Bjerrum length

Imagine you are building a wall with Lego bricks. Each brick has little nubs on the top and bottom that help it stick to other bricks when you stack them together. But sometimes you might notice that some bricks just won't stick together no matter how hard you push! This happens because the nubs on each brick have a certain distance they can reach out and attract other nubs. If the two bricks are too far apart, they can't stick together.

This same idea applies to molecules in water. Some molecules have a positive charge on one side and a negative charge on the other side, just like nubs on a Lego brick. These charges can attract opposite charges on other molecules, pulling them together to form a bond.

But there's a catch. Water molecules are very good at blocking these charges from pulling too close together. The positive and negative charges on opposite molecules will feel an attraction to each other, but as they get closer and closer, the surrounding water molecules start to resist their approach. This is kind of like trying to join two magnets that are being pushed apart by a third magnet in the middle.

The Bjerrum length is the distance at which the charges on two different molecules in water start to feel this resistance from the water molecules around them. It's like the maximum reach of the nubs on a Lego brick. If two molecules are closer than the Bjerrum length, they will join together and form a bond. But if they are farther apart, the resistance from the water molecules will keep them apart, just like two Lego bricks that won't connect because they have reached their maximum reach.