This is a fun and easy slime to make. Make it with white glue for opaque slime, or glue gel for translucent slime.
The glue has an ingredient called polyvinyl acetate, which is a liquid polymer. The borax links the polyvinyl acetate molecules to each other, creating one large, flexible polymer. This kind of slime will get stiffer and more like putty the more you play with it.
Store it in a plastic bag in the fridge, to keep it from growing mold.
This slime is similar to the one above, but creates a less rubbery and more transparent slime. This is the real gooey deal! (This slime is non-toxic, but still keep these chemicals away from unsupervised children and wash your hands after playing with the slime.)
While water is a liquid made up of individual H2O molecules, polyvinyl alcohol is formed of long chains of connected molecules, making it a liquid polymer. (The term polymer comes from the words for "many parts.") The borax acts as a "cross-linker," linking the individual PVA chains to each other so they connect to form a blob of slime. It does this linking job when the borax molecules form hydrogen bonds with molecules present in the PVA chains. (The partial positive charge of hydrogen atoms attracts the partial negative charge of oxygen atoms.) Since hydrogen bonds are weak, they can break and reform as you play with the slime or let it ooze on a flat surface.
Your slime will last for a while if you seal it in a plastic bag and keep it in the fridge.