Chemical energetics (Section 2 of 2)

What does Lattice enthalpy depend upon?

• Charge of the ions: As the charge increases the lattice enthalpy becomes more exothermic For Example: Lattice enthalpies of  (Mg has a 2+ charge while Li has a 1+ charge)
• MgO.......-1050 KJ/mol
• LiO.........- 3923 KJ/mol
• Size of the ions: the lattice enthalpy becomes less exothermic as the size of the ion decreases, because as the size increases the the attraction between the two oppositely charged ions decreases as both their centres of charge are further away from each other

Stabilities of Group II carbonates:

The trend: The carbonates get more and more stable as we move down the group because down the group polarization power of the cation decreases

What is polarization?

The tendency for an ion to reshape (or redistribution of charge) due to external electric fields is termed polarization.

How does polarization affect the stabilities of group II carbonates?

As we move down a group the size of the ion increases  hence the charge density decreases which thus causes a decrease in polarizing power of the cation and when this happens the Carbonates becomes more stable as we go down the group and hence their decomposition temperatures increase down the group.

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