Unit 10. Electrons in Atoms. Light as Energy. Wave Theory of Light : James Clerk Maxwell (mid-1800s) Electromagnetic radiation – a form of energy that exhibits wavelike behavior as it travels through space
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Electrons in Atoms
Wave Theory of Light:
Light as a Wave
A. Wavelength ( “lambda”)
B. Frequency( “nu”)
B. Frequency( “nu”)
C. Wave Velocity (speed) = c
Example #1: The wavelength of the radiation which produces the yellow color of sodium vapor light is 5.89 x 10-7 m. What is the frequency of this radiation?
Example #2: What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz?
- Light is emitted in small discrete amounts called “photons”
Example #1: What is the energy of a photon from the violet portion of the rainbow if it has a frequency of 7.23 x 1014 s-1?
Example #2: What is the energy of a photon from the green portion of the rainbow if it has a wavelength of 4.90 x 10-7 m?
Light is both a wave and a particle!!!!
Valence electrons in calcium reside in the n = 4 energy level
A. What does the coefficient mean?
Principle energy level
B. What does the letter mean?
Type of orbital (sublevel)
C. What does the exponent mean?
# of electrons in that orbital
1. Determine the total number of electrons the atom has (for neutral atoms it is equal to the atomic number for the element).
atomic # = # of p+ = # of e- =
2. Fill orbitals in order of increasing energy.
3. Make sure the total number of electrons in the electron configuration equals the atomic number.
When writing electron configurations:
Write electron configurations for the following elements:
i. Where are the noble gases on the periodic table?
ii. Why are the noble gases special?
iii. How can we use noble gases to shorten regular electron configurations?
1. Look at the periodic table and find the noble gas in the row above where the element is.
2. Start the configuration with the symbol for that noble gas in brackets, followed by the rest of the electron configuration.
Practice! Write Noble Gas Configurations for the following elements:
Think of these in terms of a hotel:
Orbital diagrams use boxes (sometimes circles) to represent energy levels and orbitals. Arrows are used to represent the electrons.
Don’t forget - orbitals have a capacity of two electrons!! Two electrons in the same orbital must have opposite spin so draw the arrows pointing in opposite directions.
Example: oxygen 1s22s22p4
Practice! Draw orbital diagrams for the following elements:
If the orbital diagram for sulfur looks like this:
How many unpaired electrons are in the valence shell of a sulfur atom?
Does this make sense regarding the charge on a sulfur ion?