Lecture notes: CHEM103 Fall 2008 – September 9

 

 

 

Outline for the day:

·        Guide to looking for patterns in Mini-Practical observations

·        Review:

a.     Mixtures: homogeneous vs. heterogeneous: definitions

·        Chemical calculations

a.     Dimensional analysis (discuss in lab)

b.     RULES for reporting numerical results

c.     Use of (non-programmable) calculators

d.     Uncertainty, error & sig figs! (handout)

·        Pre-history of the atom

 

 

CHEMICAL CALCULATIONS

 

I.                   DIMENSIONAL ANALYSIS or FACTOR-UNIT METHOD for problem solving – I’ll cover this in lab over the next week…

(also known as: WHY to ALWAYS use units)

 

II.                RULES FOR NUMERICAL RESULTS IN THIS CLASS: ALL reported numbers must include the following:

 

 

siL48593_01_10

                                                                                                           

 

KNOW the EIGHT assigned prefixes:

SI prefix

SI abbreviation

means

also known

tera–

T

× 1012

trillion

giga–

G

× 109

billion

mega–

M

× 106

million

kilo–

k

× 103

thousand

hecto–

h

× 102

hundred

deka–

D

× 101

ten

deci–

d

× 10-1

tenth

centi–

c

× 10-2

hundredth

milli–

m

× 10-3

thousandth

micro–

m

× 10-6

millionth

nano–

n

× 10-9

billionth

pico–

P

× 10-12

trillionth

femto–

F

× 10-15

quadrillionth

atto–

A

× 10-18

quintillionth

 

 

For example: the prefix, “tera–“ , abbreviated “T”, literally means “times 10 to the 12th power.”

 

 

 

a.     use of scientific notation and/or SI prefixes to clarify

          why AND WHEN these should be used for convenience and clarity

 

b.     correct-ish number of significant figures (within +/- one counts for credit)

                                      WHY do I care???  ERROR analysis

 

c.     SI units (actually, ALWAYS include units in calculations, not just on final answers!)

(derived from meters, grams, seconds, etc.)

              always use them unless told otherwise

 

d.     labels (use them just like units to describe WHAT you are calculating)

(this becomes REALLY important when we do stoichiometry)

 

 

 

I.                   USE OF CALCULATORS IN CHEMISTRY 103 – a common mistake…

 

 

untitled

 

 

 

 

 

 

 

 

à  the “times ten to the…” button.  USE it.

 

 

 

 

 

 

 

 

 

http://gratis-zoekertjes.onlinertjes.be/image/22422.jpg

 

 

 

 

 

 

 

à  the “times ten to the…” button.  Find it.  USE it.

 

 

 

 

 

 

 

 

 

 

We write: 6.022×1023 ;

 

We say: “6 point 022 times 10 to the 23rd power” ; 

 

We calculate: 6.022 “EE” 23  !!!  (or E or EXP, depending on brand)

 

 

II.                UNCERTAINTY, ERROR & SIG FIGS

 

SEE HANDOUT!!!

 

 

 

ATOMIC STRUCTURE: A BRIEF HISTORY

 

 

Group writing exercise:                   Define “ATOM.”

 

Getting away from our commonly held understanding to investigate how we came to this understanding…

WHY?         1) understand and support basis, not just memorize “fact”

                   2) analyze process of discovery (formation of models of understanding)

                   3) recognize limitations of models – prepare for more involved models

 

 

Further reading on the pre-history of the atom: http://dbhs.wvusd.k12.ca.us/webdocs/AtomicStructure/AtomicStructure.html

 

 

 

 

 

 

 

Greek scientific “philosophy” largely a mental and observational exercise – no experimentation:

 

…but generated TWO radically different WORLDVIEWS: atomistic VS. continuous

 

4th century B.C.

 

          Democritus (after Leucuppus)       

          Nature is: “atomos” separated by void

          1) infinite in number

          2) many varieties (shapes & sizes)

          3) in constant, random motion & collision

          4) collisions lead to deflection endlessly

          5) or to combination of particles to form substances which we can perceive

 

3rd century B.C.

 

            Epicurus

(read excerpts of Epicurus…

…and writings by Lucretius 95 – 55 B.C.)

 

 

vs…