system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why are mercury containing amalgam tooth fillings considered safe despite mercury being extremely toxic?
gpt
The properties of elements change wildly when those elements form chemical bonds with other elements. It's why hydrogen (a flammable gas) and oxygen (a flammable gas) are not flammable when they are bonded in water, and why sodium (a violently reactive metal) and chlorine (a poisonous gas) are not deadly to consume as table salt.