Transcript Chapter 4 - Rothschild Science

Chapter 4
Chapter 4
Everything you ever wanted to know about
where the electrons hang out!
Section 1: Early 1900’s
Scientists started doing a lot of experiments
looking at the absorption and emission of
light by matter.
Found that there is a relationship between
light and an atom’s electrons.
Light behaves as a wave
Transfer of energy
Draw the Wave!
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Amplitude: height of the wave from the origin to the crest
Wavelength ( ) : the distance between the crests (m, cm,
nm)
Frequency (v): number of waves to pass a given point per
unit of time (waves/second = Hz)
An Important Relationship
The frequency and wavelength of all waves,
including light, are inversely related.
As the wavelength of light increases, the
frequency decreases.
C = v
Where:
C= speed of light 3.00 x 108 m/sec
 = wavelength (m, cm, nm…)
v = frequency (1/sec or sec-1)
What is the frequency of a wave
that has a wavelength of 670nm?
C = v
Electromagnetic Radiation
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Includes radio waves, radar, microwaves, visible
light, infrared light, ultraviolet light, X-rays, and
gamma rays
Wave Particle Duality
http://www.youtube.com/watch?v=DfPeprQ7oGc
Sometimes Light Acts Like Particles!
What would happen if the frequency of the
wave increased so much that you could
hardly tell where one wave ended and
another began?
Light would start acting more like a particle
than a wave.
Photoelectric Effect
Looks at the emission of
electrons from a metal
when light shines on
the metal.
Light causes electrons to
be ejected from the
metal.
The Photon
Photon- a particle of
electromagnetic
radiation having no
mass, carrying a
quantum of energy.
Max Plank
Objects emit small packets of energy- Quanta
Quantum- the minimum quantity of energy that can
be lost or gained by an atom.
E = hv
E = Energy
h = 6.626 x 10-34 Js (Joule x sec)
V = frequency (1/sec)
What is the energy of a wave that
has a frequency of 4.5 x 1014 Hz?
E = hv
You should be ready to do the
WS….
Let the units be your guide!!!!!
So, what happens when photons
hit an atom and eject an electron?
The electron goes from
the ground state to an
excited state.
As the electron returns to
the ground state, it
gives off the energy
that it gained- LIGHT
Energy Levels
Energy levels are
not evenly spaced
• Energy levels
become more closely
spaced the greater
the distance from the
nucleus
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Work on you Electrons, Energy
and Light Pogil.
Warm Up
You have 20 minutes to finish up the POGIL.
Flame Test Lab
The flame you see is orange in color and you
determine th wavelength is about 590nm.
a. Calculate the frequency.
b. Calculate the energy.
You will looking at the excitement of electrons of
the metals in several ionic solutions
What did you really see?
The light you saw, was really a combination
of all the colors that were produced when the
electrons on the metal were excited.
Warm Up—Pass it up!
Many of you didn’t turn in the Unit 2 Work—
Vegium
Mole Activity (with work)
Mole Problems (the hard sheet)
Unit 3 Review
Check IC and turn it in by Monday!!
Spectral Analysis of Emitted Light
from Excited Atoms
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When the emitted light from excited atoms is passed through a prism, a
spectrum of discrete lines of different colors (separate energies) is
observed rather than a continuous spectrum of ROY G BIV.
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Different elements show different line spectra.
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Line spectra are used to identify the presence of different elements
Test Question Spectra
Each element has a
unique line-emission spectra
Emission Spectra
Atomic Line Spectrum
Interpretation of Atomic Spectra
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The line spectrum is related to energy transitions in
the atom.
Absorption = atom gaining energy
Emission = atom releasing energy
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All samples of an element give the exact same pattern
of lines.
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Every atom of that element must have certain,
identical energy states
Atomic Spectrum Activity
Using Atomic Spectral Data
Bohr Model
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Electrons orbit around a
nucleus
Each orbit has a fixed
energy and because of this
cannot lose energy and fall
into the nucleus
Energy Level of an
electron is the region
around the nucleus where
the electron is likely to be
moving
This helped explain the
spectral lines
Absorption- the electron
gains energy and
moves to a higher
energy level.
Emission- when the
electron falls to a
lower energy level.
The Quantum Model
Finally– the truth (as we know it!)
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Electrons can behave as both waves and particles.
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Electrons can be considered waves with specific
frequencies confined to the space around the
nucleus.
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Electrons can also be considered negatively
charged particles.
Schrodinger Wave Equation
Developed an equation that treated
electrons as waves and described the
location of electrons.
Helped lay the foundation for modern
quantum theory (atomic model).
Quantum Theory
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Estimates the probability of finding an
electron in a certain position
We denote the position of the electron as a
“fuzzy” cloud
This volume of space where an electron is
most likely to be found is called an orbital.
The atomic orbitals have distinct shapes