Download Atoms and atomic spectra

Atoms and atomic spectra
Atoms and Atomic spectra
• What are atoms made off? JELL–O?
• What happens when we hit atoms with various
stuff?
• How do atoms interact with light? Develop
model of how light interacts with and is
produced by individual atoms (Will help us learn
how atoms ‘work’)
Early ideas about atoms
Step 1: Shoot the JELL–O atom!
invisible!
• Atom - Greek “indivisible unit”
• The Blueberry-Muffin-Atom-Model (aka.
‘The Thomson model’): Uniform distribution
of positive charges with negative electrons
embedded in it.
But wait! We can get electrons from them
(scraping, chemical, or photoeffect) but no
positive charges. Hmmm?!...
Have a heavy blob that seems like grape JELL–O, and you
have gun with rubber bullets. How to find out what the middle
of the blob is like?
-
Have a heavy blob that seems like grape JELL-O, and you
have gun with rubber bullets. How to find out what the middle
of the blob is like? Shoot bunch of bullets into it and see this.
What is the inside like?
Q1:
Have a heavy blob that seems like grape JELL-O, and you
have gun with rubber bullets. How to find out what the middle
of the blob is like? Shoot bunch of bullets into it and see this.
What is the inside like?
a. hollow
b. solid JELL-O
c. hard heavy core surrounded by JELL-O
d. bunch of hard little objects distributed through blob
Have a heavy blob that seems like grape JELL-O, and you
have gun with rubber bullets. How to find out what the middle
of the blob is like? Shoot bunch of bullets into it and see this.
What is the inside like?
Hard heavy core surrounded by JELLO
Only one thing is reflecting bullets, sending them straight
back so must be hard and heavy.
Essentially Rutherford experiment and conclusion (TZD 3.12).
Rutherford shot alpha particles = 2 protons, 2 neutrons
n
pn Positive charge
Bullets =
p
The Rutherford atom:
Tiny nucleus with protons and neutrons (~99.98% of mass)
Surrounded by large diffuse cloud of low mass electrons
10-10 m
The Rutherford experiment
Detector
rutherford-scattering_en.jar
Let’s see how atoms behave
when shot-at! (with
(with electrons)
electrons)
n n
pnp p
p n
p
10-14 m
What happens if we bash atoms with
electrons?
In atomic discharge lamps, lots of electrons are given kinetic
energy (accelerated by a high voltage). When they bash into
atoms some of this kinetic energy is transferred to the atom
Atom get's excited!! (“Neon” lights, Mercury street lamps)
- 120V +
Cathode (hot metal, so
electrons can come out)
Anode (positive potential)
Note: ‘Anode’ and ‘Cathode’ have different meanings in physics or
chemistry. Remember ‘Cathode Ray Tube’ (CRT): Electrons
leave the cathode (in physics).
Use a grating to look at the spectrum of
the discharge lamps
Hold grating only by edges...oil from hands ruins grating!
Hold close to eye... See rainbow from lights. Turn grating
so rainbow is horizontal. (Rainbow appears quite a bit to
the side of the actual lamp.
Hydrogen
White light = whole spectrum.
Each type of atom produces
unique set of colors, called its
“spectrum”. None of the atoms
produces white light!
Na
Hydrogen
neon
neon
neon
Hydrogen
Each type of atom produces unique set of colors.
Discussion: What does this imply about electrons in atoms?
Implies that electrons only change between very specific energies.
Each time a photon is emitted an electron must be changing in
energy by that amount (releasing energy).
Only way for individual atoms to give off energy is as light.
Atoms are lazy - always want to go back to lowest energy state.
2. Excited atom ..electron
3. Electron
1. Fast electron
in atom goes to higher
jumps back to
hits atom
energy
Less KE low energy
Na Na
Na
NaNa
Hydrogen
Hydrogen
Hydrogen
Hg
Hg
Hg
Hg
Hg
What colors from white light?
What colors from neon?
What colors from hydrogen?
What from mercury?
What from sodium?
e
400
500
600
Wavelength (nanometers)
700
800
Higher
energy
e
Answer to clicker question
Q1: C
Ground
state
~10ns
Excited
state
e