Its all about energy. Water condenses when it doesn't have enough energy to keep zipping around in the air. This means kinetic energy, physical movement. Water

Its all about energy. Water condenses when it doesn't have enough energy to keep zipping around in the air. This means kinetic energy, physical movement. Water has one oxygen and two hydrogens, this makes for a pretty polar molecule. At a purely mechanistic level, you can think of polar molecules like how magnets work. N is attracted to S and vice versa. In polar molecules, + is attracted to -. When water loses energy (like through cooling down which is just when it runs into other molecules and loses energy) it doesn't have enough momentum to not stick to other water molecules. When this happens they start clumping together and can fall out of the (gas) solution. Water in air is moving around pretty fast and this overcomes the attractive force of the polar interactions with water molecules, so no clumping (water droplets) Since amount of energy (temperature) determines how much water the solution (air) can hold, dew point is the temp at which the air is fully saturated with water molecules and can't hold any more. Water will condense if the temp is lowered past the dew point if we assume a constant water content and air pressure