Download only that they did. democritus, an early greek philosopher, even had

Being asked what animal you'd like to be is a trick
question; you're already an animal.
Doug Coupland
CHEMISTRY IS ABOUT THE COMPOSITION OF
MATTER AND THE CHANGES IT UNDERGOES.
THE EARLY EGYPTIANS, CHINESE, AND
GREEKS WERE CONCERNED WITH HOW AND
WHY MATTER UNDERGOES CHANGE.
THEY PERFECTED MANY TECHNIQUES FOR
REFINING METALS, MAKING PAPER, DYEING
CLOTH, PRESERVING FOOD, AND THE
MUMMIFICATION PROCESS.
THEY DID NOT KNOW HOW OR WHY THESE
CHANGES OCCURRED - ONLY THAT THEY DID.
DEMOCRITUS, AN EARLY GREEK PHILOSOPHER,
EVEN HAD THE IDEA THAT IF YOU SUBDIVIDED
MATTER YOU WOULD REACH A POINT WHERE
YOU COULD NOT SUBDIVIDE IT ANY FURTHER.
THESE SMALL PARTICLES HE REFERRED TO AS
ATOMS.
HE WAS CLOSE TO THE TRUTH, BUT HIS
IDEAS WERE SUPPRESSED BY OTHER
PHILOSPOPHERS, ARISTOTLE AMONG THEM,
WHO THOUGHT MATTER WAS MADE UP OF
EARTH, AIR, FIRE, AND WATER.
AFTER THE DECLINE OF THE GREEK AND ROMAN
CIVILIZATIONS, THE ARABS CONTINUED MUCH
OF THE SCIENTIFIC TRADITION IN THE FORM
OF ALCHEMY.
ALCHEMY WAS A COMBINATION OF MEDICINE,
MYSTICISM, AND SCIENCE.
MANY ALCHEMISTS FOCUSED ON TRYING TO
TRANSMUTE OR CHANGE BASE METALS INTO
GOLD, MAKING THE ELIXIR OF LIFE, AND BASIC
MEDICINE.
ONE OF THE GREATEST WAS PARACELCUS, AN
EARLY SWISS ALCHEMIST.
THEIR WORK EVENTUALLY LED TO THE MODERN
SCIENCE OF CHEMISTRY.
JOHN DALTON (1766-1844), AN ENGLISH
CHEMIST, PROPOSED THE FIRST MEANINGFUL
ATOMIC THEORY.
1)ALL ELEMENTS ARE COMOSED OF TINY INDIVISIBLE
PARTICLES CALLED ATOMS.
2)ATOMS OF THE SAME ELEMENT ARE IDENTICAL. THE
ATOMS OF ANY ONE ELEMENT ARE DIFFERENT FROM
THOSE OF ANY OTHER ELEMENT.
3)ATOMS OF DIFFERENT ELEMENTS CAN PHYSICALLY MIX
TOGETHER OR CAN CHEMICALLY COMBINE IN SIMPLE
WHOLE NUMBER RATIOS TO FORM COMPOUNDS.
4)CHEMICAL REACTIONS OCCUR WHEN ATOMS ARE
SEPARATED, JOIONED, OR REARRANGED. ATOMS OF ONE
ELEMENT, HOWEVER, ARE NEVER CHANGED INTO ATOMS
OF ANOTHER ELEMENT AS A RESULT OF A CHEMICAL
REACTION.
IF YOU STARTED TO SUBDIVIDE GOLD, YOU
WOULD REACH A POINT WHERE YOU HAD
REACHED THE SMALLEST SUBDIVISION OR
PARTICLE - THE ATOM.
THESE PARTICLES ARE TOO SMALL TO BE SEEN
WITH THE NAKED EYE, AND UNTIL RECENTLY,
THEY WERE TOO SMALL TO BE SEEN EVEN
WITH THE BEST ELECTRON MICROSCOPES.
