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Chemistry Lecture Notes

Atomic Structure


Jay Holt of Atlanta found himself recently in a coffee shop in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:

Holt: Your coffee can't be chemical-free. Coffee is composed of chemicals.

Waitress: Our coffee supplier uses water to remove the caffeine, but some companies use chemicals like ethyl acetate.

Holt: Water is as much a chemical as ethyl acetate.

Waitress: No, it's not. Anyway, our coffee is 99.99% caffeine free.

Holt: But then it still has 0.01% caffeine, and caffeine is a chemical too.

At this point, Holt says, he sensed that the waitress was becoming annoyed, plus the line behind him was growing, so he went off to regroup and drink his “excellent cup of chemical-free cappuccino.”


In the April issue of in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:Newskokie, the news organ of Skokie, IL, Larry Berman of that village saw an article suggesting the use of “nonchemical control methods” to fight grubs in your lawn. Among the nonchemical controls suggested was “a solution of castor oil, liquid detergent, and water.” Berman telephoned the Skokie government's Environmental Division to ask why castor oil and detergent were not chemical. The lady who answered told him because “chemical is poison—if it's not poison, it's nonchemical.”

 

Owing to her job of negotiating leases for store space in a shopping center, Leonie Batkin-Allen of Los Altos, CA, keeps up with the retailing business. Thus she noted the other day in Women's Wear Daily that Clinique Laboratories Inc. soon plans to introduce “the first chemical-free sunblock.” Instead of chemicals, the product will be based on titanium dioxide, which, Allen says, “I am very familiar with as my husband is in the paint industry.”


Chemistry: Everything! in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:


  • Explanations in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:

  • hypotheses

  • theories (models)

  • Observations

  • experiments

  • measurements

  • scientific laws

Scientific Process


  • Law of conservation of mass in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:

    • - in a chemical reaction, no mass is gained or lost

    • Antoine Lavoisier (late 1700s):

      • red oxide of mercury  mercury metal + oxygen gas

      • 10.0 g 9.26 g 0.74 g

  • Law of definite proportions

    • - all samples of a compound have the same proportion, by mass, of the elements present

      • carbon monoxide

      • carbon dioxide

always the same

proportions


Dalton’s postulates in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:

  • ~400 BC Democritus: “atomos” (indivisible)

  • -but Plato & Aristotle argued against it

  • -ignored for > 2000 years

  • 1803 John Dalton proposed:

  • (> 100 years before the discovery of the nucleus, protons, and electrons!)

    • 1. All matter is composed of tiny, indestructible (indivisible)

    • particles called atoms.

    • 2. All atoms of a given element are the same; atoms of different

    • elements are different.

    • 3. A compound is composed of atoms in a fixed number ratio.

    • 4. Chemical reactions involve only exchanges of atoms; atoms are

    • neither created, destroyed, nor transmuted.


  • Dalton’s theory explained: in a local mall. His college-age waitress wore a button touting the shop's decaffeinated coffee as “100% chemical-free.” Holt, wishing to be a good ambassador for chemistry, started the following dialogue:

    • the Law of Conservation of Mass:

      • 2HgO  2Hg + O2

    • the Law of Definite Proportions:

      • CO2

  • and predicted:

    • the Law of Multiple Proportions:

      • e.g., CO2 O/C = 2.67

      • CO O/C = 1.33

no loss or change in atoms,

 no loss or gain of mass

always same number (same proportion)

of same atoms (same masses)

(simple whole number ratio)


1838, Michael Faraday: cathode rays – mysterious, invisible carriers of electric current

1874, George Stoney: “electrons” – fundamental unit of electric charge

1897, J. J. Thomson: mass/charge ratio of electron – about 2000  smaller than smallest known particle (H ion)

1909, Robert Millikan: charge on electron – 1.6  10-19 coulomb

 mass of electron = 9.1  10-28 g

1911, Ernest Rutherford: nuclear model

1920s: protons

1932, James Chadwick: neutrons


< 0.05% of mass

Analogies: size: 1 million C atoms ~ thickness of a sheet of paper

73 million Cu atoms ~ diameter of a penny

emptiness: nucleus/electron cloud ~ pinhead/baseball stadium

mass: if matter were composed of only nuclear material,

a matchbox full would weigh 25 billion tons


235 invisible carriers of electric currentU

92

Isotopes: atoms with the same atomic number (same number of protons)

but different masses (different number of neutrons)

12C 13C 1H 2H 3H 79Br 81Br

deuterium tritium

Notation: AX

X = symbol for the element

Z = atomic number = number of protons

A = mass number = number of protons + neutrons

 number of neutrons = A  Z

e.g., How many neutrons are in 12C, 206Pb?

e.g., What is the mass number of phosphorus with 16 neutrons?

Z

identity


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