Carbon Allotropes and Molecular models

Introduction
Public summary: 

Explore some elements and different types of bond and explore ways carbon can bond to form different allotropes.

Useful information
Kit List: 

Periodic Table of Elements
Molymod kits - general, graphite, diamond
Sample of graphite (pencil lead), maybe some others

Packing Away: 

Lives in a small blue box 'Periodic Table, Alloys and Carbon Allotropes'

Frequency of use: 
1
Explanation
Explanation: 

Start of by discussing the Periodic Table, and how the valency of a compound can be determined from this. You'll need to talk about the groups going down the table and how the group number corresponds to the number of outer shell electrons of the elements in that group. You might want to talk a little bit about the behaviour of the elements in each group - like how group 1 alkali metals are really reactive in water (some kids might have seen Li or K in water at school), or perhaps how group 0 (Noble gases) are happy as they are and are unreactive. Introduce the idea of full outer shells - this should make covalent bonding a bit easier to understand.

Introduce covalent, ionic and metallic bonding, using the diagrams provided in the kit.
- Covalent bond = shared pair of electrons. Normally get this between non-metals, things with a small difference in electronegativity (this could be a little complicated to explain, but try to talk about the nucleus pulling the electrons towards it; more positive nucleus will be better at pulling electrons towards it than a big, diffuse one, kind of like a tug-of-war). Examples include CO2, O2, CH4... Also giant covalent structures, like diamond or SiO2 - very high melting points because covalent bonds are strong.
- Ionic = one atom pulls an electron off the other to form ions, then positive and negative ions (anions and cations) attract one another. Usually metal with a non-metal. Could talk about salt (NaCl) which has this sort of bonding.
- Metallic = the strong electrostatic attraction between the sea of delocalised electrons and positive ions in a lattice. Metal atoms donate electrons to this "sea", which is between the ions and you can say it holds the metal together. Emphasise the regularity of the structure - it's a lattice, with layers that can slide over each other when you shear them. Examples of metals should be things kids know, but they might get confused with some alloys - i.e. steel = iron and carbon, whilst iron is a pure metal.

Also refer to the samples of each provided. For example, metal is ductile as layer of ions can be made to slide over each other and the sea of delocalised electrons can move along with it. Whereas covalent bonding is directional so if a bond breaks, it just snaps. Metals conduct electricity - why does this happen? Encourage kids to think about what electricity is - the flow of charge (i.e. electrons or ions), so the sea of delocalised electrons in a metal means it can conduct. Also consider the idea of ionic materials - is salt conductive? Answer = no, but it can be in solution or when molten. Get kids to think about the fact that electricity has to flow, implying motion, but the electrons in ionic compounds are all too strongly held by the ions to move. But, in a liquid state, the ions themselves move (which they can't in the ionic lattice) and electricity can flow. Maybe extend to whether water can conduct (it can't) and the effect of having ions free to move in water on conductivity - do they think the water from the tap is going to be pure? Ionic compounds form strongly bonded salts, can explain solvation and why they dissolve in solution (water = polar molecule so the different ions can be "broken up" by water because of attraction to different parts of the molecule).

Then introduce the diamond and graphite structures. Ask them what they know about diamond, most should know it is the hardest material on earth. Ask them from looking at the structures to say which they think it is and why. Explain that it clearly isn't the graphite as the layers easily slide over each other. Then introduce graphite as pencil lead; say this is how it writes - layers of graphite slide over each other, leaving some on the paper. If people still follow, explain that there is a free electron from each C between the layers. These are delocalised so can conduct electricity. Next take a piece of graphite and show that you can put charge through it.

Allotropes of carbon include graphite, diamond, lonsdaleite (hexagonal diamond), C60 buckminsterfullerene, C540, fullerite, C70 fullerene, amorphous carbon, and single-walled carbon nanotube. Nanocarbons have lots of potential uses...

You can show how graphite is diamagnetic by balancing some pencil lead off the edge of a table and using either the north or south pole you can repel it. If you try this with a magnet balanced one way will attract. In contrast you may find some varieties are parmagnetic. These effects are small so you'll need a strong magnet.

Risk Assessment
Date risk assesment last checked: 
Sat, 02/02/2019
Risk assesment checked by: 
Grace Exley
Date risk assesment double checked: 
Sat, 02/02/2019
Risk assesment double-checked by: 
Conor Cafolla
Risk Assessment: 

Use Molymods and Periodic Table, along with samples of materials to explain the properties of various materials.

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Small parts Choking on small parts. 3 4 12 Watch carefully over children, use pre-assembled models so fewer small parts.
In the event of a piece being swallowed, encourage child to cough. Call a first aider, who may perform the Heimlich if trained and happy to do so.
2 3 6
Graphite Electric charge through graphite (small shocks). 2 2 4 Use small charge.
Call first aider if required.
1 2 2
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