A GOLD ATOM IS 3 X 10-8 cm IN DIAMETER
AND HAS A MASS OF 3.3 X 10-22 g, OR
Dia = 0.00000003 cm
Mass = 0.00000000000000000000033 g
OTHER ATOMS RANGE IN SIZE FROM ABOUT
HALF THAT OF GOLD TO TWO TIMES AS LARGE.
ATOMS CAN BE SUBDIVIDED INTO SMALLER
PARTICLES IF WE HIT THEM WITH ENOUGH
ENERGY.
THE THREE SUBATOMIC PARTICLES WE ARE
GOING TO BE CONCERNED WITH ARE:
ELECTRONS
PROTONS
NEUTRONS
HOW MANY OF THESE EXIST IN A GIVEN ATOM
DETERMINES THE PROPERTIES OF THE ATOM.
ALL ATOMS CAN BE DIVIDED INTO TWO
PARTS:
1. THE NUCLEUS - THIS IS THE CENTRAL
CORE OF THE ATOM, AND IT CONTAINS
PROTONS AND NEUTRONS.
2. SURROUNDING SHELLS OF ELECTRONS.
WE OFTEN USE THE “SOLAR SYSTEM
MODEL” OF THE ATOM TO DESCRIBE
ITS PROPERTIES (BOHR MODEL).
A PROTON HAS A MASS OF 1.673 X 10-24 g
AND A CHARGE OF +1 (A UNIT POSITIVE
CHARGE).
A NEUTRON HAS A MASS SIMILAR TO THAT
OF A PROTON, 1.675 X 10-24 g, AND NO
CHARGE. IT IS NEUTRAL.
AN ELECTRON HAS A MASS OF 9.11 X 10-28 g,
WHICH IS A GOOD BIT SMALLER THAN THE
MASSES OF NEUTRONS AND PROTONS. IT
HAS A CHARGE OF -1 (A UNIT NEGATIVE
CHARGE).
USING THE MASSES OF THESE PARTICLES IN
GRAMS IS CUMBERSOME, SO WE USE THE
ATOMIC MASS UNIT (1 amu) FOR THE MASS
OF THE PROTON AND NEUTRON.
THE ELECTRON IS SO MUCH LIGHTER THAT WE
WILL ASSUME THAT ITS MASS IS 0 COMPARED
TO THAT OF THE PROTON AND NEUTRON.
PARTICLE
MASS
Amu
Location Charge
Neutron
1.67 x
10-24
1
Nucleus 0
Proton
1.67 x
10-24
1
Nucleus +1
Electron
0.0009 0
x 10-24
Shells
-1
outside
nucleus
ATOMS ARE NORMALLY NEUTRAL, SO THIS
MEANS THAT THEY HAVE TO HAVE THE SAME
NUMBER OF ELECTRONS IN SHELLS ABOUT THE
NUCLEUS AS THERE ARE PROTONS IN THE
NUCLEUS.
IN OTHER WORDS, THE NUMBER OF NEGATIVE
CHARGES HAVE TO BALANCE THE NUMBER OF
POSITIVE CHARGES.
# positive charges = # negative charges
OR
# PROTONS = # ELECTRONS
ATOMS OF DIFFERENT ELEMENTS DIFFER
FROM EACH OTHER BY THE NUMBER OF
PROTONS IN THE NUCLEUS AND THE
NUMBER OF ELECTRONS IN SHELLS
ABOUT THE NUCLEUS.
IT IS THIS NUMBER THAT DETERMINES
THE PROPERTIES OF THE ATOMS OF AN
ELEMENT.
THIS NUMBER IS THE
NUMBER.
ATOMIC
THE SIMPLEST ELEMENT IS HYDROGEN.
THE MOST COMMON FORM OF HYDROGEN HAS
A SINGLE PROTON IN THE NUCLEUS AND A
SINGLE ELECTRON IN A SHELL ABOUT THE
NUCLEUS.
HYDROGEN IS THE MOST ABUNDANT ELEMENT
IN THE UNIVERSE.
IF WE COULD LOOK AT THE DISTANCES INSIDE
AN ATOM, WE WOULD QUICKLY REALIZE THAT
AN ATOM IS MOSTLY EMPTY SPACE.
