Covalent substances: Two kinds Flashcards
What are the two kinds of covalent substances?
- Simple molecular substances.
- Giant covalent structures (macromolecules).
In simple molecular substances what do the atoms form?
Very strong covalent bonds to form small molecules of several atoms.
In simple molecular substances what are the forces of attraction like between the bonds?
Very weak forces of attraction (intermolecular forces).
What happens as a result of the very weak forces of attraction in simple molecular substances?
Very low melting and boiling points.
Why are the melting and boiling points very low in simple molecular substances?
Because the molecules are easily parted from each other.
When simple molecular substances melt or boil what happens?
The weak intermolecular forces get broken (not the strong covalent bonds).
What are most simple molecular substances at room temperature?
Gases or liquids (although they can be solids).
What do simple molecular substances not do?
Conduct electricity.
Why don’t the simple molecular substances conduct electricity?
Because there no ions so there is no electrical charge.
What are giant covalent substances?
Macromolecules.
What are giant covalent structures similar to?
Giant ionic structures (lattices) except that there are no charged ions.
In macromolecules, what do the atoms form?
Strong covalent bonds (they are all bonded to each other).
In macromolecules what does their strong covalent bonds mean?
That they have very high melting and boiling points.
What don’t macromolecules do?
Conduct electricity (not even when molten).
What macromolecule is an exception to the rule that they don’t conduct electricity?
Graphite.
What are the main examples of macromolecules?
- Diamond.
- Graphite.
- Silicon dioxide (silica).
What are the bonds like in diamond?
Each carbon atom forms four covalent bonds.
What structure does diamond form its covalent bonds in?
A very rigid giant covalent structure.
What does diamonds structure make it?
The hardest natural substance.
What is diamond used for?
Drill tips.
What does diamond look like?
Sparkly.
What is silica?
What sand is made of.
In silica what is each grain of sand?
One giant covalent structure of silicon and oxygen.
What are the bonds like in graphite?
Each carbon atom only forms three covalent bonds.
