We are currently studying atoms and the periodic
table. A student asked a question today that I
thought was quite perplexing. Since an atom is
mostly empty space between its nucleus and
electrons, what exactly is that "empty space?"
From my amateur point of view it can't be a
vacuum, can it? And, there can't be matter of any
sort because we're on such a small scale (and
atoms make up matter). Thanks for the help. Love
the site. Confused by the empty, PJ Creek 8th
grade science teacher.
|Question Date: 2017-11-29|
Excellent question, which is actually a bit of a
complicated question to think about.
Quantum mechanically (I know, I know) you
consider a few things:
These sub-atomic particles
like electrons, protons and neutrons are quantum
objects. They have what is known as a
which can be considered a likely area, or
probability, of the particle's location.
are quite spread out around the nucleus, which is
why this area is referred to as an electron
"cloud". So, electrons are smeared over
this "empty" space. Additionally, the
the nucleus and the electrons of an atom are
constantly interacting, either electromagnetically
or through what is known as the weak force. These
particles are exchanging photons (in the case of
electromagnetism) or heavy gauge bosons (in the
case of the weak force ). So you can say
'empty' space between the electrons and nucleus is
'filled' by these forces.
I think it is fine to call what is in between
everything empty space in the atom if you took a
snapshot of the atom, but also consider that there
are also energy fields and the probability of an
electron occupying that space all at once in
Hope that helps!
In fact, there is no "empty space" in an atom.
To understand this, we need the full
quantum mechanics understanding of
electrons. In quantum mechanics, an electron is
not a point particle, it is a distribution of
"probability cloud" (wave function of the
electron), usually called the "electron
So in an atom, the nucleus is surrounded by
electron cloud in the full space inside an atom,
so there is actually no empty space between
nucleus and electrons.
According to quantum mechanics, nucleus
itself is also a "cloud", but because nucleus
is much heavier than electron, the size of its
cloud is very small, so usually we can still view
nucleus as a point.
In the classical picture, the electrons will orbit
around the nucleus in the fixed orbitals , pretty
much like the planets orbiting around our sun with
lots of empty space in between. But there is one
big development in the 20th century, which is the
idea of quantum effect. When things are
small, quantum effects are not negligible anymore
and will play big roles.
In the modern picture, the electrons will still
orbiting around the nucleus, but with no fixed
orbitals (here I mean those classical orbitals).
Instead, those electrons are constantly moving,
with probabilities to show up around the nucleus.
We still use the orbitals to describe the motions,
but the meanings are different. Here is a website
that you can get a glimpse of those orbitals (s,
p, d, f orbitals, etc..): orbitals
I will give one example. In the simplest case,
like H atom (hydrogen). The sole electron
will take the s
orbitals, which is isotropic . It means
sole electron will show up in any direction with
equal probability. There is one more thing, which
usually is not easily to show, the probability for
the electron to show up is distance dependent
(here distance means how far away the electron is
to the nucleus, denoted as r ). It is a peak
function, which means that the electron
up with a maximum probability at distance
important thing to know is the electron can also
show up very close or very far away from the
nucleus, though with smaller probabilities.
classical picture, the electron will pretty much
stay at the same distance r0 to the
in the modern picture, it is more or less true. It
has the biggest probability to stay at such
distance, but it can also be closer or further
away with smaller probabilities.
So those space is not the vacuum that we are
usually talking about.
What is actually happening is that each particle
inside of an atom has a cloud of probability as to
its actual location , with the electrons having
large (r) clouds while the protons and neutrons
have tiny clouds in the very center. These clouds
of probability take up the entire size of the
atom, and they overlap - for example, the
probability clouds of the two electrons in a
helium atom perfectly overlap one-another.
electron "orbitals" (cloud sizes and shapes) come
in pairs, which is why the length of every period
in the table is a multiple of two (H to He is 2,
Li to Ne is 8, Na to Ar is 8, K to Kr is 18, and
so on). So, technically, the space in an atom is
not vacuum, because it is filled with these
In order to fully understand what is going on, you
need a little understanding of Mquantum
which explains why different elements fall where
they do on the periodic chart. Working this out is
the discovery for which Richard Feynman won the
Nobel Prize (the theory of quantum
as it is called). A good, college freshman-level
chemistry textbook should explain it in detail
well enough for you, an adult, to grasp it.
Explaining it to eighth graders then becomes
trickier as it involves mathematics that is just
at or slightly beyond their level. For example,
the length of any period is given by the following
L = 2 x (((n + 1) / 2)2)
where n is the number
of periods down in the table (round fractions up
to the nearest integer). So, 2, 8, 8, 18, 18, 32,
32, 50 - and that's all of the elements that we've
discovered that are stable because of nuclear
physics, but if there were more stable elements,
in a neutron star perhaps, then the sequence would
This is a great question! You’re right it
saying that the space between the electrons and
the nucleus is empty space but it’s important to
keep in mind the way that electrons move.
They don’t orbit the nucleus at a set distance
rather they exist at multiple locations in a sort
of cloud around the nucleus. The electrons
are moving so quickly through such a small space
that it almost seems like they are in multiple
spaces at the same time! In fact the quantum field
fluctuations that the electrons cause almost fill
up this entire space around the atom. This video
may be a little advanced for your class but the
visual demonstrates the idea very well:
Thank you for your question!
The simple version of the story is yes, it
is empty space even though it is weird to think
Nearly all the matter that makes up an atom is
in the nucleus, but the size of the atom is
determined by the radius of the outer electron
shell, so most of the atom is indeed empty
(i.e. is not made up of matter). The reason
that I cannot (unfortunately) walk through walls
is because the electrons that make up the outer
shell of my atoms repel the outer electrons in the
atoms that make up the wall. However, there are
particles that do not interact with the
electromagnetic field, and these can pass through
atoms. For example, neutrinos are
small particles, which do not feel the
electromagnetic force and thus can fly right
through walls (or the earth itself), because the
wall is mostly empty space.
A more quantum mechanical perspective
would say that the simple picture of a point
electron sitting in a defined location around the
nucleus is not really correct. It is more
realistic to conceptualize the size of the atom
as being defined by an electron cloud of
probability. There is a finite probability to
find an electron anywhere inside the cloud region
and so the space around the nucleus is really
occupied by some electron probability
density or field. Think about a magnetic
fieldas an analogy. The magnetic field
occupies a volume, but it appears that there is
nothing there (empty space), and I would not know
it was there unless I put a magnet into the field
and observe that the magnet is pushed by the
Try pushing two north sides of a magnet
together and you will see they repel each other.
On the atomistic scale this is very similar to
what is going on when I put my hand against the
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