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4E: Atoms, Nuclear Decay, Electronic Structure, and Atomic Chemical Behavior

Inside the atom and across the table: decay curves, orbitals filling by rule, periodic trends drawn as height, and the stoichiometry that counts it all.

16 topics · 70 questions

Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.

4E. Atomic Number, Atomic Weight, and Isotopes

  1. How it worksHow do protons lock in the identity of an element while neutrons only tune its mass?
  2. Worked exampleFind the atomic weight of chlorine given 75 percent chlorine-35 and 25 percent chlorine-37.
  3. Common mistakeWhy isn't the atomic weight printed on the periodic table the mass of any real single atom?
  4. Going furtherWhat happens to an isotope's value as a medical tracer when its half-life is far too long?
Your turneasy1 of 3
An element occurs as two isotopes: 66 percent of its atoms have mass 49 u and the rest have mass 88 u. Find its atomic weight, in u.

4E. Nuclear Forces, Mass Defect, and Binding Energy

  1. How it worksHow does the strong force overpower electrostatic repulsion but only across a tiny distance?
  2. How it worksHow does the binding energy per nucleon climb to a peak at iron and fall away on both sides?
  3. Worked exampleFind the energy released when a mass defect of 0.030 atomic mass units shows up in a nucleus.
  4. Common mistakeWhy isn't a heavier nucleus automatically a more tightly bound one?
Your turnmedium1 of 3
A nucleus forms with a mass defect of 66 thousandths of an atomic mass unit. Find the binding energy, in MeV, using 931.5 MeV per atomic mass unit.

4E. Alpha, Beta, and Gamma Decay

  1. How it worksHow does alpha decay peel off two protons and two neutrons and slide the element two boxes left?
  2. How it worksHow does beta minus decay flip a neutron into a proton and nudge the atomic number up by one?
  3. Worked exampleFind the daughter nucleus produced when uranium-238 throws off an alpha particle.
  4. Worked exampleFind what carbon-14 becomes after it undergoes beta minus decay.
  5. Common mistakeWhy isn't a gamma ray emission changing which element you are holding?
Your turnmedium1 of 3
A nucleus of atomic number 92 undergoes 4 alpha decays and 6 beta-minus decays. Find the atomic number of the final product.

4E. Half-Life, Exponential Decay, and Semi-Log Plots

  1. How it worksHow does a fixed fraction decaying per unit time carve out a curve that halves over and over?
  2. Worked exampleFind how much of an 80 mg technetium-99m dose survives 18 hours at a 6 hour half-life.
  3. How it worksHow does putting the count on a logarithmic axis straighten an exponential decay into a line?
  4. Worked exampleFind the half-life of a sample that falls from 800 to 100 counts per minute in 30 minutes.
  5. Going furtherWhat happens to the slope of a semi-log decay plot when an isotope decays twice as fast?
Your turneasy1 of 3
A 151 mg dose of a radioisotope has a half-life of 8 hours. Find the mass remaining, in mg, after 6 of those half-lives have elapsed.

4E. The Mass Spectrometer and Mass Spectra

  1. How it worksHow does a magnetic field curve a light ion more sharply than a heavy one moving just as fast?
  2. Worked exampleShow me why a compound holding one bromine gives two molecular ion peaks of nearly equal height.
  3. Common mistakeWhy isn't the tallest peak in a mass spectrum always the intact molecule?
Your turnhard1 of 3
In a mass spectrometer run at fixed accelerating voltage and field, the path radius of a singly charged ion goes as the square root of its mass. An ion of mass 48 u follows a radius of 23 cm. Write the radius, in cm, of an ion of mass x u.

4E. The Bohr Atom, Ground and Excited States, and Line Spectra

  1. How it worksHow does an electron falling between two fixed rungs release a photon of one exact energy?
  2. How it worksHow do absorption and emission spectra end up as photographic negatives of one another?
  3. Worked exampleFind the energy of the photon hydrogen emits dropping from level three to level two.
  4. Common mistakeWhy isn't the Bohr model's orbiting electron a picture of where an electron truly sits?
  5. Going furtherWhat happens to the gaps between energy levels as the electron climbs toward ionization?
Your turnmedium1 of 3
A hydrogen electron drops from level 6 to level 2. Find the energy of the emitted photon, in eV, using an energy of -13.6/n2 eV for level n.

4E. Orbitals, Quantum Numbers, and Electrons per Orbital

  1. How it worksHow do four quantum numbers name a shell, a shape, an orientation and a spin for one electron?
  2. How it worksHow do s, p and d orbitals take on their sphere, dumbbell and cloverleaf shapes?
  3. Worked exampleFind how many electrons the third shell holds and how they divide across its subshells.
  4. Common mistakeWhy isn't an orbital a track that the electron runs around on?
Your turneasy1 of 3
Find the greatest number of electrons that the shell with principal quantum number n = 4 can hold.

4E. Electron Configuration, the Pauli Principle, and Magnetism

  1. How it worksHow does the aufbau order fill orbitals one electron at a time from lowest energy upward?
  2. Worked exampleShow me the ground state electron configuration of iron written out subshell by subshell.
  3. How it worksHow do unpaired electrons make an atom paramagnetic and drag it toward a magnet?
  4. Worked exampleFind the configuration of the iron three plus cation and which electrons depart first.
  5. Common mistakeWhy isn't chromium's configuration the one the standard filling order predicts?
Your turnhard1 of 3
A transition metal ion has 7 electrons in its 3d subshell and no other partly filled subshell. Applying Hund's rule, find the number of unpaired electrons.

