The size of an atom is almost impossible to measure because the Atom contains 20 different particles. Electrons, for instance, determine the size of an Atom. When we see the animations of electrons circling the nucleus we assume the motion as being predictable but actually, the electron particles wobble about and influence the size of the Atom. Electrons also have no predefined orbit or distance between them which can also size the Atom. Atoms are the smallest part within Ordinary Matter.
If an Atom was predictable in size it would be 100 picometers in diameter.
A picometer is 1 Trillionth of a Metre or 1 Millionth Millionth of a metre
Ionized and Neutral Atoms consist of all:
How Big is an Atom, Comparison
Iron Atoms, for example, are 280 picometres. Can you visualise 280 picometres, NO? Well, let us try and illustrate how big an Iron atom is.
If you visualise a solid steel sphere with a diameter of 6cm which is 99% iron! This steel sphere has as many iron atoms as it takes to fill the earth with the steel sphere.
In size, the whole earth is to the 6cm steel sphere to what the steel sphere is to an Iron Atom!
The 6cm dia Steel Sphere is 200 million times wider than an Iron Atom and the Earth is 200 times wider than the 6cm dia steel Sphere.