109 CHEM General Chemistry University of Nebraska FALL 2008
Characteristics of Atoms
Atoms:
possess _______ contain positive _________ contain electrons occupy __________ have various properties attract one another combine to form molecules
How do we study atoms?
How do we study atoms?
The best tool for studying the structure of atoms is __________________________. What we call _____, is just one form of electromagnetic radiation. The properties of light help us understand _______________________.
Light moves even faster AND has shorter wavelengths than either ocean waves or sound waves. These combine to give light extremely ___________________________.
Waves of electromagnetic radiation that we see as light have really, really ________________ between 400 and 700 nanometers (a nanometer is one billionth of a meter!).
The Wave Nature of Light
Electromagnetic Radiation is a form of energy that has wave characteristics and that propagates through a vacuum at the characteristic speed of ________________ (the speed of light, c).
____________ ( = lambda) is the distance between successive peaks (or troughs) measured in meters or nanometers ____________ ( = nu) is the number of complete wavelengths, or cycles, that pass a given point in one second (s-1). Measured in hertz (cycles/second).
Frequency and Wavelength
c=
Amplitude and Intensity
A bright light is more _______ and has greater _________ than a dim light. The two waves shown here have the same wavelength, but different __________. The amplitude is represented by the height of the wave at its crest.
Let's Review....The Wave Nature of Light
Speed of light = wavelength x frequency
Units for speed of light = m x cycles = m cycle s s
An FM radio station transmits its signal at 88.1 MHz. What is the wavelength of the radio signals?
What is the frequency of light that has a wavelength of 1.40 cm?
The
Wave Nature of Light
There are many different types of electromagnetic radiation.
(wavelength and frequency = ______ (long relationship) wavelength : low frequency)
This is the spectrum produced by the light from a white light bulb. All the colors of the rainbow are present. Nothing is missing. This is a ______________ spectrum.
Interference
the interaction between waves is called ___________ when waves interact so that they add to make a larger wave it is called ___________ interference
waves are in-phase
when waves interact so they cancel each other it is called ____________- interference
waves are out-of-phase
Diffraction
when traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it this is called ____________
traveling _________- do not diffract
the diffraction of light through two slits separated by a distance comparable to the wavelength results in an interference pattern of the diffracted waves an interference pattern is a characteristic of all light _________
Diffraction
Quantized Energy and Photons
The wave model of light cannot explain some aspects of the behavior of light. The emission of light from electronically excited gas atoms, this is NOT a continuous spectrum!!
The Particle Nature of Light
The wave model of light cannot explain some aspects of the behavior of light... 1. The emission of light from hot objects... blackbody radiation Max Planck (1858-1947) Energy is _____________
n is a positive integer called a quantum number
1000 K
1500 K
2000 K
The Particle Nature of Light
Planck's Quantum Theory:
if an atom can emit (or absorb) only certain _________ of energy, the atom itself can have only certain ___________ of energy the atom is said to be quantized it exists only in certain fixed quantities of energy rather than being _____________ a "packet" of energy is a _______ (plural = quanta) and has an energy equal to h The smallest energy change for an atom in a given energy state: E = h (n = 1)
An atom changes its energy state by ____________________ one or more quanta of energy