C2 Structures and Properties Flashcards
What are the key properties of ionic substances?
- high melting point
- conduct electricity when molten or dissolved, but not when solid
- brittle
What are the key properties of simple molecular substances?
- low melting point
- do not conduct electricity
What are the key properties of giant covalent substances?
- High melting point
- Do not conduct electricity
- Hard
Which giant covalent substance is unusual because it conducts electricity?
Graphite
What are the key properties of metals?
- High melting point
- Conducts heat and electricity
- Malleable (can be hammered into shape)
- Ductile (can be pulled into wires)
What holds the ions together in an ionic substance, for example sodium chloride?
The ions are oppositely charged (sodium is positive and chloride negative) and so they are attracted to each other by a strong electrostatic force.
What holds the atoms together in a giant covalent substance?
Covalent bonds
Why do ionic substances have high melting points?
The electrostatic force holding the ions together is very strong, so a lot of energy is needed to separate the ions,
Why do ionic substances conduct electricity if the substance is molten or in solution?
The ions are free to move and carry the current.
Why can’t solid ionic substances conduct electricity?
The ions are fixed in position so cannot move.
Why can metals conduct electricity?
The delocalised electrons are free to move and carry the current.
Why are metals malleable and ductile?
The layers of atoms are able to slide over each other.
Why do giant covalent substances have high melting points?
There are lots of strong covalent bonds that take a large amount of energy to break.
Why can’t covalent substances conduct electricity?
There are no delocalised electrons
Why do molecular substances have low boiling points?
There are weak intermolecular forces between the molecules which do not take a large amount of energy to overcome.
The covalent bonds within the molecules are not broken.
Describe the bonding and structure in graphite.
Each carbon atom is joined to 3 others by covalent bonds. One electron from each carbon is delocalised.
The atoms form layers which can slide over each other.
Why are alloys harder than pure metals?
The different-sized atoms distort the layers which means the atoms can no longer slide over each other easily.
How does the structure of thermosoftening plastics explain their properties?
They are made up of lots of long chains with weak intermolecular forces between the chains. These are easily broken allowing the chains to slide past each other.
How does the structure of thermosetting plastics explain their properties?
The chains are fixed into a rigid structure by cross-links between the chains that are covalent bonds and therefore very hard to break, even at a high temperature.
