Trends Across Period 3: Radius, Ionisation Energy and Melting Point · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading the third row

Science · Chemistry · ages 16-17
Name ______________________   Date ____________

  1. Which element towers in melting point, and why?

    • Argon, with strong bonds
    • Silicon, with a giant covalent lattice
    • Sodium, as a metal

  2. Why do atoms shrink across period 3?

    • More protons pull the same shell harder
    • Electrons leave the atom
    • Shells are lost along the row

  3. Phosphorus melts near 44 C because it is a giant lattice.

    Circle one:   True   False

  4. Why does first ionisation energy dip from phosphorus to sulfur?

    • Pairing repulsion in a shared orbital frees one electron
    • A new shell starts
    • Sulfur holds fewer protons

  5. Why does first ionisation energy dip from magnesium to aluminium?

    • Aluminium holds fewer protons
    • A new shell starts
    • The aluminium outer electron sits in a higher 3p orbital

  6. Why does silicon melt near 1400 C while phosphorus melts near 44 C?

    • Higher nuclear charge in silicon
    • Strong lattice bonds versus weak forces between molecules
    • More electrons in silicon

  7. A student says melting rises steadily with nuclear charge to argon. What is wrong?

    • Melting follows structure, so it crashes after silicon
    • Ionisation never rises
    • Silicon melts lower than sodium

  8. An unknown period 3 element melts low yet ionises high. Where does it sit?

    • Left side, with the metals
    • At silicon
    • Right side, among the small molecules
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Answer key

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

Reading the third row W1-mt_stFFQ6GPIh-s1

  1. Silicon, with a giant covalent lattice · Its lattice locks every atom in strong bonds.
  2. More protons pull the same shell harder · Same shell plus bigger charge means smaller atoms.
  3. False · Phosphorus is small molecules held by weak forces.
  4. Pairing repulsion in a shared orbital frees one electron · The first pair repels, so one partner leaves easily.
  5. The aluminium outer electron sits in a higher 3p orbital · Higher and further out beats the extra proton.
  6. Strong lattice bonds versus weak forces between molecules · Melting follows structure, not charge.
  7. Melting follows structure, so it crashes after silicon · Charge climbs on, but structure switches to molecules.
  8. Right side, among the small molecules · Low melting says molecules, high ionisation says right side.
Worksheet · LightMySky