C3: Structure and Bonding Flashcards
(47 cards)
What are the properties of solids?
They are hard to compress
- packed in a regular pattern with almost no space between particles
Fixed shape - cannot flow
Vibrate in place
What are the properties of liquids?
Hard to compress
-particles are close together with little space
Take the shape of the container, can flow
Slide along each other
Particles vibrate faster
What are properties of gas particles?
Easy to compress
- particles are far apart
Spread out to fill the space of the container
Move quickly and randomly
Why is it harder to change the state of some materials?
Some have stronger intermolecular forces of attraction, thus more energy is required to break them, thus the higher the melting point
What are the limitations of the simple particle model?
The model assumes all particles are solid spheres (particles have different shapes and are not solids)
Forces between particles are not shown (incorrect)
What is ionic bonding?
The bonding taking place between a metal and a non-metal. It takes place for both to achieve a full outer shell
What is a dot and cross diagram?
A diagram representing ionic bonding - only needs to show outer energy levels. Usually, metals are modelled with crosses as their electrons and non-metals are modelled with dots to distinguish the electrons.
To model ions add square brackets around the ions and the sign on the outside
What are the properties of ionic compounds?
They form giant ionic lattices (every + ion is surrounded by a - ion)
Cannot conduct electricity when solid, but can when liquid
What are the properties of giant ionic lattices?
Very strong electrostatic forces (ionic bonds) of attraction - high m.p. and b.p., lots of heat to break
Why can’t ionic structures conduct electricity when solid?
Their ions are locked in place by the electrostatic forces of attraction. They conduct when liquid because then, the ions can move and carry a charge
What is covalent bonding?
Takes place between two non-metals. They share pairs of electrons to form full outer shells
How is covalent bonding modelled as energy level diagram?
The atoms are modelled as circles with their electrons modelled as dots and crosses respectively (only outer shells required). Their bond is shown as an overlap, with their shared electrons inside the overlapping space
Why do small covalent molecules have low m.p. and b.p.?
Although the atoms are held together by strong covalent bonds, the intermolecular forces between the molecules are very weak, thus require low energy to break
What happens to m.p .and b.p. of covalent structures as their size increases?
They increase, this is because there are now more intermolecular forces, which need more energy to break.
Why don’t small covalent molecules conduct electricity?
Covalently bonded molecules have no charge, thus cannot carry a current
What is the structure of giant covalent molecules?
Many covalently bonded molecules joined together in a giant covalent lattice
What are the properties of giant covalent molecules?
Always solids at room temp.
Why are giant covalent molecules solids at room temp.?
They have millions of strong covalent bonds, taking more energy to break them
What is the structure of diamond?
Each carbon atom forms 4 covalent bonds with other carbon atoms - a single diamond contains a huge amount of these covalent bonds, resulting in a very high melting point
Why can’t diamond conduct electricity?
It contains no free electrons to carry electrical charge
What is the structure of silicon dioxide (silica or sand)?
Oxygen atom covalently bonded to a silicon atom - it has a huge number of these
What are the properties of silicon dioxide?
High melting and boiling points
What are the properties of graphite?
High m.p. and b.p.
Soft and slippery
Excellent conductor of electricity and heat
What is the structure of graphite?
Carbon atoms with 3 covalent bonds each. They form many hexagonal rings (as there’s a lot of them, graphite has a high m.p. and b.p.). These are arranged in layers which are not covalently bonded, thus they can slide, making graphite slippery. Instead, they are held together by the single electron of each carbon atom which is not in a covalent bond
