unit 3:organization of matter quiz

democritus

coined the term "atom" for natures basic particle

aristotle

didnt believe in "atom" idea; thought matter was continuous of earth, air, fire, and water

alchemy

practical pursuit of transmutation/transformation of elements into one another, like changing elements to gold for wealth, which didnt work

in the late 1700s scientists believed..

elements that they've discovered thus far couldnt be broken down any more, which was false; knew that compounds for combos of elements; coined term "chemical reaction"=transformation of substances into 1+ new subs.

by the 1790s..

instruments improved and lead to discovery of basic laws

law of multiple proportions

if 2+ dif. compounds are made up of same 2 elements, the masses of 2nd element combined w/ a certain mass of the 1st can be written as ratios of small whole #s; ex. CO, CO2; never CO1.5, etc.

john dalton

continued from democritus' work; proposed atomic theory in 1801; tried to explain laws

dalton's true parts of theory

1. all matter made of atoms
2. atoms of dif elements can combine in simple, whole ratio #s to make compounds
3. in chem rxns, atoms are combined, separated, or rearranged

one false statement of dalton's theory

atoms of same elements are identical in size, mass, etc.; isotopes make this statement false

the other false statement of daltons theory

atoms cant be created nor destroyed; nuclear rxns make this false (mass defect from splitting atoms)

isotope

atoms of the same element w/ dif masses

atomic structure

identity and arrangement of smaller particles w/in atoms

2 main regions in atom

nucleus and electron cloud

nucleus

small region of protons and neutrons

electron cloud

contains electrons; comparatively large in volume to nucleus

discovery of electrons

by jj thomson and robert millikan; by looking at relationship btw electricity and matter by way of cathode ray tubes

in a cathode ray tube..

electricity flows from cathode (-) to anode(+)

jj thomson

1897, found cathode rays made up of electrons; found it had a large charge when compared to its tiny mass

electron mass

9.1 x 10^-28 g

robert millikan

1909, continued from thomson's experiments, found mass of electron by Oil Drop Experiment (used this, didnt develop this experiment)

it was confirmed that the electron..

has the smallest possible neg. charge and are in all elements

b/c atoms have neutral charge..

there must be a positive charge to balance electrons

b/c mass of e- is so small..

atoms must have additional particles that account for most of their mass

nucleus found by..

ernst rutherford in 1911 w/ help of ernest marsden and hans geiger

rutherford's gold-foil exp...

gold foil was bombarded by protons; the alpha (He nucleus) particles that were shot back were repelled by nucleus that also had pos. charge

nucleus

positively charged, dense center of atom that has almost all atom's mass but takes up an insignificant fraction of its volume

chadwick

discovered neutrons

size of atoms

measurements made myh looking at radius (mid. of nucleus to edge of electron cloud)

units of atoms

picometers, ranging from 40-270 pm

mass of p+

1.673 x 10^-24 g

mass of neutron

1.675 x 10^-24 g

# of p+ determines..

atoms identity

magnetic field in atom..

partly keeps electrons from coming to positive nucleus

nuclear forces

short range proton-proton, proton-neutron, and neutron-neutron forces that hold nuclear particles together

atomic #

# of p+; identifies element; on PT, placed in order of increasing at. #s; same # of electrons unless a charged is stated

isotopes (nuclide)

atoms of same element w/ dif masses (b/c of dif # of neutrons)

hydrogen isotopes

1. protium - 1p+, 1e-, 0n (99.985%)
2. deuterium - 1p+, 1e-, 1n (nuclear power plants)
3. tritium - 1p+, 1e-, 2n (very rare, radioactive, breaks down easily)

mass #

total # of p+ and n0 in nucleus of an isotope

2 ways to designate isotopes

1. hyphen notation (Hydrogen-3; U-235)
2. nuclear sumbol - symbol for element w/ mass # superscript and atomic # subscript, both to left of symbol

to find composition of nucleus

mass # - atomic # - # of neutrons

how many p+, e-, and neutrons in carbon-13

6 p+, 6 e-, 7 n0

write hyphen not. for element whose neutral atoms have 7 electrons and 9 neutrons

N-16

relative atomic mass

mass of an atom written in atomic mass units (amu)

1 amu

1/12 mass of carbon-12 atom; 1.6605402 x 10^-24 g

carbon-12

chosen as standard for atomic mass and all other atoms are compared to this b/c it has exactly 12 amu

mass of any isotope found by..

comparing it to mass of C-12

avg. atomic mass

the weighted avg. of atomic masses of the naturally occuring isotopes of an element; what you find on the PT

avg atomic mass equation

isotope #1 + isotope #2
(% x rel. mass) (& x rel. mass)