Notes to teachersThis slide should NOT be

displayedThe purpose of this presentation is to…

•Introduce the basic science behind the “Goo” experiment / investigation.

•There is an opportunity to emphasise that there are a number of representations used to explain what happens in nature. These are NOT actually what happens, but that they are “Models” to help us visualise a specific set of circumstances.

•The presentation is NOT intended to teach topics for the first time, but to revise some aspects of chemistry (monomer / polymer / covalent bonding) and to give an insight into an aspect of chemistry at A’ level (polarity, H bonding).

•Taken with the experiment, there is an opportunity here to highlight the fact that chemistry and physics can be linked together to modify the mechanical properties of a polymer by using a reaction to cross link polymer chains and design a polymer with a specific viscosity. An investigation of viscosity v cross links could follow. This using science for practical (and commercial) use is Materials Science.

Goo – How it works

(Without getting too stuck on details)

Martin Carr(Oxford University Department of

Materials)

email: Martin.Carr@materials.ox.ac.ukweb: http://outreach.materials.ox.ac.uk

Easy Words

Goo is made from a polymer called…

Poly Vinyl Alcohol

…which is the main part of PVA glue

Poly = Lots of identical bits

Vinyl = Name for repeat units of C-C

Alcohol = A special, covalent –OH group

Easy Molecules

This is how we represent Vinyl alcohol…

C C O

C C

O

C C OH

C COH

C2H5OH

C2H3OH

This is how we represent ordinary alcohol…

Easy Polymer

C C

OH

n

Hundreds of thousands of Vinyl Alcohol monomer molecules (mer means molecule) join together in a chemical reaction to make a Polymer.

The molecule is too big to draw every single atom, so we have a shorthand where “n” is the number of joined monomer molecules…

Medium – Bonding

O H

• The electrons are NOT always equally shared

• Polymers are made using covalent bonds to join atoms.

• Electrons are shared between atoms.• The Alcohol, -OH, also uses covalent bonds.

Slightly-ve

Slightly+ve

Slightly-ve O H

Representing a Polar molecule

Harder – Hydrogen Bonding

C C

OH

C C

OH

C C

OH

C C

OH

C C

OH

C C

OH

…are next to similar molecules…The groups attract and make it harder to

slide past each other.

Long Molecules with lots of Polar, -OH, Groups

Electrostatic Attraction(Hydrogen Bond)

The Finale

Borax -- ion

C C

OH

C C

OH

C C

OH

CC

OHC

C

OH

CC

OH

CC

O

H

CC

O

H

CC

O

H

The Borax 2- anionAttracts more stronglyAnd holds moreChains together

Thank You For

Listening.

Now it’s your turn…