Teaching children about metalloids is much more fun if you can incorporate a practical activity. This simple experiment is engaging and fun.
Conducting this activity will provide the perfect opportunity to discuss the properties of metalloids and in particular boron.
Metalloids are also known as semi-conductors and have both metallic and non-metallic properties. The metalloids are: Boron, Silicon, Polonium, Germanium, Arsenic, Antimony & Tellurium. In this experiment we use Borax which is a Boron compound as it also contains sodium and oxygen.
I would advise that all experiments are conducted in a clean, safe environment and that children are wearing protective eye wear. The putty can stain materials so I would advise wearing aprons as well. Borax should not be ingested so if your children are very young be extremely vigilant. If you have sensitive skin then protective gloves are a good idea when handling the putty. I always remove chemicals or similar from the table as soon as they have been used and store them well out of the reach of children.
What you will need.
- Borax 2 tbsp ( this can be bought online).
- PVA glue 1/4 cup.
- Water 3/8 cup ( roughly half a cup plus 2 tbsp).
- Food colouring a few drops ( green looks the most slime like but any bright colour will do).
- Clear jar ( I use a Pyrex jar as Boron is used to make borosilicate glass better known as Pyrex).
- Add the Borax to 1/2 cup of water and stir. If it doesn’t dissolve well you can heat it up in the microwave for a few seconds to speed up the reaction.
- Add the PVA to the remaining water with the food colouring and stir.
- Add a spoonful of the borax solution to the PVA and watch what happens. Add a spoonful at a time until you have ‘putty’.
- Remove the putty and play with it. Ask children to describe how it feels. Does it feel wet? Is it a solid or a liquid? Examine how it behaves. If you pull it quickly what happens? If you pull it slowly what happens?
What has happened.
PVA (polyvinyl alcohol) is made of long molecules. Borax links these long molecules together to form a net. The water molecules are trapped which is why it feels wet but doesn’t wet your hands. This is a non- Newtonian fluid which means that it will behave differently depending on the stress applied to it. If you apply high stress – pull it quickly – it will snap. If you apply low stress – pull it gently – it will stretch.
You can also explain that glass is toughened with boron to form borosilicate glass. It can withstand high temperatures which is why most people use Pyrex cookware. It may amuse children to store their putty in the Pyrex jug afterwards.
The putty can be kept in a sealed container for a week or so but it will go mouldy at some point. Make sure it is disposed of if this happens.
You can see how the PVA changes in this short video.