I started with the Montessori presentation (but tweaked it slightly to include Plasma)
Don't panic - I know grapes aren't plasma but it will all make sense shortly (and it got the kids really curious)
We discussed each state in depth;
Solid - Particles close together in a fixed position. Has a definite volume and shape. Looked at different types of solids.
Liquid - Has a definite volume but no definite shape. Particles are close together but free to move.
Gas - Doesn't have a definite shape or volume. Particles are far apart and have complete freedom to move.
Looked at how gas fills up the whole container.
Plasma - Very similar to gas but made up of groups of positively and negatively charged particles. Discussed how it is abundant in nature (stars, sun, lightning, northern lights etc).
Then the grapes came into play using Supercharged Science's grape plasma experiment. to create our own plasma.
Next we discussed the arrangement of particles and used pom pom's to get the kids to demonstrate.
Then moved onto compressability - using a syringe we placed a pebble in and they tried to squish it, then filled it part way with water, covered the end and tried to squish it and finally filled it part way with gas, covered the end and when squished it halved in volume.
We discussed the attractive force between molecules in each state and got the girls to make posters.