1. IONIC VS. COVALENT COMPOUNDS

2. IONIC COMPOUNDS COVALENT COMPOUNDS Formed of metal+ nonmetal.
Ions are held in a lattice that grows in all directions.
Formed of nonmetal+nonmetal.
Molecules are also held in a lattice that grows in all directions.
Crystal of NaCl
Crystal of ice

3. IONIC COMPOUNDS COVALENT COMPOUNDS Forces between ions are strong.
Have high melting and boiling points.
The forces between molecules are weak.
Have low melting and boiling points.
compound
Melting point/°C
Boiling point/°C
NaCl
801
1413
MgO
2852
3600 CO
-199
-191
C6H14
-95 69
Explain why MgO has a higher mp than NaCL.

4. COVALENT COMPOUNDS IONIC COMPOUNDS Usually soluble in water.
Conduct electricity when melted or dissolved in water.
Tend to be insoluble in water.
Do not conduct electricity.

5. GIANT COVALENT STRUCTURES

6. Not all covalent solids are molecular!
What do you notice in the following table?
Substance
Melting point/°C
H2O P4 44 S8
115
SiO2 (Silica or quartz)
1710
Diamond (C)
3550
The 1st 3 are molecular /low melting points. Diamond and silica are different.

7. Diamond and Silica are NOT molecular solids with weak lattices!
They are GIANT COVALENT /NETWORK STRUCTURES or MACROMOLECULES.

10. GRAPHITE (C) DIAMOND (C)
A carbon forms strong covalent bond to 3 others. This gives rings of six atoms. The rings form flat layers held together by weak forces.
A carbon forms strong covalent bond to 4 others.
Billions of C atoms are bonded to together in a giant covalent structure.

11. GRAPHITE (C) DIAMOND (C)
Since the layers can slide over each other, it is soft and slippery. Therefore, it is used as a lubricant for engines and locks, for pencil lead (clay+graphite).
Conducts the electricity because of having 1 electron delocalized for each C atom. This electron carries the charge. That is why it is used as electrodes in electrolysis and for connecting brushes in generators.
Very hard( each C is held in place by 4 strong covalent bonds). HARDEST SUBSTANCE. Used in tools for drilling and cutting stone.
Very high melting point, 3550 °C.
Cannot conduct electricity because of not having free ions or electrons to carry the charge.

12. SILICA Naturally occurs as quartz, the main mineral in sand.
Each Si bonds to 4 oxygen atoms.
Each oxygen bonds to 2 Si atoms.
Hard substance with high melting point of 1710°C. Used in bricks.
Hard, can scratch things, and that is why it is used in sandpaper.
Lets light through. Therefore, it is used for making glass and lenses

14. Allotropes of Carbon
Allotropes are different forms of the same element.