Download Thursday, 1/29/09 - Liberty Union High School District

Bohr & New Atomic Model
Arrangements of Electrons in Atoms
Thursday, October 29th, 2015
1
The Development of a
New Atomic Model
•Rutherford’s model was incomplete
•How were electrons distributed?
•What prevents negative electrons from
crashing into positive nucleus?
•1900s-New Atomic Model (revolutionary)
•Relationship between light & electrons
2
How many Electrons Can Fit in
Each Energy Level?
Max # e =
2n2
Big Question:
Why?
• Energy level is also called
“principal quantum number”
• Energy Level = n
n
1
2
3
4
5
6
max. # electrons
2
8
18
32
50
72
3
There are two ways to state the location of
an electron…
• Quantum numbers – the location
of a specific electron
• Electron configurations – the addresses of every
electron in an atom (read the periodic table like a
book!)
Quantum numbers
• Principle quantum number (n) = identifies
the energy level of the electron
• Angular momentum quantum number (l) =
identifies the sublevel
• Spin quantum number = identifies the
orientation in the pair
5
6
Properties of Light
•Before 1900s-thought light behaved as a wave
•During 1900s-also has particle characteristics
•Electromagnetic Radiation
7
8
Electromagnetic Spectrum
High Freq
High E
Low Freq
Low E
9
Wavelength & Frequency
•Speed of light = 3.00 x 108 m/s
•Wavelength = distance between waves
•Frequency = # waves that pass point in
given time
c


c =
as  increases,  decreases
as  increases,  decreases
(slinky analogy)
10
11
Photoelectric Effect
•Emission of electrons
from a metal when light
shines on metal
•Light of minimum
frequency was required to
eject electron from metal
•Problem-wave theory of
light predicted light of
any frequency could eject
electron
12
Is Light a Particle?
•Max Planck-hot objects emit energy not as
waves, but in packets called “quanta”
•“quantum”-minimum energy that can be gained
or lost by an atom
•E = h
•E = energy
•h = Planck’s constant (6.626 x 10-34 Js)
• = frequency (in s-1)
13
Light as a Wave & Particle
•Einstein’s radical idea!
•Dual wave-particle nature
of light
•Called particles of light
“photons” (no mass)
•Explained photoelectric
effect (photon must have
minimum energy)
•Light is absorbed only in
whole numbers of photons
14
15
Emission Spectra
•White light
-continuous spectrum
•Hydrogen atoms
-line-emission spectrum
•Big Question
-Why did hydrogen
atoms only give off
specific frequency
(colors) of light?
16
The “Fingerprints” of Atoms
17
Atomic Spectra
• The atom is quantized, i.e. only certain
energies are allowed.
18
Neils Bohr Solved the Mystery
• Electron circled nucleus in
“orbit” of fixed energy
• Absorption-electrons can
“hop” from ground state to
excited state
• Emission-when electrons
“fall” from excited state to
ground state
• Energy difference
corresponds to hydrogen’s
spectral lines
• Ladder analogy
19
20
Remaining Mystery
• Bohr’s model
only explained
hydrogen atom
• What about
other elements
with more than
one electron?
21