There are a few of us ex-weather mod pilots here that I know of.
No, its not so much about weight of iodine particles, besides they are extremely small and minute. Its like an artificial ice crystal, that begins to start the glaciation process of the supercooled liquid crystals, which in itself can cause updrafts to happen from the heat released, when the water changes state from liquid to solid. For rainfall augmentation purposes, its just to try and make the natural process a bit more efficient and try to get a little more precipitation.
When it comes to hail suppression, its a similar process, but done to a heavier degree, to try to add too many condensation nuclei, so that hailstones do not have as much of a chance to grow, since there are more nuclei now for a given amount of water.
What the chemtrail loons are talking about is seeing contrails across the sky that are parallel or that cross...Thats obvious signs of a government spraying program to them. They have not caught on to aircraft navigation yet, nor do they want to.
Oh and if the trails are a bit too big and wispy or last a bit too long, they think the same.
They just have not grasped the concept of a dynamic and moveing atmosphere, with differences in temp and winds.
To them, by god if its hot on the ground, its hot up there, and if the wind is light and westerly on the ground, its that way up there. And if a trail lasts more than a few seconds, its chemicals!