Ionisation

• What is the definition of ionisation energy?

  The energy to remove one mole of electrons
• What does the first ionisation energy involve?

  Removing electrons from gaseous atoms
• What is the equation for the first ionisation energy?

  $X(g) \rightarrow X^+$$(g) +$$e^-$
• What is the second ionisation energy?

  Energy to remove electrons from 1+ ions
• How does ionisation energy change across successive ionisations?

  It increases due to positive ion charge
• What are the three main factors affecting ionisation energy?

  • Nuclear charge
  • Distance from the nucleus (atomic radius)
  • Electron shielding
• How does nuclear charge affect ionisation energy?

  Higher nuclear charge increases electron attraction
• How does atomic radius affect ionisation energy?

  Larger atomic radius reduces electron attraction
• How does electron shielding affect ionisation energy?

  Inner electrons repel outer electrons, lowering attraction
• Why is there a sharp increase in ionisation energy when an electron is removed from a lower energy shell?

  Inner shell electrons are more strongly attracted
• What is the trend in first ionisation energy across a period?

  It increases due to higher nuclear charge
• Why is there a dip in ionisation energy between Group 2 and Group 3 elements?

  Group 3 outer electron is in a higher-energy p orbital
• Why is there a dip in ionisation energy between Group 5 and Group 6 elements?

  Group 6 has paired electrons causing repulsion
• What is the trend in first ionisation energy down a group?

  It decreases due to increased atomic radius
• Why does helium have the highest first ionisation energy?

  Helium has a small radius and high nuclear charge
• Why does francium have the lowest first ionisation energy?

  Francium has a large radius and significant shielding
• Why do noble gases have higher first ionisation energies compared to other elements?

  Noble gases have full outer electron shells
• How does ionisation energy provide evidence for electron shells?

  Successive ionisation energies show distinct energy levels
• How does ionisation energy explain the reactivity of Group 1 metals?

  Low ionisation energies make them highly reactive
• Why is the first ionisation energy of aluminium lower than magnesium?

  Aluminium's outer electron is in a higher-energy p orbital
• Why is the first ionisation energy of sulfur lower than phosphorus?

  Sulfur's outer electron is paired, causing repulsion
• Why does the first ionisation energy of oxygen dip compared to nitrogen?

  Oxygen has a paired electron causing repulsion
• Why do transition metals have similar first ionisation energies across the period?

  Electrons in 3d subshell provide shielding
• Why is the second ionisation energy of sodium much higher than the first?

  Remaining electron is in a lower-energy inner orbital
• What equation links ionisation energy to the energy of a photon?

  $E =$$h \cdot \nu$
• What is Planck's constant?

  6.63 \times 10^{-34} \text{ J·s}
• How do you calculate the wavelength of a photon from its ionisation energy?

  Use $E =$$\frac{h \cdot c}{\lambda}$
• What is the speed of light?

  $3.00 \times 10^{8} \text{ m/s}$
• How is ionisation energy typically measured and expressed?

  Measured in kilojoules per mole (kJ/mol)
• How do you convert ionisation energy from joules to kilojoules per mole?

  Multiply by Avogadro’s constant, then divide by 1000
• Calculate the ionisation energy of a photon with frequency $5.0 \times 10^{15} \text{ Hz}$.


  $199.7 \text{ kJ/mol}$
• Calculate the energy required to ionise a single helium atom with first ionisation energy $2370 \text{ kJ/mol}$.


  $3.94 \times 10^{-18} \text{ J/atom}$
• How does successive ionisation energy data help determine the group of an element?

  Large jumps indicate removal from lower energy shells