Unit 3: The Atom

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Democritus (discovery)

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Democritus (discovery)

matter made of ‘atomas’; not divisible

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John Dalton (discovery)

Dalton's theory

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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)

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JJ Thomson (experiment)

cathode ray experiment

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JJ Thomson (discovery)

discovered electron; plum pudding model

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Millikan (experiment)

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

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Millikan (discovery)

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

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Ernest Rutherford (experiment)

gold foil experiment

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Ernest Rutherford (discovery)

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

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James Chadwick (discovery)

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

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Niels Bohr (discovery)

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

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electron (discoverer/location/charge/symbol)

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

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proton (discoverer/location/charge/symbol)

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

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neutron (discoverer/location/charge/symbol)

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

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nucleus

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

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A.P.E.

atomic number = # of protons = # of electrons

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M.A.N.

mass = atomic number + # of neutrons

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atomic number

of protons in an element; defines element type

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isotopes

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

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isotope (similarities)

chemically + physically; # of protons and electrons

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isotope (differences)

of neutrons; mass

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atomic mass

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

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atomic mass (equation)

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

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nuclear chemistry

study of structure of atomic nuclei and the changes they undergo

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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

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radioisotopes

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

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radioactive decay

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

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alpha (α) (radiation)

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

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beta (β) (radiation)

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

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gamma (ɣ) (radiation)

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

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approx. energy (radiation)

high - gamma; medium - beta; low - alpha

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penetrating power (radiation)

high - gamma; medium - beta; low - alpha

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nuclear stability

when nucleus will not randomly decay

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very stable elements

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

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moderately stable elements

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

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unstable/radioactive elements

atomic # 82+

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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?)

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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

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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)))

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nuclear reactions (types)

radioactive decay; nuclear disintegration; fission; fusion

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nuclear disintegration

emission of a proton or neutron

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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

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fusion

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

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fusion (advantages)

inexpensive; no radioactive waste

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fusion (disadvantages)

requires large amt of energy to start; hard to control

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film badge

detects radioactive exposure; for small areas + amts

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geiger counter

detects radiation amounts; for large amounts

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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)

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