chem exam #1 - sept 20 Flashcards
*also study week one notes
subatomic particles
the neutrons, protons and electrons in an atom
jj thompson and the cathde ray tube (1897)
- cathode ray tube (glass tube with most of air removed) is connected to power supply, this generates cathode rays (streams of e-)
- cathode ray passed into region beyond power supply
thompson found that by applying electric or magnetic fields…
he could bend the cathode rays
- this allowed him to calculate mass-to-charge ratio of e- (plum pudding model
robert millikans oil drop experiment
- generated very tiny oil drops that fell toward a neg-charged plate
- x-ray beam generates e- that stick to the oil drops
R.M. -1) by changing the charge on the plate he could…
- 2) by using mass-charge ratio from thompson…
1) - change the rate at which the oil drops fell
- determined charge of an e- (-1.602 x10^-19 coulomb)
2) calculated mass of an e- (9.109 x10 ^-31)
1896, Henri Becquerel discovered…
radiation being emitted by the mineral pitchblende
becquerel, curie’s, and rutherford discovered it was…
several types of radiation
rutherford found beta particles
(B) - equivalent in mass and charge to high energy electron
alpha particles
(fish) - equivalent in charge to 4He nucleus (2 protons, 2 neutrons)
alpha and beta particles get deflected in…
opposite directions by electric fields
rutherford gold foil experiment 1909
- had two graduate students test the plum pudding model
- bombard thin gold sheet w alpha particles
if the plum pudding model was correct…
the alpha particles should pass right through with some minor deflection
results of gold foil
- about 1 in 8000 particles deflected an average of 90 degrees, some bounced straight back (some fraction of alpha particles encountered a region of high pos. charge and mass)
1920, consensus that all nuclei contain …
protons
1932, neutrons were characterized in the…
nucleus
each proton and neutron has a mass of…
1 unified atomic mass unit, also called daltons (Da)
isotopes
atoms of the same element that have the same # of protons, but a diff # of neutrons on nuclei
nuclide
any atom of any element that has a particular # of neutrons in its nucleus
a
z X
a is mass number (#protons + #neutrons), z is atomic number (#protons)
*normally leave out atomic number
protons=
atomic #
neutrons =
mass = p + n
mass - p = n
electrons=
charge changes # of protons
7 horizontal rows called – and 18 columns called —
- periods
- groups/families
elements can be broadly categorized in two ways
1) as main group or transition metals
2) categorizes elements as metals, nonmetals or metalloids
all elements can form ions:
cations = pos. charged ions
anions = neg. charged ions
name the groups: 1, 2, 16, 17, 18
1- alkali metals
2- alkaline earth metals
16- chalcogens
17- halogens
18- noble gases
average atomic mass
weighted average of all isotopes of an element
natural abundance
proportion of a particular isotope, relative to all the isotopes of an element
calculating average atomic mass
multiple mass by abundance (/100) for each, then add all up (remember sig figs by underlining insig. digits)
molecular mass
the mass of one molecule of a molecular compound **mass of whole compound
(atoms/mol x atomic mass (u/atoms) = u/mol)
formula unit
the smallest electrically neutral unit of an ionic compound
formula mass
mass of one formula unit of an ionic compound *mass stays same even if ion all /form unit instead of molecule (label ion as element)
mole
an amount of a substance that contains a number of particles (atoms, ions, molecules) equal to avogadros constant
avogadros constant
the # of atoms/ions/particles in one mole of substance (6.022 x 10^23 particles/mole) * used to cancel out atoms to find moles
molar mass
g/mole, seen on the periodic table, is equal to atomic mass but expressed in g/mole
kilo
10^3
centi
10^-2
nano
10^-9
milli
10^-3
micro
10^-6
pico
10^-12
to get rid of log
put as power of 10
to get rid of ln
put as power of e
if just log(constant) or e^(constant)
simplify
sig figs
carry through + keep all, underline insignificant digits
if the plum pudding model was correct, what would results of gold foil be?
all alpha particles would have gone through
instead of gold foil, silver and aluminum, why might these foils of deflected fewer alpha particles?
smaller nuclei, odds of deflecting are lower
proton to neutron ratio when Z increases
ratio also increases
when calculation formula masses, why is the average masses of neutral atoms used not ions?
the mass of electrons is negligible
finding masses of formula units
just find atomic mass of the whole thing
do equal masses of two isotopes of an element contain the same number of atoms?
No.
g x mol/ –g (isotope #) x atoms/mol (avogadros constant)
- heavier isotopes have fewer atoms
find the number of moles given atoms or molecules
divide by avogadros constant
find moles given g
use molar mass
