Many-Electron Atoms: Spin, Antisymmetry and Effective Charge · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Many electrons, screened pulls, strict rules

Science · Chemistry · ages 18-20
Name ______________________   Date ____________

  1. How does the familiar orbital filling rule follow from antisymmetry?

    • Electrons must stay as far apart as possible
    • Every orbital holds at most one electron
    • No two electrons share all four quantum numbers

  2. Why does the 4s orbital fill before 3d in a neutral atom?

    • Penetration gives 4s an inner lobe near the nucleus
    • The 4s orbital is simply smaller than 3d
    • Electrons always fill in strict n order

  3. Core electrons shield the nucleus well, while electrons in the same shell shield poorly.

    Circle one:   True   False

  4. Potassium loses its first electron. Which one leaves?

    • A 4s electron
    • A 3d electron
    • Either, since they fill together

  5. Moving across a row, the effective charge climbs. What happens to atomic size?

    • The atom gets smaller
    • The atom gets larger
    • The atom keeps the same size

  6. Why does the first ionisation energy generally rise across a row?

    • New shells pile on outside the core
    • Penetration fades down every group
    • The growing effective charge grips harder

  7. Magnesium ends in 3s squared and aluminium in 3s squared 3p to the one. Which has the lower first ionisation energy?

    • Aluminium, since its 3p electron is screened and less penetrating
    • Magnesium, since it holds more electrons overall
    • Neither, since neighbours always tie

  8. A student says 3d must fill before 4s because 3 is smaller than 4. What is the error?

    • The 3 in 3d is smaller than the 4 in 4s
    • Penetration decides the order, not the n label alone
    • d orbitals always fill before s orbitals
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Many electrons, screened pulls, strict rules W1-mt_WPesw2f8T3-s1

  1. No two electrons share all four quantum numbers · Antisymmetry wears work clothes as the familiar filling rule.
  2. Penetration gives 4s an inner lobe near the nucleus · That inner lobe feels extra pull that the buried 3d misses.
  3. True · Poor same shell shielding is why the pull climbs across a row.
  4. A 4s electron · Building the atom drops 3d below 4s, stranding 4s on top.
  5. The atom gets smaller · A climbing effective charge reels the outer electrons inward.
  6. The growing effective charge grips harder · More pull on the outer electron means a costlier removal.
  7. Aluminium, since its 3p electron is screened and less penetrating · A new subshell electron feels less pull and leaves more cheaply.
  8. Penetration decides the order, not the n label alone · Inner lobes beat bare n labels in the filling race.
Worksheet · LightMySky