Nature of Lightchapter 14

1600s – 1900s Is Light a wave or a stream of

particles

True nature of light

• It acts like a wave and a particle• Bohr –principal of complementary –sometimes

acts like a wave and sometimes like a particle, but never both ways at the same time.

• Wave length• Amplitude• Frequency• Speed (velocity) wavelength x frequency

1913 Bohr’s model of an atom’s structure 2n2 (basics of an atom before an electron jumps up to a higher

energy level) (trying to explain that an atom is stable)

• Atom’s shell is represented by, n –an energy level *K level holds2 electrons, n = 1 –lowest level

2 x 12 = 2 electrons in the first shell *L level holds 8 electrons, n = 2 –next level up

2x 22 = 8 electrons *M level holds18 electrons, n = 3 –next level up

2 x 32 = 18 but 18 won’t fit in the 3rd shell8 is the maximum per level

However ifThe first shell holds 2The second holds 8And the third holds 8, 2 + 8 + 8 = 18, so when we have a third level, we can store 18 electrons between levels K, L, and M.

• shells

KKK

K 2 e-

L 8 e-

M 18 e- NOOOO!Only 8 per level fit. Except only 2 in First level

• Bohr’s model gave them a place to start-it explained there were energy levels for the electrons and they exist only in certain circular orbits-it stated that the electrons did not fall into the nucleus but were attracted to it because of their – charge and the + charge of the protons in the nucleus. -it stated the electrons had only certain values while in these levels and that they didn’t lose energy while in these orbits.-it formed a model to use when explaining e- could gain or lose energy and jump or fall to the next level and give off a photon of light, heat, or energy (electron transition)

• Elements with the same # of valance (most outside shell) electrons have similar chemical and physical properties and are in the same group in the periodic table.

• 8 valance electrons = octet = stable• Holds onto its energy while in the level and

won’t spiral into the nucleus. He couldn’t explain why

Explaining light

e-e- electron gains (absorbs) energy, light, electricity, or heat and jumps up

to a higher energy levele- e- electron loses (emits) energy, light (photon), electricity, or heat and falls to a

lower energy level. Electromagnetic radiation (electromagnetic spectrum)

• Absorption and emission spectra is explained by the absorption and emission of energy during electron transitions

• Black lines = absorption• Bright lines (colors) = emission• Fluorescence/phosphorescence

fluorescence

(black light)High energy photon e-

e-

e- ground state

Heat released not a photonRadiationless e- transition

unstable stateWants to fall back to

ground level as soon as possible, excited state

Releases lower level photon

because it came from a lowered

level

Blue region of spectra

phosphorescence

__e-_ ___ metastable state

(excited state with an abnormally large lifetime

__e-_ delayed release of photon, falls back (appears to glow, at night)Ultraviolet daylight

Fills up during the day and holds, trapped and

excited

Shells of atomsH 1 proton, 1 neutron in the nucleus

1e-

He 2 protons, 2 neutrons in the nucleus

2 e-1p1n

2p2n

Li, 3 protons, 4 neutrons

2 e-1 e-

3p4n

Be

4p4n 2e-

2e-Mass number(Protons + neutrons)

Atomic number(# of protons inNucleus)

BC

N O

5p5n

6p6n

7p7n

8p8n

2e-

3e-

2e-4 e-

2e- 2e-5e- 6e-

F

Ne

Na Mg

9p10n 10p

10n

11p12n

12p12n

Al -13 protons and 14 neutrons Si -14 protons and 14 neutrons P -15 protons and 16 neutrons S -16 protons and 16 neutrons Cl -17 protons and 18 neutrons Ar -18 protons and 22 neutrons