4E. Effective Nuclear Charge and Shielding

  1. How it worksHow do inner shells screen the nucleus and leave a valence electron only a reduced pull?
  2. Worked exampleFind the effective nuclear charge felt by a valence electron of oxygen with a simple core count.
  3. Common mistakeWhy isn't the pull on a valence electron weakening as you move rightward across a row?
  4. Going furtherWhat happens to that reduced pull when an entire new shell is added going down a column?
Your turneasy1 of 3
A neutral atom has atomic number 16 and 7 inner-shell electrons. Estimate the effective nuclear charge felt by one of its valence electrons, counting only the core as shielding.

4E. The Photoelectric Effect and the Heisenberg Uncertainty Principle

  1. How it worksHow does a single photon hand its entire energy to one electron and either free it or fail?
  2. Worked exampleFind the kinetic energy of an electron ejected by 5.0 eV photons from a metal of work function 3.5 eV.
  3. Common mistakeWhy isn't a brighter beam able to eject electrons that its frequency alone could not?
  4. Going furtherWhat happens to how well an electron's position is known as its momentum is pinned down harder?
Your turneasy1 of 3
Photons of energy 10 eV strike a metal whose work function is 3 eV. Find the maximum kinetic energy of the ejected electrons, in eV.

4E. Classifying Elements into Groups by Electronic Structure

  1. How it worksHow does the count of valence electrons sort the table into alkali metals, halogens and noble gases?
  2. How it worksHow does a partly filled d subshell hand transition metals their many oxidation states?
  3. Common mistakeWhy isn't hydrogen an alkali metal even though it perches on top of that column?
  4. Worked exampleFind which family an element belongs to from a valence configuration of 3s2 3p5.
Your turneasy1 of 3
An element has the valence configuration 4s2 4p5. Which family does it belong to?

4E. Atomic and Ionic Size and Ionization Energy

  1. How it worksHow does a climbing nuclear pull reel the same shell in tighter with every step across a period?
  2. How it worksHow does ionization energy rise across a row and drop down a column in mirror image to size?
  3. Worked exampleFind which of sodium, magnesium and aluminum demands the most energy to lose one electron.
  4. Common mistakeWhy isn't sodium's second ionization energy only a little larger than its first?
  5. Going furtherWhat happens to an atom's radius when it loses an electron, and when it captures one?
Your turnhard1 of 3
An element has 5 valence electrons outside a noble-gas core. Find how many electrons can be stripped away before the next ionization energy jumps by an enormous step.

4E. Electron Affinity and Electronegativity

  1. How it worksHow does electronegativity rate a tug inside a bond while electron affinity rates a lone atom?
  2. Worked exampleFind which of H-F, H-Cl and H-Br is the most polar bond and which atom carries the minus end.
  3. Common mistakeWhy isn't the noble gas column the peak of electronegativity despite sitting farthest right?
  4. Ties togetherHow do the same periodic trends that set electronegativity decide whether a bond turns out ionic?
Your turneasy1 of 3
Hydrogen (electronegativity 2.1) bonds in turn to fluorine (4.0), chlorine (3.0) and bromine (28 tenths of a Pauling unit). Which bond is the most polar, and which atom carries the partial negative charge?

4E. Moles, Molecular Weight, Percent Composition, and Formulas

  1. How it worksHow does Avogadro's number convert a reading on a balance into a population of particles?
  2. Worked exampleFind the mass of 0.25 moles of calcium carbonate using a periodic table.
  3. How it worksHow does percent composition turn into an empirical formula by dividing through by the smallest?
  4. Worked exampleFind the empirical formula of a compound that is 40 percent carbon, 6.7 hydrogen and 53.3 oxygen.
  5. Common mistakeWhy isn't an empirical formula the same thing as a molecular formula?
Your turneasy1 of 3
Find the number of moles in 642 grams of calcium carbonate, whose molar mass is 100 g/mol.

4E. Balancing Equations, Limiting Reactant, and Theoretical Yield

  1. How it worksHow does balancing an equation force the same atom count onto both sides of the arrow?
  2. How it worksHow does the mole ratio in a balanced equation convert reactant moles into product moles?
  3. Worked exampleFind the limiting reactant when 4.0 moles of hydrogen meet 3.0 moles of oxygen to make water.
  4. Worked exampleFind the percent yield when a reaction with a theoretical yield of 25 g actually delivers 18 g.
  5. Common mistakeWhy isn't the reactant with the smaller mass always the one that runs out first?
Your turnhard1 of 3
In the reaction 2 H2 + O2 → 2 H2O, 9 mol of hydrogen is mixed with 6 mol of oxygen. Find the greatest number of moles of water that can form.

4E. Oxidation Numbers, Redox Agents, and Disproportionation

  1. How it worksHow do the oxidation number rules walk through a compound atom by atom to one consistent answer?
  2. Worked exampleFind the oxidation state of manganese inside the permanganate ion.
  3. Common mistakeWhy isn't the oxidizing agent the species that ends up oxidized?
  4. Ties togetherHow does the electron bookkeeping that balances a redox equation also fix the direction of a galvanic cell?
Your turnmedium1 of 3
A polyatomic ion has the formula XO3 and carries a charge of 2 minus. Find the oxidation state of X.

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