Why Colloidal Metals Cannot Be Single Atoms

I often read erroneous statements on colloidal silver and gold websites that state that their particles are the size of a single atom. This is physically impossible unless their product contains only one atom, or if its not really a colloid at all, but is ionic like gold chloride.

I will attempt to explain by example why this is not possible, and the metals will always aggregate to a certain size.

Because its so hard to visualize atoms, lets talk about basketballs.

Suppose we had a room with lots of basketballs all colored orange and covered with sticky glue. These represent our metal atoms. These basketballs are moving about (brownian motion) and collide with each other. What would happen? The balls would stick to each other making a large particle.

Even in the macro world of huge things, this happens. It is known as cold welding and hammer welding. Transistor cases (the old round metal kind) were welded together just by squeezing in a press. Blacksmiths routinely welded iron simply by heating it up to make the atoms mobile, and smashing with a hammer to bring them close enough.

Back to the basketballs.

Suppose we don’t want the balls to glue themselves together. We could add something else to the room to keep them apart. Lets add some cylinders about the same diameter as the ball, but two or three times as long and sticky on one end. (This represents a stabilizer molecule) What would happen? The sticky end of a cylinder would meet up with a basketball, and they would stick together. Soon you would have a mix of naked basketballs and basketballs with cylinders attached.

But what happens when the other end of a basketball/cylinder meets another basketball or a basketball with a cylinder attached? If they crash into each other at point where the cylinder is not attached to the basketball, they will touch ball to ball and weld together. Now the particle size is two atoms. It has grown, even though there is cylinders of stabilizing agents in the room.

Take a mental look at the metal atoms, now joined into two, and see the cylinders attached to them. There is plenty of surface on the atom group that is not covered by the cylinders. Bare sections of the basketball group will continue to collide with other basketball/cylinders until there is no more surface on the group of basketballs that do not have cylinders attached…. no more bare basketballs in the group.

As you can imagine, the physical size of the stabilizing material will make a difference in how big the cluster of basketballs can grow. If the stabilizer is very large like 10 times the diameter of a ball, not many chunks of stabilizer can fit around a cluster of basketballs, but basketballs could sneak through the space between the stabilizers. If the stabilizers are not sticky enough, they will not survive collisions between the balls, and will allow the basketballs to touch and weld.

Can you see it?

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