Unit 3: The Atom

Democritus (discovery)

matter made of ‘atomas’; not divisible

John Dalton (discovery)

Dalton's theory

Dalton's theory

correct: all matter is composed of tiny particles called atoms, atoms combine in simple whole ratios to form compounds, atoms of 1 element cannot be changed into a new element during *chemical* reactions
incorrect: all atoms of an element are identical (bc isotopes), atoms cannot be created, divided, or destroyed (atomic bombs)

JJ Thomson (experiment)

cathode ray experiment

JJ Thomson (discovery)

discovered electron; plum pudding model

Millikan (experiment)

passed oil drops through a pin hole into the middle of the charged plate and noticed drops suspending between the plates

Millikan (discovery)

determined velocity + mass of an electron; 9.11 x 10⁻³¹ kg; electron charge = negative

Ernest Rutherford (experiment)

gold foil experiment

Ernest Rutherford (discovery)

discovered proton; atom mostly empty space; electrons (in empty-ish space) surround proton + neutron (in dense) nucleus; transmutation (i think?)

James Chadwick (discovery)

discovered neutron; w/ mass nearly equal to proton; w/ no charge (neutral)

Niels Bohr (discovery)

discovered electron orbits; 7 circular orbits around nucleus (energy levels)

electron (discoverer/location/charge/symbol)

discoverer: thomson; location: outside nucleus; charge: negative (-); symbol: e⁻; most of atom volume; discovered first

proton (discoverer/location/charge/symbol)

discoverer: rutherford; location: inside nucleus; charge: positive (+); symbol: p⁺; discovered second

neutron (discoverer/location/charge/symbol)

discoverer: chadwick; location: inside nucleus; charge: neutral (0); symbol: n⁰; discovered third

nucleus

dense; protons + neutrons; very dense; small % of total volume

A.P.E.

atomic number = # of protons = # of electrons

M.A.N.

mass = atomic number + # of neutrons

atomic number

# of protons in an element; defines element type

isotopes

atoms of same element, w/ dif. # of neutrons; identified by mass #

isotope (similarities)

chemically + physically; # of protons and electrons

isotope (differences)

# of neutrons; mass

atomic mass

weighted average of mass of isotopes of that element; expressed in amu (atomic mass number); usually not a whole number

atomic mass (equation)

(mass₁ * (abundance%₁) + (mass₂ * (abundance%₂); add on as many examples provided

nuclear chemistry

study of structure of atomic nuclei and the changes they undergo

nuclear reactions (vs. chem rx)

emit particles +/ rays; atoms converted to dif. element; involve p⁺, n⁰, and e⁻; large energy charges; rx rate not affected by temp, particle size, concentration, +/ catalysts

radioisotopes

isotopes w/ unstable nuclei (too few/many neutrons)

radioactive decay

unstable nuclei losing energy; emit radiation to become stable; spontaneous process; element redefined by new atomic #; types: alpha, beta, and gamma

alpha (α) (radiation)

emission of alpha particle; ⁴₂HE; positive; 4amu; shield: paper/air

beta (β) (radiation)

emission of beta particle (fast moving electron); ⁰-₁e / ⁰-₁β; negative; 1/1837amu (a.k.a. 0amu); shield: foil

gamma (ɣ) (radiation)

high energy electromagnetic radiation; ⁰₀ɣ; neutral; 0amu; shield: concrete

approx. energy (radiation)

high - gamma; medium - beta; low - alpha

penetrating power (radiation)

high - gamma; medium - beta; low - alpha

nuclear stability

when nucleus will not randomly decay

very stable elements

atomic # 1-20; 1:1 proton:neutron ratio

moderately stable elements

atomic # 21-82; 1:1.5 proton:neutron ratio

unstable/radioactive elements

atomic # 82+

transmutation

conversion of an atom of one element into an atom of another element; based on atom’s new atomic # after nuclear rx; discovered by Ernest Rutherford (i think?)

half-life

time it takes for half of a radioisotope’s nuclei to decay into its products; table format: # of half-lives | time | amount/mass

half-life (equation)

mₜ = m₀ * 0.5ⁿ; mₜ = amount/mass remaining, m₀ = initial amount/mass; n = # of half-lives (a.k.a. (= (total time) / (length of 1 half-life)))

nuclear reactions (types)

radioactive decay; nuclear disintegration; fission; fusion

nuclear disintegration

emission of a proton or neutron

fission

splitting of a nucleus (heavy nucleus into 2 approx. = parts); chain rx; can be slowed if controlled by neutron moderator (^ rx rate, ▼ speed) and neutron absorption (control rods to ▼ slow neutrons); not controlled → atomic bomb

fusion

combining of two nuclei (two light nuclei into one heavy); not occur under standard conditions

fusion (advantages)

inexpensive; no radioactive waste

fusion (disadvantages)

requires large amt of energy to start; hard to control

film badge

detects radioactive exposure; for small areas + amts

geiger counter

detects radiation amounts; for large amounts

radiation (uses)

radioactive dating; diagnose diseases; cancer treatment; x-rays; tumor treatment; study chem. rx; food irradiation; power plants; everyday items (ex: lanterns, heart pacemakers, and smoke detectors)