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Name: Henrik
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Hi, I keep hearing that we are all made out of atoms, atoms that are made out of basically nothing but a few electrons and a nucleus. Hence we are all made out of mostly "nothing". My question is how much of an atom is vacuum? On an average compared to the size of the nucleus how far away is the electron "orbiting?" Say the core would be the size of a tennis ball, how far away would the electron be swerving?

Responding to this question requires addressing a common misconception first. Subatomic particles are not exactly like "really small balls" -- thus, it's not quite right to envision the atom as 'little balls' (electrons) orbiting a 'slightly bigger ball' (the nucleus). A whole branch of physics known as 'quantum physics' deals with all the weird properties that very small particles exhibit. Most notably, these particles are not like little hard spheres -- they can act like waves too, or even like 'smears' of particles across a given area. So, it is a bit misleading to think of 'space' between electrons and the nucleus. There are areas that electrons are more or less likely to be found, but not a tight distinction between 'space' and 'particle'. I am not sure your grade level, so I do not want to go into too much detail, but if you want more information, I suggest you read about wave-particle duality and wavefunctions to find a more thorough answer.

Hope this helps,

Burr Zimmerman


Not all atoms are the same size, so to make this answer mean something I will choose an atom of medium size - Iron Its atomic number is 26, and it has an atomic radius of approximately 150 pm (That is picometres - a million millionth of a metre - 10^-12) Its nuclear radius is something in the order of 5 fm (that is femtometres - a thousandth of a million millionth of a mietre - 10^-15) So the atomic radius is some 30,000 times the size of the nucleus. A tennis ball has a diameter of 2.5" so the matching atomic radius is approximately 1.2 miles -- in metric - ball diameter of 62.5mm gives a radius of 1.88Kms

Keep in mind though, that the electrons do not all spin at that distance, nor do they not do it all the time. Electrons are considered to spin in a diffuse cloud with some close to the nucleus and others further away. They also fluctuate, changing their distance from the nucleus and vibrating in such a way that they do not repeat their path, but trace a path like string being wound onto a ball. The atomic radius is the distance at which the electrons 'run out'. Since this is hard to define, there is some dispute as to how atomic radius should be calculated or measured, and so the answers vary a bit as well.

I hope this is useful.

Nigel Skelton

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