IF WE WERE TO EXPAND A HYDROGEN ATOM SO
THAT THE PROTON WAS THE SAME SIZE AS A
HUMAN, THE ELECTRON WOULD BE AT A
DISTANCE OF ABOUT 2 MILES AND WOULD BE
THE SIZE OF A SMALL BIRD.
WE MENTIONED EARLIER THAT IT IS THE
NUMBER OF ELECTRONS (OR PROTONS) THAT
DETERMINES THE PROPERTIES OF A NORMAL
ATOM.
THIS NUMBER IS CALLED THE ATOMIC
NUMBER.
WE’LL DEFINE IT AS THE NUMBER OF
PROTONS IN THE NUCLEUS, AND WE WILL
USE THE SYMBOL Z.
Z = ATOMIC NUMBER = # PROTONS
NOW, ELECTRONS HAVE VERY LITTLE MASS
COMPARED TO THE MASSES OF NEUTRONS AND
PROTONS.
SO, THE MASS OF AN ATOM, OR THE ATOMIC
MASS WILL BE THE SUM OF THE PROTONS AND
NEUTRONS IN THE NUCLEUS.
WE’LL USE THE SYMBOL A FOR ATOMIC MASS.
A = ATOMIC MASS = #PROTONS + #
NEUTRONS
IF YOU LOOK AT THE PERIODIC TABLE, THE
NUMBER GIVEN AT THE BOTTOM OF THE
ELEMENT BOX IS OFTEN NOT A WHOLE
NUMBER.
ALL ATOMS OF A GIVEN ELEMENT HAVE THE
SAME ATOMIC NUMBER (# PROTONS),
BUT, ATOMS OF A GIVEN ELEMENT CAN
HAVE DIFFERENT NUMBERS OF NEUTRONS.
THIS RESULTS IN ATOMS OF THE SAME
ELEMENT HAVING DIFFERENT ATOMIC
MASSES (# NEUTRONS + # PROTONS)
THESE ARE CALLED ISOTOPES.
THE ATOMIC MASSES GIVEN IN THE PERIODIC TABLE
REPRESENT AVERAGES BASED ON THE RELATIVE
ABUNDANCES OF THE NATURALLY OCCURING
ISOTOPES.
FOR EXAMPLE: THE ATOMIC MASS OF HYDROGEN IS
GIVEN AS 1.0079
THERE ARE THREE ISOTOPES OF HYDROGEN.
THE MOST COMMON ONLY HAS 1 PROTON IN THE
NUCLEUS, AND AN ATOMIC MASS OF 1
THE SECOND ISOTOPE, DEUTERIUM, HAS 1 PROTON
AND 1 NEUTRON IN THE NUCLEUS, AND AN ATOMIC
MASS OF 2.
THE THIRD ISOTOPE, TRITIUM, HAS 1 PROTON AND 2
NEUTRONS IN THE NUCLEUS, AND AN ATOMIC MASS
OF 3.
RATHER THAN WRITE THE NAMES OF THE
ELEMENTS, WE USE A SHORTHAND METHOD
FOR DESIGNATING THE ELEMENTS.
FOR EXAMPLE, THE SYMBOL FOR HYDROGEN IS
H.
THE SYMBOL FOR HELIUM IS He.
THE FIRST LETTER WILL BE CAPITALIZED,
AND IF THERE IS A SECOND LETTER, IT WILL
BE SMALL.
THE SYMBOLS ARE MOSTLY BASED ON THE
ENGLISH NAMES, BUT THERE ARE SOME
EXCEPTIONS.
IRON = Fe SODIUM = Na
LEAD = Pb
WE’LL LIVE WITH THE PERIODIC TABLE FOR THE
NEXT SEVERAL WEEKS.
THE PERIODIC TABLE IS ARRANGED IN ORDER OF
INCREASING ATOMIC NUMBER, Z.
FOR EXAMPLE, HELIUM, He, THE SECOND
ELEMENT, HAS AN ATOMIC NUMBER OF 2.
THIS MEANS THAT IT HAS 2 PROTONS IN THE
NUCLEUS AND TWO ELECTRONS IN SHELLS
ABOUT THE NUCLEUS.
THE ATOMIC MASS IS 4. THIS MEANS THAT IT
HAS TWO NEUTRONS IN THE NUCLEUS IN
ADDITION TO THE TWO PROTONS.
# NEUTRONS = A - Z = ATOMIC MASS - AT.
NUMBER
THE THIRD ELEMENT IS LITHIUM.
LITHIUM HAS AN ATOMIC NUMBER, Z, OF 3.
A = ATOMIC MASS = 7
SO, # NEUTRONS = A - Z = 7 - 3 = 4
HOW MANY ELECTRONS DOES LITHIUM HAVE?
THE THIRD ELEMENT IS LITHIUM.
LITHIUM HAS AN ATOMIC NUMBER, Z, OF 3.
A = ATOMIC MASS = 7
SO, # NEUTRONS = A - Z = 7 - 3 = 4
HOW MANY ELECTRONS DOES LITHIUM HAVE?
IF THE ATOMIC NUMBER, Z, IS 3, THIS MEANS
IT HAS 3 PROTONS IN THE NUCLEUS.
THE NUMBER OF ELECTRONS HAS TO EQUAL
THE NUMBER OF PROTONS, SO THE NUMBER OF
ELECTRONS IS 3.
THE FOURTH ELEMENT IS BERYLIUM, Be.
Z = 4 AND A = 9
HOW MANY NEUTRONS DOES Be HAVE IN
THE NUCLEUS?
HOW MANY ELECTRONS DOES Be HAVE IN
SHELLS ABOUT THE NUCLEUS?
MANY ELEMENTS HAVE ISOTOPES.
ISOTOPES ARE ATOMS WITH THE SAME ATOMIC
NUMBER BUT DIFFERENT ATOMIC MASS.
IN OTHER WORDS THEY HAVE THE SAME NUMBER OF
PROTONS IN THE NUCLEUS, BUT THEY HAVE
DIFFERENT NUMBERS OF NEUTRONS. HAVING THE
SAME NUMBER OF PROTONS MAKES THEM THE SAME
ELEMENT, AS THE NUMBER OF PROTONS (ATOMIC
NUMBER) DETERMINES THE CHEMICAL PROPERTIES.
THE ATOMIC MASSES GIVEN ON THE PERIODIC TABLE
ARE AVERAGES OF ALL THE NATURALLY OCCURING
ISOTOPES BASED ON RELATIVE ABUNDANCE.
IT’S INTERESTING TO THINK ABOUT THE
RELATIVE ABUNDANCE OF THE ELEMENTS.
IF WE CONSIDER THE UNIVERSE, HYDROGEN
IS BY FAR THE MOST ABUNDANT ELEMENT. IF
WE HAD 200 ATOMS, 182 OF THEM WOULD BE
HYDROGEN.
NEARLY 18 WOULD BE HELIUM.
LESS THAN ONE HALF OF ONE ATOM WOULD
BE THE REST OF THE ELEMENTS.
AT THE BIRTH OF THE UNIVERSE, MOST
EARLY MATTER WAS HYDROGEN AND HELIUM.
THE REST OF THE ELEMENTS WERE FORMED IN
THE CORES OF STARS.
IF WE LOOK AT THE ELEMENTAL MAKE-UP OF
THE HUMAN BODY, THE COMPOSITION WOULD
BE QUITE DIFFERENT AS COMPARED TO THE
UNIVERSE.
IF WE HAD 200 ATOMS, 126 WOULD BE
HYDROGEN AND 61 WOULD BE OXYGEN. AFTER
ALL, THE HUMAN BODY IS LARGELY WATER.
BUT, THERE WOULD BE 19 CARBON ATOMS
AND 3 ATOMS OF NITROGEN.
ALL OF THE OTHER ELEMENTS WOULD MAKE UP
THE REMAINING ATOM
http://www.ted.com/talks/just_how_small_is_an_
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