Nature of Light chapter s – 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 2n 2 (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 1 2 = 2 electrons in the first shell *L level holds 8 electrons, n = 2 –next level up 2x 2 2 = 8 electrons *M level holds18 electrons, n = 3 –next level up 2 x 3 2 = 18 but 18 won’t fit in the 3 rd shell 8 is the maximum per level

However if The first shell holds 2 The second holds 8 And the third holds 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 level e- 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 photon Radiationless e- transition unstable state Wants 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 atoms H 1 proton, 1 neutron in the nucleus 1e- He 2 protons, 2 neutrons in the nucleus 2 e- 1p 1n 2p 2n Li, 3 protons, 4 neutrons 2 e- 1 e- 3p 4n Be 4p 4n 2e- Mass number (Protons + neutrons) Atomic number (# of protons in Nucleus)

B C N O 5p 5n 6p 6n 7p 7n 8p 8n 2e- 3e- 2e- 4 e- 2e- 5e-6e-

F Ne NaMg 9p 10n 10p 10n 11p 12n 12p 12n

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