When heated to high temps, gases give off light. If this light is passed through a slit, then through a prism or diffraction grating, the following patterns are seen: the lines are images of the slits bright-line spectrum Or if a light with a continuous spectrum is passed through a cold gas and then through a prism, you get: dark-line spectrum Why are there only separate (discrete) colors or lines?

Models of the atom: I. _____________________: In 1897, discovered e-’s were ________ mass and ____________________ charged. Since he also knew that atoms as a whole were ______________, he developed the ______________________________ model: J.J. Thomson low negatively neutral “raisin/plum pudding” One _________ : atom negative e- are the ____________ raisins positive charge is ________________ distributed in a___________________ uniformly “pudding”

_____________________ : In 1909, he fired ___________ particles (positively charged ____________ nuclei) at thin gold foil: Rutherford alpha helium Au foil a particle most ________ were not scattered or were scattered through _____________ angles only 1 in 8000 were scattered ____________ backwards only small His conclusion: The ___________________________ mass is concentrated in _________________________ at the atom's _____________ . He called this the ________________ of the atom. positively charged a very small volume center nucleus

As a result of Rutherford's experiment, the ___________________ model was developed: solar system One atom: ______________charge concentrated in the _____________ positive nucleus e- e- The e-'s ___________ the nucleus similar to how ________________ orbit __________________ . orbit the Sun planets 1/10,000 size of nucleus ~ ___________________ of the diameter of atom

_____________________with the solar system model: 1. Circular orbital motion  q _________________ 2. Accelerating q  ______________emitted from atom 3. Energy radiated  orbits will _____________________ 4. All atoms should ___________________in a short time 5. As they collapse, the e- should______________________ and the atom should _____________________emit a higher and higher ______________________ of light This should produce a ____________________spectrum. but _______________ spectra were observed. Problems accelerates radiation get smaller collapse revolve faster continuously frequency continuous discrete

Should see: But only saw: Why?

hydrogen, H III. The Bohr model for ___________________: 1. The 1 e- in H____________________ or __________ ____________the nucleus. It __________ in a ___________. The e- can only be found at ______________ (certain specially allowed) distances, which are unfortunately still called __________________ .  Each orbital has a _____________ number,____ . a/ The orbital _____________to the nucleus is called the ____________________and has n = ____. It has the ______________ energy = ______________. b/ The orbital furthest from the nucleus has the ______________energy and has n =_____. The energy of that orbital = ____. In that case, the e- is said to be _______________ , which means it is ________________ from the atom completely. does not orbit move around exists "state" discrete “orbitals.” quantum n closest ground state 1 lowest -13.6 eV highest ∞ ionized. removed

A. Bohr model of H atom: orbitals ----- = _____________ n=1 state of electron ground proton n=1 n= 2 to ∞ are called ____________ states one The ______ e- can be found at ______ level “excited” n=2 any n=3 etc… n= ∞ ionized  e- is___________

B. Photon _________________ : emission If an e- moves from to a ___________ energy orbital to a __________one, a photon of light is ___________ (given off). higher lower emitted photon _________ n=1 emitted n=2 n=3 The ____________ of the emitted photon: Eph = energy Ei - Ef

Reference Tables: page 3, top left. Ei = E3= -1.51 eV Ef = E2 = -3.40 eV Eph = Ei – Ef Eph = E3 – E2 Eph = – 1.51 – (-3.40) = 3.40 – 1.51 = 1.89 eV Easy way: IGNORE NEG. SIGNS AND JUST SUBTRACT!!!

