2.2 : Electrons, bonding and structure - ionic bonding Flashcards
Define an ionic bond
An ionic bond is the electrostatic attraction between oppositely charged ions.
Describe the structure of a giant ionic lattice
In a giant ionic lattice:
- each ion is surrounded by oppositely charged ions in a regular arrangement
- these ions attract each other from all directions
Why do ionic compounds have high melting and boiling points?
The strong electrostatic attractions between the oppositely charged ions in the solid lattice requires a lot of energy to overcome.
Why can ionic compounds conduct when molten/dissolved but not when solid?
In a solid ionic lattice, the ions are held in fixed positions and cannot move so it does not conduct electricity.
When an ionic compound is melted/dissolved in water, the solid lattice breaks down and the ions become free to move so can carry charge through the structure, therefore can conduct electricity.
Are ionic lattices soluble?
Ionic lattices are soluble in polar solvents, like water. Polar water molecules break down ionic lattices by surrounding each ion to form a solution. The slight charges within the polar substance are able to attract the charged ions in the giant ionic lattice. This means the lattice is disrupted and ions are pulled out of it.
What happens when sodium chloride is dissolved in water?
- The giant ionic lattice breaks down.
- The individual ions are surrounded by water molecules with positive ions attracting the slightly negative O and negative ions attracting the slightly positive H of water molecules.
Why is the melting point of MgO higher than the melting point on NaCl?
- The charges on the Mg2+ and O2- ions are greater than those on Na+ and Cl-. – The greater the charge, the stronger the electrostatic forces between the ions.
- This means that more energy is required to break up the ionic lattice, so the melting point of MgO is higher.
