light. the nature of light visible light is one type of electromagnetic radiation (em). other...
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Light
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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)
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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)
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How fast does a wave move? Depends on frequency (ν) and wavelength (λ) In a vacuum waves travel at 3.0 x 108 m/s
This is called the speed of light (c) c = ν x λ
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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.
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How to calculate the energy Well here’s the formula: E(energy) = h(planck’s constant) x ν (frequency)
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Rutherford’s Model How do we picture an atom? The nuclear model
Mimicks solar system: “sun” = nucleus “planets” = electrons
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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.
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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)
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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.
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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
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Bohr’s model
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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.
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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)
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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.
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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
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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)
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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.
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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
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s orbital and p orbital
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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.
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Let’s practice e- configuration…
Write the e- configuration of: a)Beb)Bc)C
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The Periodic Table and e- configuration
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The Periodic Table and e- configuration
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The Periodic Table and e- configuration