Atomic Models
This subatomic particle carries a positive charge, resides in the central nucleus, and uniquely determines the atomic number and chemical identity of an element
What is a proton?
Atoms of the exact same element that contain equal numbers of protons but different numbers of neutrons (giving them different mass numbers)
What are isotopes?
The constant amount of time required for exactly 50% of the radioactive parent atoms in a sample to decay into stable daughter isotopes
What is a half-life?
The high-energy nuclear process in which two light atomic nuclei combine to form a heavier element
What is nuclear fusion?
Outermost energy level (n) electrons that dictate an element's chemical reactivity, bonding preferences, and ion formation
What are valence electrons?
J.J. Thomson used this experimental vacuum tube apparatus to show that cathode rays were deflected by electrical fields, proving the existence of negatively charged electrons
What is a cathode ray tube?
Complete this balanced nuclear decay equation by providing the symbol for the particle emitted when Carbon-14 decays into Nitrogen-14
What is a beta particle / electron?
An 80.0-gram sample of Cobalt-60 (t1/2 = 5.27 years) decays for 15.81 years (3 half-lives). Calculate the remaining mass of active Cobalt-60
What is 10.0 grams?
Identify the primary product nucleus formed in the Sun's core when four Hydrogen-1 nuclei fuse together in the proton-proton chain
What is Helium-4?
State the directional trend for Atomic Radius across a period (left-to-right) and down a group (top-to-bottom)
Decreases across a period (left-to-right); Increases down a group (top-to-bottom)
Ernest Rutherford fired alpha particles at a thin gold foil; explain how the unexpected wide-angle deflections provided empirical evidence for a small, dense, positively charged nucleus surrounded by mostly empty space
What is the Gold Foil Experiment?
Using the Band of Stability, explain why a neutron-rich nucleus above the band undergoes beta-minus decay while a proton-rich nucleus below the band undergoes positron emission
Level 4
Neutron-rich isotopes undergo beta decay to convert a neutron into a proton, lowering N/Z. Proton-rich isotopes undergo beta + emission to convert a proton into a neutron, raising N/Z toward the stable band
An ancient charcoal artifact discovered at an archaeological site contains 12.5% (1/8) of its original Carbon-14 (t1/2 = 5,730 years). Calculate the age of the charcoal in years
What is 17,190 years?
Explain why fusing light elements up to Iron-56 releases massive net energy (exothermic), while attempting to fuse Iron-56 absorbs energy (endothermic), referencing the binding energy per nucleon curve
Iron-56 sits at the maximum peak of binding energy per nucleon (8.79 MeV/nucleon). Fusing light nuclei up to Iron increases stability and releases mass defect energy. Fusing Iron-56 requires net energy input because the resulting heavier nucleus is less tightly bound
Calculate Effective Nuclear Charge (Zeff = Z - S$) for Sodium (Z=11) and Chlorine (Z=17), and explain why Chlorine has a smaller atomic radius than Sodium
Sodium Zeff = 11 - 10 = +1; Chlorine Zeff = 17 - 10 = +7. Chlorine's net +7 nuclear charge pulls its 3rd shell electrons much closer than Sodium's +1 pull, making Chlorine smaller
Niels Bohr analyzed this experimental optical data—showing discrete colored lines rather than a continuous rainbow—to prove that electrons inhabit quantized principal energy levels (n)
Level 4
What is an atomic emission spectrum?
Write the complete balanced nuclear reaction for Radium-226 undergoing alpha decay.
What is Radon-222?
In nuclear medicine, a radioisotope has a physical half-life (tphys) of 6.0 hours and a biological clearance half-life (tbio) of 24.0 hours. Calculate its effective half-life (teff) in the patient's body?
What is 4.80 hours?
According to Einstein's mass-energy equivalence, explain where the energy released during fusion comes from and compare its magnitude to chemical combustion
Level 4
Fusion energy originates from the mass defect—missing nuclear mass converted into energy. Nuclear fusion releases millions of times more energy per kilogram than chemical bond rearrangement
Explain why a neutral Sodium atom (Na) shrinks dramatically when it loses its 1 valence electron to become a Sodium cation (Na+), referring to energy levels (n) and nuclear pull
Losing its 1 valence electron empties the entire outer n=3 shell. The remaining 10 core electrons in n=2 are pulled inward by 11 protons (Zeff = +11 - 2 = +9), shrinking Na+ significantly
Contrast J.J. Thomson’s "plum pudding" model with Rutherford’s nuclear model, and justify why discrete spectral lines required shifting from Rutherford's planetary picture to Bohr's quantized energy level model
Level 4
Thomson's model assumed uniform positive sphere charge; Rutherford proved positive charge is concentrated in a tiny nucleus. Bohr added quantized energy levels (n) to explain why orbiting electrons don't collapse into the nucleus and why excited atoms emit specific line spectra
On the nuclear binding energy curve, explain why light isotopes (A < 56) release energy through nuclear fusion, whereas massive unstable isotopes (A > 200) release energy through nuclear fission or alpha decay to reach greater stability
Level 4
Fusing light nuclei (A < 56) increases binding energy per nucleon toward the Iron-56 peak, converting mass defect into released energy. Fissioning heavy nuclei (A > 200) splits massive unstable cores into tighter mid-sized fragments closer to Iron-56, also releasing nuclear energy
Using the decay constant equation, compare the immediate radiation intensity and long-term environmental risk of Cesium-137 (t1/2 = 30.17 yr) versus Iodine-129 (t1/2 = 15.7M yr)
Level 4
Cesium-137 has a short half-life, yielding a large decay constant and intense short-term radioactivity/heat. Iodine-129 has a tiny decay constant and low immediate emissions per second, but remains an environmental contaminant for millions of years.
Contrast quiet main-sequence stellar nucleosynthesis (onion-shell fusion up to Iron-56) with explosive supernova nucleosynthesis that builds heavy elements like Gold and Uranium
Level 4
Main-sequence stars undergo quiet core fusion building elements up to Iron-56 where exothermic fusion ends. When massive stars suffer core collapse, the extreme energy and neutron flux of a supernova explosion force endothermic fusion to synthesize elements heavier than iron (A > 56), like Gold and Uranium
Analyze this successive ionization energy dataset for a Period 3 element (IE 1 = 738, IE 2 = 1451, IE 3 = 7733, IE 4 = 10540 kJ/mol): identify the location of the core-electron jump, state the number of valence electrons, and deduce the element's exact identity
Level 4
The dramatic jump occurs between IE 2 (1,451 kJ/mol) and IE 3 (7,733 kJ/mol). This proves the element has 2 valence electrons. In Period 3, Group 2, the element is Magnesium (Mg)