Olive StudySmarter OriginalsĪs you can see, not all cations have the same polarising power. Instead, some electrons become clustered between the cation and the anion- a little bit like a shared pair of electrons in a covalent bond.Ĭovalent character and polarisation. The anion becomes polarised because its electrons are no longer evenly distributed in the orbitals. This attraction makes the electrons on the anion overlap the electron cloud of the cation and distorts the anion’s electron density (shown below).Ĭovalent character. The anion (negative ion) then becomes polarised.Įssentially, a cation (positive ion) attracts the electrons on an anion (negative ion). This happens when there is not enough electronegativitybetween the atoms for a complete electron transfer. They also take into account the geometry of the lattice and the distance between the atoms.Ī covalent character means that the electrons in an ionic bond behave a little like those in a covalent bond. In other words, they consider the ions as point charges that bond together to make a lattice. This is based on the assumption that the substance is highly ionic with only electrostatic attraction between the ions. Physicists use a theoretical method to calculate lattice enthalpies. uk Theoretical values for lattice enthalpy Lattice enthalpies get smaller as you go down a group. As their positive ions get bigger, the lattice enthalpies of their chloride salts decrease. You can observe this effect as you go down a group on the periodic table. Ions with larger radii tend to have smaller lattice enthalpies, because the electrostatic attraction between larger ions is weaker. The strength of ionic attraction depends on the closeness of the centres of the attracted ions, so there is a stronger attraction between the magnesium and oxygen ions. This means the ions in the magnesium oxide lattice are closer together.
Magnesium ions and oxide ions are smaller than sodium and chloride ions. So the lattice dissociation enthalpy of magnesium oxide (MgO) is larger than that of sodium chloride (NaCl). More energy is needed to overcome the attraction between the ions and break up the lattice. Ions with larger ionic charges have stronger electrostatic attraction between the ions. Magnesium and oxygen ions have larger ionic charges than sodium and chloride ions. The ions of sodium chloride and magnesium oxide. Can you see a reason for the difference in their lattice enthalpies? Lattice enthalpies of magnesium oxide and sodium chloride. Their crystal lattices have the same geometry, so why are their enthalpies different? Reaction Quotient and Le Chatelier's PrincipleĬompare the lattice enthalpies of sodium chloride and magnesium oxide below.Elemental Composition of Pure Substances.Application of Le Chatelier's Principle.Intramolecular Force and Potential Energy.Variable Oxidation State of Transition Elements.Transition Metal Ions in Aqueous Solution.
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