I was watching some videos about elements with the kids. One of them was about chlorine gas, which is poisonous.
I mentioned to the kids that Chlorine is poisonous and Sodium is an explosive metal, so both of them would be deadly if you tried to eat them. However if you combine the two, it turns into something that you eat every day: table salt.
Then we all ate some salt.
The idea that two very dangerous chemicals could combine into something safe seems strange. So I explained it to the kids this way:
Sodium atoms have an extra electron in their outer shell, which is is why they react so strongly. Chlorine is missing an electron and that is why it reacts strongly.
So imagine that I had a bunch of toys and it was hard to carry them all. I had one toy that I did not want. I wanted to get rid of it so badly that I might throw it at you. Elijah was wanting a toy. He wanted a toy so badly that he might take a toy from you or even hit you to get your toy. We would both be dangerous. But if we bumped into each other, I would gladly give him my toy and he would happily take it. Then we would be friends and we would not be dangerous anymore.
Not the most scientific explanation that I have ever heard, but I thought it was one that the kids could grasp.
The video was: