SHEM 1630- Rik Blumenthal Chapter 2 Lecture Notes
Homs and the Periodic Table
Atom: smallest quantity of matter
ou still retaining properties of
the matter art
Atoms are made of subatomic particles - electrons, protons neutron
The discovery of subatomic particles was product of research involving radiation'
Cemission & transmission of energy
Subatomic Particles & Atomic structure
•1800s - research involving radiation
w/ "new toys' on
•Cathode Ray Tube (5.5. Thomson): DISCOVERY OF ELECTIONS otwo metal plates negatively (-) and positively (+) charged
sealed in glass tube z a connected to voltage source. o(-) charged plate - cathode - emits cathode ray (stream
We also discuss several other topics like What is the central dogma?
of (-) charged particles
o Cathode raymoves towards (t) charged plate - anede. We also discuss several other topics like Where is timbuktu located?
If you want to learn more check out What is the period of relaxation in the heart?
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causes cathode Trays to glow
o placing the different poles of a magnet mear Don't forget about the age old question of What temperature has a numerical value that is the same in degree celsius as it is in degree fahrenheit?
visible cathode rays can show what the cathode
rays' charge is * If the ray deflects the positive end of magnet,
it must be positively charged. If it attracts the u se end of magnet, it must be negatively charged (Based on Coulomb's Law: LIKE repels LIKE
- OPPOSITE attracts OPPOSIT The cathode rays deflected (-) end and attracted (t) e If you want to learn more check out Sleep restores what?
- We also discuss several other topics like What is cosmological principle?
&cathode rays must be made of (-) charged partic
I later named electrons. o In a similar experiment, Thanson used two electric
plates (+) n (-) charged and the ray again deflected by the (-) plate and attracted by the (+) plate
V* SAME CONCLUSION
•After discovering electrons, Thomson Imeasured degree of deflection of cathode rays
Determined charge-to-mass ratio of electrons]
-1.76 *10* Cly (coulomb's gram)
1909 Robert Millikan perform's le Oil drop experiment to
determine charge and mass of electron.
• Oil droplets placed in enclosed box w/ electric field
Drops picked up static charge from surrounding air
• Drops were suspended (floating") in the electric
The magnitude of electric field necessary to keep drop Suspended depended on amount of charge the drop got from the air. from this, Millikan discovered charge of hatron
1 = -1.60 22x10-19 C
He then used charge to-mass ratio to convert charge to mass: Mass of electron = 9.10*10-28
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•Radioactivity: spontaneous emission of radiation
More experimentation w/ cathode rays revealed 3 types of radiation
Henri Becquerel discovered some rocks emit radiation Ispontaneously (on their own) & concluded 3 types of radiation to be
Alpha Rays (2) -positively charged © Beta Rays (3) - regatively charged 3 Gamma Rays (8) - neutral charge
- Proposed Models of Atom
After Thomson's cathode ray experiment he proposed "Plum - Pudding Model of atomic structure:
harges to cancel out
positively charged area * It was already known atoms had
(-) charged particles, but atams are neutral, so they must have positive
elant (-) charges Thomson proposed electrons
charged matter. Thomson's model later dispproved by Ernest Rutherford's . Gold Foil Experiment Emitted Alpha particles (f) to thin sheet of gold foil
If Thomson's model is correct (meaning if atants had uniformly distributed (t) particles) o.
THEN j particles should be mostly deflected
Thomson Prin mass of positively embedded in m
and very few were completely deflected *Rutherford concluded
Atams must be made of mostly "empty space,"
or electron-filled space Lectroms
AND filempty spa There must be smallenbedd area
of positive particles- later named protons concentrated in center of atan bestelle
To Proton mass = 1.672 62 x 104 g 7 taldo Proton charge = 1.6022*10c
(same and opposite of election
- charge). Neutrons * Electrons & protons did not account for total mass of an
There must be other particles that are neutral contributing to a mass Neutron Mass: 1.67498+104]
Uledesca Atomic Number, Mass Number
Atomic number of an element is the # of protons and electrons of an element (since protons & electrons cancel out,
Protons define an elehere must be an equal #of both Ex. All Nitrogen atoms have ? protons
land ? electrons) Atomic mass is # of Neutrons + # of protons)
* Here is how atanic
a periodic table:
# and mass are notated
Notating atomic # and mass:
A un element
* Although atoms of same element have same atomic #
. (# of protons) atoms of same element can have different atomic
• Isotgeesiatoms w/ same atomic # but different
w #of neutrons therefore different atomic ma Ex Hydrogen has 3 isotopes
• How isotopes were discovered:
Two nuclei of same element were deflected by electric field BUT by different amounts
*The different degrees of deflection show there
med must be a different amount of con (+)
particles (neutrons) causing one isotope to be more attracted to the negative pole.
- Average Atomic Mass
measured in Average Mass Units Camu) ilamu = l. Cl 05 388*10*9947 he Calculating en Average Atomic Mass in amus
*Since elements naturally occur in different isotopes,
the masses of each isotope are averaged together to find Average Atanic Mass.
Average Atomic Mass = f,M, + f2M27 of a fraction representing natural abundance of
. isotope this is usually a percentage givenablem) M = mass # of isotope
Practice Problem Find the average atanic mass of 50% Li
507. 'Li *The fraction of "Li abundance is 50 or 150
The mass is 6. * The fraction of "Li abundance is 5000 or 50
The mass is ?
ang atomic praf, M, +f, MA = (50) (1) + (50) () = 6.5 amu
A Mole is a unit, (mol) It tells how many atoms are in a
sample of something
mitaceodathing mol = 6,022 x 1023 atoms Avagadro's Number
*Similar to how a dozen = 12 of somethi
Molar Mass on tells you the mass in grams of Imal of substance
units for molar mass are glmal
lamu is defined as Iglmal (lamu= Ig/mol) Ex. If the average atomic mass of legend is 1.00794 amn, then 1.00794 amu=1.00294 g/mol
AND If the average atomic mass of chlorine (CI) is 35.453 amu, then 35.453 amu = 35.453 g/mol
. If there are 50.0 g Felg) in how much Clzig) is there?
1 First, turn 50.0g
into mol Fe.
50. Og Fe Imel
E = .8953 ml Fe 55.843. Fe
Fe is taken from
3 Turn .8953 mol Fe
into mal cl
8953mol Fe 3 - Imol Cl. 2.686 mol cl
T. Tmel Fe Turn 2686 ml Cl Taken from able into gCl
2.686 mol Cl 35.453C1-Ja5.