Lecture notes: CHEM103 Fall 2008 – September 23

1) BRIEF exam overview

2) Review: atoms/moles/mass conversions

BIG PICTURE: UNDERSTAND ELECTRONS BECAUSE THEY DETERMINE REACTIVITY

3) Energy concepts

a) transfer of energy between forms – CONSERVATION!

b) directionality of energy transfer between frames

c) energy & “stability” – opposites attract

4) LIGHT INTERACTS WITH MATTER (YES – ELECTRONS!)

a) Light as a wave

i) Electromagnetic (light) spectrum

ii) Conversions between wavelength & frequency

b) Light as a particle

i) Planck blackbody radiation

ii) Conversions between photon frequency and energy

5) Photoelectron effect: Einstein’s interpretation

SUMMARY:

* can also be: ions, electrons, molecules, albatrosses, etc…

SAMPLE PROBLEMS:

I. In 75 minutes of lecture, your body consumes 11.9 moles of oxygen gas.

1) WHAT MASS (IN g) OF OXYGEN IS THIS? 2) HOW MANY ATOMS OF OXYGEN DID YOU USE?

II. Oxygen is carried in blood by hemoglobin, bound to iron atoms within the molecule.

If a typical person has 5 liters of blood, and in that blood, a typical person has about 46mg/dL of iron.

1) HOW MUCH IRON (in moles) DOES PERSON’S BLOOD CONTAIN? 2) HOW MANY ATOMS DOES THIS REPRESENT?

CHAPTER 7 – LIGHT AND MATTER: THE ELECTRONIC STRUCTURE OF THE ATOM

WHERE ARE WE NOW?

BUT WHAT ABOUT THE ELECTRONS?

HOW ARE THEY DISTRIBUTED AROUND THE ATOM???

_{NOT REALLY} – THEY ARE DESCRIBED IN TERMS OF ENERGY, NOT OF POSITION!

so first we talk about energy…

ENERGY

RULE: conservation of energy (with one exception: E = mc²)

(1^st law of thermodynamics – “You can’t get something for nothing!” OR “You can’t ever win…”)

OR…In any process, the total energy of the universe remains the same.

Transfer of energy between different forms and different systems: examples… wind-up light, candle

Endothermic vs. Exothermic (endoergic vs. exoergic)

Key ideas: directionality of energy flow: SYSTEM vs. SURROUNDINGS!

SIGN of energy (positive vs. negative) and WHAT this means!

Examples: boiling water, making ice – what is the sign in each case?

Energy diagrams (refers to SYSTEM ONLY):

Example: energy diagram of a match

Energy flow and stability

Increase in stability = moving toward lower energy state.

So, why do negatively charged particles (i.e. electrons) move toward positive electrical fields???

(what does energy have to do with this process? – be able to DRAW it!)

GOAL: UNDERSTAND THE NATURE OF ELECTRONS

HOW? BY THE INTERACTIONS OF LIGHT WITH MATTER

Digression: how do particles and waves behave differently?

1) light can be described as a WAVE: using the concepts of wavelength & frequency

WAVE THEORY:

(“nu” – units of 1/seconds OR “Hz”)

c = l × n (speed = wavelength x frequency)

(lambda – units of length)

DON’T confuse wavelength and frequency with AMPLITUDE (or intensity)

SOUND EXAMPLE: What is the wavelength of a low-pitched sound wave?

frequency = 75 Hz (sec^-1)

given: speed = 340 m/s (speed of sound at sea level)

(application: placing speakers in a room; locating low pitches)

NOW WITH LIGHT: What is the frequency of the light from a red laser pointer?

wavelength = 660 nm

speed = 3.00 x 10⁸ m/sec (speed of light in a vacuum)