Lattice enthalpy

• Explain why the second ionisation energy of calcium is more endothermic than the first ionisation energy of calcium.


  -Ca+ is smaller than Ca/ proton

  -greater attraction from nucleus
• Suggest why the second electron affinity of oxygen is positive


  -"oxide" ion, O- and electron are both negative

  -hence energy is required to overcome repulsion
• The lattice enthalpies of calcium oxide and magnesium oxide are different. Comment on this difference. In your answer you should make clear how the sizes of the lattice enthalpies are related to any supporting evidence.


  -differences in size of lattice enthalpies linked to ionic sizes/attraction using more/less exothermic rather than bigger or smaller

  -Mg2+ is smaller/Mg2+ has greater charge density

  -hence has stronger attraction for O2-
• Define, using an equation with MgCl2 as an example, what is meant by the term lattice enthalpy


  -Mg2+(g) + 2Cl- (g) → MgCl2(s)

  The enthalpy change that accompanies the formation of one mole of a solid (compound) (1);

  from its constituent gaseous ions
• Explain why the first ionisation energy of calcium is endothermic.


  Ionisation energy refers to removing electrons that are attracted to the nucleus / energy needed to overcome the force of attraction between outer electrons and nucleus
• Explain why the first electron affinity for oxygen is exothermic.


  Electron affinity involves an electron (being gained) experiencing attraction to the nucleus
• The lattice enthalpy for iron(II) oxide is -3920 kJ mol-1 . Suggest a reason for the difference in lattice enthalpy between calcium oxide and iron(II) oxide.


  charge density of Fe2+ greater (than that of Ca2+)
• Which one of the following compounds has the most exothermic lattice enthalpy?

  • calcium bromide

  • calcium chloride

  • potassium bromide

  • potassium chloride

  Explain your answer in terms of the ions present.

  - Calcium chloride

  -Br- has larger ionic radius than Cl -

  -K+ has a lower charge than Ca2+ /

  -Strongest attraction between ions (when smallest radius and highest charge
• Describe how, and explain why, the lattice enthalpy of magnesium fluoride differs from that of calcium chloride.


  -Magnesium fluoride more exothermic than calcium chloride /

  -Ionic radius of Mg2+ is less than that of Ca2+

  -charge density of fluoride ion is greater than that of chloride ion

  -Stronger (electrostatic) attraction between cation and anion in MgF2 than in CaCl2
• Describe how, and explain why, the lattice enthalpy of magnesium fluoride differs from that of calcium chloride


  -For second ionisation energy the electron lost is closer to the nucleus / AW (

  - For second ionisation energy the electron is lost from a particle that is already positive (1); For second ionisation energy there is one more proton than electron (1) So outer electron more firmly attracted to the nucleus (
• The first ionisation energy for sodium is more endothermic than of potassium

  Na has fewer shells

  Greater nuclear attraction
• The lattice enthalpy or sodium oxide is more exothermic than of potassium oxide

  Na+ is smaller

  Na+ has a stronger attraction to O2-
• enthalpy change of atomisation of iodine

  1/2 I2 (s) --> I (g)
• electron affinity

  gain in electrons
• ionisation energy

  loss in electrons
• enthalpy change of atomisation

  endothermic due to bond breaking
• bond enthalpy

  reactant - product
• successive ionisation energy

  energy required to remove each electron intern

  predict:

  electron in outer shell

  group and identity
• enthalpy change of solution equation

  solution = -formation + hydration
• trend in lattice enthalpyincrease in ionic charge of gaseous ions

  higher charge (e.g. Ca2+ > Na+)

  = more energy released when ionic lattice forms

  * due to stronger electrostatic forces

  = more exothermic lattice enthalpy
• trend in lattice enthalpydecrease in ionic radius of gaseous ions


  smaller ionic radius

  = higher charge density + ions are CLOSER TOGETHER

  = stronger ionic attraction

  = more exothermic lattice enthalpy
• describe dissolving a solid ionic lattice

  electrostatic attraction between ions break to form gaseous ions

  (endothermic)

  hydrogen bonds form between water and gaseous ions (exothermic)
• WHY do ionic lattices dissolve in water?

  oxygen is more electronegative than hydrogen

  this draws electrons towards the oxygen atom

  creates a DIPOLE
• how does cis-platin function?

  2 Cl- ion ligands are easy to displace:

  * Cis-platin loses 2 Cl- ions

  * Replaces with 2 nitrogen atoms on DNA molecules inside cancerous cells

  This blocks the DNA, preventing cancerous cell dividing and reproducing:

  * Causes cell to die

  * Cannot repair DNA damage
• cis-platin disadvantages

  However, cis-platin prevents normal cells from reproducing

  e.g. blood cells

  = suppresses immune system

  = higher infection risk

  Damages cells in kidneys