C2 - Types of Substance Flashcards
Describe covalent bonding.
Between two non-metals.
Electrons are shared in pairs.
Double, single or triple bonds.
Very strong.
Describe ionic bonding.
Between a metal and a non metal
Electrons given away and taken in.
Form ions.
Very strong because of the attraction between oppositely charged ions.
Hard to separate - high melting points, high boiling points.
Form a giant lattice structure meaning there are lots of attractions to break.
Conducts electricity in a a liquid (dissolve or melt it) because IONS ARE FREE TO MOVE.
Describe molecular covalent/simple covalent.
(THINK THIS IF IT TALKS ABOUT LOW MELTING/BOILING POINTS!)
For small molecules (eg. O2, CO, CO2, H2, H20, F2, B2, CL2)
Very strong covalent bonds in the molecules.
No bonds between the molecules - only weak intermolecular forces of attraction.
Very easy to overcome these forces, easy to separate so very low melting and boiling points.
Describe the bonding in diamond.
Made up of many carbon atoms.
Each carbon atom is bonded to four others with very strong covalent bonds.
In a giant structure - thousands of covalent bonds.
This makes it very strong, giving it extremely high melting and boiling points and making it very hard because you have to break all the strong covalent bonds.
Describe the bonding in graphite.
Made up of many carbon atoms - each carbon atom is bonded to 3 others.
The atoms sit in layers in a 2D structure.
The spare electron becomes delocalised and sits between the layers allowing them to slide over each other.
It can conduct electricity because the electron is free to move.
Describe metallic bonding.
Metals have either 1, 2 or 3 electrons in their outer shells. They give these electrons away to form ions.
They sit in layers which makes them easy to shape.
The sea of delocalised electrons allow electricity to be conducted.
What is the difference between thermosoftening and thermosetting plastics?
Thermosetting
Made up of long polymer chains
Bonds form between the chains
Cannot overcome the bonds so cannot reshape.
Thermosoftening
Made up of long polymer chains
No bonds between the chains - only weak intermolecular forces
Easy to overcome weak intermolecular forces with heat
Easy to soften and reshape.
Describe fullerenes.
They are made of carbon - upto 60 carbon atoms.
Made up of hexagonal rings.
Easy to shape and make balls and tubes with. You can put other chemicals inside.
They are strong but very light (good use - tennis rackets).
What are alloys?
A metal mixture. NOT compound.
Why are alloys stronger than normal metals?
Because the atoms are different sizes.
This distorts the arrangement of atoms being in neat rows.
It prevents the layers from sliding over each other.
This makes it stronger.
What is a shaped memory alloy?
An alloy which returns to it’s original shape upon heating.