C. Photon _________________ : absorption If an e- moves from a ___________ energy orbital to a __________one, a photon of light is ___________ (taken in). lower higher absorbed photon _________ absorbed n=1 n=2 n=3 energy The __________ of the absorbed photon: Eph = Ei - Ef

Ef = E3 = -1.51 eV Eph = Ei – Ef Eph = E1 – E3 Eph = 13.60 – 1.51 (ignore neg. signs) = 12.09 eV Ei = E1= -13.60 eV

D. Energy ____________________: conservation Emission (the ____________of light): birth photon ___________ Atom __________ energy as e- moves __________ loses removes energy down atom Absorption (the ____________ of light): death photon __________ Atom _________energy as e- moves_________ gains brings energy atom up energy gained energy lost In both cases: _________________ = ___________________

E. NOTES: 1. The technical term for “jumps” is____________________. transitions “inbetween” 2. No _______________________ jumps are allowed!!!  Only jumps from one ______________energy level or orbit to another ____________ energy level are allowed. allowed allowed only certain That is why _______________________ energy photons can be emitted or absorbed by atoms.. Since Eph = hf, only certain __________________(colors) are produced. frequencies That is why photon energies are ___________________(only certain values are allowed). “quantized”

Eph = Ei – Ef = hf ΔE "jump" = amount of e-____________ Bigger e- jumps  more _________ (transitions)  more _________  _____________ frequency photons  in ___________________ and beyond ΔE Eph higher blue, violet, UV Little e- jumps  less _________ (transitions)  less _________  _____________ frequency photons  in ____________________ and lower ΔE Eph lower red, IR emission absorption This is true for _______________ and _______________ .

high f low f little jumps BIG jumps

big little _______ transitions _______ transitions involve involve high low _______ energy light _______ energy light to the n=2 level Which transitions involve visible light?

And these? Where would these photons appear in the spectrum?

F. ________________ : Jumps from any level to n = ___ will ___________the e- from the atom. Ionization ∞ remove Ionization _________________: The _____________required to ___________an e- from an atom. potential energy remove What is the ionization potential for a H atom that has an electron in the ground state? 13.6 - 0 = 13.6 eV What is the ionization potential for a H atom that has an electron in the n=3 state? 1.51 - 0 = 1.51 eV

Notice: Mercury gas also has a fun diagram! But mercury has letters instead of numbers.

G. So where do _________________ (bright line) and _____________________spectra come from? emission absorption Unless the source is a low-density gas, interactions with other atoms blur the lines into a _________________ spectrum. continuous The missing colors are the __________ ones that were_____________ by the gas. same absorbed The heated gas absorbs, then emits only those photons from _____________ energy transitions. allowed

The same transitions produce same lines: photon absorbed photon emitted same transition

Ex: Atomic absorption spectroscopy: Each element has a _____________electron structure. The electrons make _______________transitions. Each transition produces a spectral ___________. The set of lines is a __________________for that element. unique unique line fingerprint slit ___________ spectrum absorption gas or liquid containing ______________ elements that absorb certain photons white light unknown prism _________: disperses light

Atmosphere of Sun – absorbs only photons that can “jump” levels of gases in it. That is how helium was discovered. Sun light after passing through atmosphere produces a dark line spectrum The Sun produces a continuous spectrum b/c the interaction of many gases blurs the energy levels.

Stars  broad lines  dense gas  compact star  red shifted  star moving away  blue shifted  star approaching increasing temperature

V. Bohr’s model could NOT explain why e- could only have ______________orbitals and energies. This was later explained by_________________________: discrete Louis DeBroglie The e- acts like a __________ and __________________ interferes with ___________ as it wraps itself around the ________________: wave constructively itself nucleus nucleus electron ________ orbits This can only occur at certain ______________ distances from the nucleus. discrete

The electrons form “standing waves” around the nucleus.

Electrons can act like waves. The wavelength’s of e- depend on their speed, but they are generally very small. That allows us to take pictures of very small things. colorized house fly fruit fly

surface of poison ivy

VI. The ___________Model: The electron is described by a ________ function, y.” The square: y2 is the ___________________ of finding an electron at a certain position. The e- is most likely to be found where the "probability cloud" is ________________ The electron is no longer thought to be located at a ________________ location, but may be ______________ . The locations of highest probability correspond to the positions of the old________________________. Cloud wave probability densest definite spread out Bohr orbits Bohr _________ orbitals: probability _________ clouds

Mass has a dual nature: particles or waves. mass sometimes acts like a wave mass usually acts like a particle light usually acts like a wave light sometimes acts like a particle Light has a dual nature: particles or waves.