Types of nuclear processes

Atoms can eject protons or helium nuclei & get lighter. They can swallow a neutron & spit out the proton to get heavier.

Whenever the # of protons changes, the atom type has changed.

Figure 5.6 Uranium Decay Path

Where does a 900-pound gorilla sit? When does radioactive decay occur?

Decay events—e.g. electrons detected for beta decay—most probable at first

As radioactive molecules become depleted, detected events decrease.

Announcement BreakMonday, November 5

I am baaaack! Should be available thru Wednesday.

Chapter 8 notes posted

Chapter 8 Personal Responsibility Problems Posted

There are a LOT of problems here….’cuz it really matters.

Average on Ex4: 53% (hey, it’s double the guess score!)

High: 90%

That was a hard test if you aren’t doing PRP’s.

Moral of this story•Do not smoke•Insecticides can ignite•Requires spark•Gives off energy•You have to be careful with chemistry

Time to do REAL chemistry: Starting Chapter 8

Stuff All Chemists Must Know:

•Conservation of Numbers: in a chemical rxn, atoms aren't changed, lost or made. •Same true of electrons, protons &  neutrons. •Conservation of Mass: mass isn't gained or lost either (neglecting those tiny losses in nuclear reactions).   •Chemistry goes by integer numbers -- albeit rather large integers in most cases.

Zillions

C + O CO  

We think: one atom at a time.

Reality: zillions of C’s, zillions of O’s, zillion’s of CO’s

Practice with sub-Zillion Numbers

One dozen cookies = 12 cookies

Two dozen eyes = 24 eyes

Four dozen yellow frosting zones = = 48 squeezes of yellow frosting tube.

Other convenient numbers: Baker’s dozen = 13 Gross = dozen dozen = 144

The mole: chemist’s dozen

Avogadro's number

= 602202035873921029561369 

= 6.02202035873921029561369 x 1023

This is a lie!!!!

•Earlier we said "Let one atom of H have 1 atomic mass unit" •Now, we have a problem, because H has 3 isotopes: •So.....we cannot use "hydrogen" as it usually exists (mixed isotopes) for our mass standard. •We must purify it. •Easier to purify carbon, so carbon became the mass standard: Atomic mass unit:

1 a.m.u. = 1/12th the mass of isotope = 1.660 x 10-24 g.

A single atom of weighs 12 x 1.660 x 10-24 g.

Atomic Mass Unit:  where Avogadro's number comes from.

Avogadro’s Number: inverse of a.m.u.

How many atoms of are in 12.000 grams

of pure isotope   

Answer: (12 grams of )

= 6.022 x 1023 atoms

1 atom12 x 1.660 x 10-24

grams ( )

It’s the same as the number of atoms of hydrogen in one gramof hydrogen (assuming only the “normal” hydrogen isotope).

Avogadro’s Number: Fixing that Lie

We said: 602202035873921029561369

6.02202035873921029561369 x 1023

We really only know the first few numbers, so:

6.022 x 1023

Why did I fib?To emphasize that Avogadro’s number is an integer, just as a dozen or a gross are integer numbers. All the things we do with ordinary integer numbers we also do with Avogadro’s number. Compare the national debt, another “big” number:

Your share: $20,259.19

The Outstanding Public Debt as of 05 Nov 2001 at 07:26:45 PM GMT is:

Irrelevance of Detail

Wouldn’t $5.78 x 1012 be close enough?

Your share: $2.0 x 104 = $20,000

Compound Formula and Molecular Weights

Molecular weight: how many a.m.u. per molecule (same as how many grams per 6.022x1023 molecules) 

Formula weight: how many a.m.u. per formula (same as how many grams per 6.022x1023 repeats of  the formula)

Get Molecular weight:

Example in notes: CH4

Example here: benzene, C6H6

Get Formula weight for :

Ba(HCO3)2

How many carbon atoms in 7.8 grams of benzene, C6H6

How many hydrogen atoms?

Comparable automobile problem1965 Plymouth Barracuda’s weigh 3,000 pounds.

How many tires per 9,000 pounds of Fishcar?

Answer: 12 (not counting the spare)

How many cubic inches per 9,000 pounds of Fishcar?3 x 273 = 819 cubes

How many horsepower per 9,000 pounds of Fishcar?No one knows! About 750 (3 x 250)

Question:Which is potentially worth more?

1000 g of AgCl

or..... 1000 g of AgI

or..... 1000 g of Ag NO3 ?

or..... 500 g of Ag2CO3

Let's do another, perhaps a bit harder.   1. What is molecular mass of penicillin, C16H17N2O5SK

2. What is mass of 0.45 mol of penicillin?3. How many C atoms in 19.5 g of penicillin?4. What percentage of penicillin, by weight, is oxygen?

Actually, I don’t think thisis pencillin—maybe a derivative.

Dorothy Crowfoot Hodgkin, Nobel Prize 1964

ReactionsCH4 + O2 ---» CO2 + H2O

Unbalanced: a list of ingredients & results

CH4 + 2O2 ---» CO2 + 2H2O

Balanced: a correct recipe

Wheels + Pedals + Handlebar ---» BicycleUnbalanced: a list of ingredients & results

2 Wheels + 2 Pedals + 1 Handlebar ---» BicycleBalanced: a correct recipe

Blazing Bubbles

Chemical Equivalence: 

The symbol defines the relation between two compounds according to the particular balanced chemical reaction being considered! 

It acts like a conversion factor!

Consider: 2 KClO3 ----» 2 KCl + 3 O2

2 KClO3  2 KCl which is the same as: 1 KClO3   1 KCl

This simply means that one KCl will be produced for every KClO3 present in this reaction (other reactions that produce

KCl will be different).  

More about Chemical Equivalence:  2 KClO3 ----» 2 KCl + 3 O2

74.54 g of KCl 122.45 g of KClO3

We can also write:  2 KClO3    3 O2 

Or: 244.9 g KClO3 96 g O2

This means we get 96 g of oxygen for every 244.9  g of KClO3.

KClO3: 122.45 g/molKCl: 74.45 g/molO2: 32 g/mol

Chemical Equivalence in Use

How much oxygen can we get from 100 g of KClO3?

23

23 2.39

9.244

96100 gO

gKClO

gOgKClO

Another question on the same theme:

How much KClO3 will I need to produce 1 ton of O2?

Another Example (more complex, but also more fun....and a little depressing!)

How many tons of CO2 are produced by

burning 1000 gallons of gasoline? Assume density of gasoline is 0.692 g/ml and formula is C8H18.