What is an ionic bond?
A strong electrostatic attraction between oppositely charged ions
What are the units are ionic radius measured in?
Nanometres nm
Why are cations smaller than the atoms they come from?
Loss of electrons may result in loss of outer shell
More positive protons so electrons will be pulled in more
Why are anions larger than the atoms they come from?
Gain of electrons so electrons > protons
Electrons repel each other, held less strongly
What happens to the ionic radius as a group is descended?
Increases
Why does the ionic radius increase down a group (3 things)?
More protons BUT
More shielding by complete inner shells of electrons so less attraction of e to p
Outer shell further away from nucleus
What are isoelectronic ions?
Ions with same no of electrons/electron configurations
What is the trend in ionic radius for a set of isoelectronic ions (eg N3- to Al3+)?
decreases from highest charge anions to highest charge cations
Why does ionic radius decrease across a set of isoelectronic ions?
No of protons in nucleus of ion increases, electrons pulled in more closely to nucleus
What happens to the ionic radius across a period?
Decreases
Why does the ionic radius decrease along a period (3 things)?
No of electrons stays same but atomic number increases, electrons pulled in more strongly
What 2 things does the strength of the ionic bond depend on?
Ionic charge
Ionic radius
Why does a greater ionic charge mean a stronger ionic bond?
Bigger charges exert greater attractive forces between each other
Why does a smaller ionic radius mean a stronger ionic bond (4 things)?
Smaller ions, more closely packed together in ionic lattice, shorter distance between oppositely charged ions, stronger electrostatic forces between them
What are 4 typical physical properties of ionic compounds?
High melting points
Hard and brittle structure
Poor electrical conductivity when solid but good when molten/in solution
Often soluble in water
What process provides evidence for the migration of ions?
Electrolysis
Why do ionic solids have high melting points?
Strong electrostatic attractions between oppositely charged ions so takes lot of heat energy to overcome
What 2 things does the melting point of an ionic solid depend on?
Number of charges on ions
Sizes of ions
Why are ionic solids brittle?
A small displacement shifts ion layers slightly, ions of same charge are brought side by side so structure repels itself to pieces/shatters
Why do ionic compounds usually dissolve in water?
Positive ions attracted to lone pairs on water molecules and dative covalent bonds may form, water molecules form hydrogen bonds with negative ions
What does the solubility of an ionic compound in water depend on?
Whether there are big enough attractions between water molecules and ions to overcome attractions between ions themselves
How can a molten ionic compound conduct electricity (4 things)?
Cations move towards cathode, each ion picks up electrons, movement of these electrons leaves spaces on cathode
Power source moves electrons along wire in external circuit to fill those spaces creating flow of electrons (electrical current)
Anions lose electrons to anode
Electrons deposited on anode pumped off around external circuit by power source, ending up on cathode and transferred to cations
