

17. What about the space between the orbits?  Between the "orbits", the wave would not fit right; when it circled around to its starting point it would not meet up correctly.  Such a wave would self-destruct  Schrödinger worked out the math that described the three- dimensional waveforms of the electron at various energies.  The waveforms are called orbitals to distinguish them from orbits (orbits can be calculated and predicted)

18. A closer look at an orbital  Orbitals are waveforms.  Can’t pinpoint location of e -  Probability region ( 3D space in which most likely to find e - )  Most useful to look at e - in terms of energy  Relates to wave and particle nature (dual nature)  So long to “solar system” model  Particle personality = the electron is just somewhere within the cloud (position and velocity unknown)  Wave personality =the electron is the cloud, a standing wave of electron energy electrons.

19. Waveforms are identified by three characteristics electrons.  Principle energy level (n) = describes the size of the electron wave (how far it extends from the nucleus).  n increases 1 to ∞ (orbital energy increases).  Each energy level contains n sublevels.  Level 1 = one sublevel (s)  Level 2 = two sublevels (s, p)  Level 3 = three sublevels (s, p, d)  Level 4 = four sublevels (s, p, d, f)  Each sublevel contains 1 or more orbitals  s = 1 orbital  p = 3 orbitals *Each orbital holds 2 e -  d = 5 orbitals

20. s orbital and p orbital

21. Aufbau Principle and e - configuration  Aufbau (“to build up”) Principle - the electron is most stable in the ground or lowest energy state.  To describe energies of all e - in atom, we need to specify waveforms we can use e - configuration.

22. Let’s practice e- configuration…  Write the e- configuration of: a) Be b) B c) C

23. The Periodic Table and e - configuration