1 Chapter 11Modern Atomic Theory 2 Electromagnetic Radiation
Light is a form of electromagnetic (EM) radiation
All forms of EM radiation are types of kinetic energy
See page 306
3 EM Radiation
EM radiation can be described as traveling in waves or as packets of energy called photons
4 EM Radiation
Describe each form of EM radiation by its
Energy of its photon
All forms of EM radiation travel at the speed of light (c)
Wavelength x frequency speed of light
6 EM Radiation
The longer the wavelength the
lower the frequency and the lower the energy of the EM radiation
The shorter the wavelength the
higher the frequency and the higher the energy of the EM radiation
7 EM Radiation
Compare the wavelength frequency and energy of
Ultraviolet light and infrared light
8 EM Radiation
The higher the energy of the EM radiation the more damaging it is to living tissue.
CONSIDER GAMMA RAYS X-RAYS AND UV LIGHT
9 Emission of Energy by Atoms
Thanks to the work of Bohr we know that
When atoms are energized by an input of energy their electrons are excited (energized)
When excited electrons return to lower energy states they emits energy in the form of light.
Emits photons of energy
Energy of the photons emitted depends upon how excited the electron was.
10 Bohr Experiment (1911)
Bohr excited hydrogen atoms by running electricity through a tube of hydrogen gas.
The gas gave off a pink light.
11 Bohr Experiment (1911)
Bohr aimed a beam of the pink light at a prism
Found the pink light generated a line spectrum not a continuous spectrum
Line spectrum specific colors of light observed
Continuous spectrum all colors of light present
12 Bohr Experiment (1911)
He observed 4 bands of color (pg 310)
Purple (410 nm)
Blue (434 nm)
Green (486 nm)
Red (656 nm)
13 Bohr Experiment (1911)
He then calculated the energy of each color of light
_____________ was the highest energy and _____________ was the lowest energy.
14 Bohrs Interpretation of the Data
The electrons circle the nucleus in orbits of specific energies.
Larger orbits are of higher energy than smaller orbits
15 Bohrs Interpretation of the Data
Electrons are always in one of the circular orbits.
The electricity excites electrons and allows them to move to higher energy orbits.
16 Bohrs Interpretation of the Data
When the excited electrons return to lower energy orbits they emit energy in the form of light.
The difference in energy levels between the orbits determines the energy of the light given off.
17 Bohrs Interpretation of the Data
Because only certain wavelengths of light are emitted only certain energy changes are occurring
4 bands of light therefore 4 possible energy changes are possible
Say energy levels are quantized meaning only specific energy levels are available to electrons.
18 Bohrs Model
When Bohrs mathematical approach was applied to other elements it didnt work.
Bohrs model of the atom has been revised to replace the circular orbits with wave mechanical model of the atom
19 Modern Atomic Structure
Still picture electrons to be at specific energy levels but no longer picture them as traveling in circular orbits.
The current model of the atom locates electrons in orbitals.
20 Modern Atomic Structure
Orbitals are very different than Bohrs orbits
Read the firefly analogy on page 313
Each orbital is of a specific energy size and shape
Each orbital can hold a maximum of 2 electrons of opposite spin (Pauli exclusion principle)
The exact path of an electron in an orbital is not known.
Heisenberg uncertainty principle states that it is impossible to determine the location and path of an electron at the same time
Orbital shapes describe the region in space where an electron will be found 90 of the time.
24 Modern Atomic Theory
Atoms have specific energy levels in which electrons may be found.
Called Principal Energy Levels (PEL)
PEL farther from the nucleus are larger and of higher energy.
Assign a number (n) to each PEL
25 Modern Atomic Theory
Within each PEL are sublevels
Sublevels are named s p d and f
The larger the PEL the more sublevels it contains
26 Modern Atomic Theory 27 Modern Atomic Theory 28 Modern Atomic Theory
Sublevels contain orbitals.
29 Describing Orbitals
See pages 314/315 for diagrams of the orbitals
S orbitals are spherical
The 3 p orbitals are
30 (No Transcript) 31 (No Transcript) 32 Putting it All Together
Unless they are excited electrons always occupy the lowest energy orbital with room.
Electrons enter orbitals of a given sublevel one at a time before pairing up (Hunds rule)
Consider 2 electrons in a p sublevel
33 The fun part!
Our goal is to write the following for atoms and ions
Lewis dot symbol
Our goal is also to
Identify core and valence electrons
Electron configuration shows the number of electrons in each sublevel
Box/energy diagram shows the number of electrons in each orbital
Orbitals are shown as boxes
electrons are shown as arrows
Lewis Dot Symbol shows the valence electrons as dots around the symbol for the element
Maximum of 2 electrons per side of the symbol
Valence electrons all the electrons in the highest occupied PEL
Valence electrons are the ones involved in bonding
Core electrons all electrons not considered valence electrons
37 You will be given this.
Sublevels listed from lowest energy to higher energy
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p.
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