|Why is an atom electrically neutral?|
|Question Date: 2014-08-15|
By definition, an atom is electrically neutral
(i.e. has the same number of protons as it does
electrons, plus some number of neutrons depending
on the isotope). If a species were charged, it is
referred to as an ion (cation for positively
charged and anion for negatively charged species),
also by definition.
But this is probably not a very satisfying
answer. (I personally find answers based on
definitions pretty bland.) Perhaps an interesting
follow up question is...
Is the universe electrically neutral?
For many instances in science, we deal with
systems where charge neutrality is very
Perhaps a common example you might be familiar
with is table salt, NaCl. Before forming
salt, both sodium (Na) and chlorine (Cl) are
electrically neutral atoms. Then chlorine nabs an
electron from a sodium because it is more
energetically favorable for it to have an
additional electron. You then have a Na+ cation
and Cl- anion that combine into NaCl due to
electrostatic attraction. Overall, NaCl is a
neutral system (table salt doesn't shock you when
you eat it... hopefully).
This property of electrical neutrality is also
very important in the work that I do every day. I
do computational research on crystals like NaCl
where we calculate energies of a variety of sorts
to understand the material. Part of calculating
the total energy of a system for a crystal like
NaCl involves the energy contribution that arises
from Coulombic forces between every combination of
Na+ and Cl- anion. This would mean figuring this
out for something like 1023 ions (which
is a lot). We do something a little more clever.
NaCl is a crystal, which means it has a periodic
(i.e. repeating) structure, so we only need to
consider a unit cell, or small portion that can
reproduce the entire crystal structure by
translating it. But this means what we model is
infinitely large materials. This is okay for bulk
materials, since surface effects are small.
What is more worrying are those long range
Coulombic forces. If we're not careful, we could
end up with infinite energy! And that would be no
good. This can be solved with a clever way of
adding Coulombic forces (called Ewald
summation) and a charge neutral unit cell.
But if many everyday things we are familiar
with are electrically neutral, does this mean that
the universe has to be electrically neutral?
It's actually still an open research question.
What do you think would happen if the universe
were just slightly positively charged overall?
This is different from being ionized- that just
means there are positively and negatively charged
particles. But do these particles have to just
balance each out? You can follow an interesting
or a pretty recent article
about how the universe could be slightly
positively charged (the math gets a little hairy
towards the end, but there luckily is more
Hope this helps!
Atoms are made of 3 sub-atomic (smaller than an
atom) particles: neutron (neutral), protons
(positive), and electrons (negative). When an atom
has the same number of protons as electrons, the
charges balance each other and the atom is
neutral. If the atoms aren't neutral, they are
very reactive and will react with nearby atoms to
form compounds or perform other reactions. Because
the air around us contains many gas molecules, any
charged atoms (called ions) will quickly react. If
you want to keep free ions you need to have a
really good vacuum with no other atoms around that
can react with the free ions. The opposite of free
ions are bound ions, which are quite common. These
are ions that have reacted with other atoms to
make a stable compound, like table salt, which is
made of positive sodium ions and negative chloride
When an atom is electrically neutral, it means
that the overall charge of the atom is zero. Atoms
are made up of positively charged particles called
protons and negatively charged particles called
electrons as well as non-charged particles called
neutrons. The charge from a proton or electron are
of equal strength, therefore if an atom has an
equal number of protons and electrons, it will be
However, atoms are not always electrically
neutral, in which case they are called ions. An
ion is an atom that has lost or gained electrons
resulting in a positive charge (from losing
electrons) or a negative charge (from gaining
They don't have to be. In an atom, there are a
certain number of positively-charged protons.
Positively-charged protons attract
negatively-charged electrons, but the
negatively-charged electrons repel one-another. As
a result, the atom can attract a number of
electrons until it has equal numbers of protons
and electrons, making the atom neutral.
There are a lot of ways to make a non-neutral
atom, though. For example, table salt, in water,
breaks up into negatively-charged chloride ions
(chlorines with one extra electron), and
positively-charged sodium ions (sodium with one
too few electrons). Why this happens has to do
with quantum mechanics, which is a college-level
chemistry topic. Also, high-energy light or other
forms of energy can strip the electrons from
atoms; this is why ultraviolet light causes
sunburn, for instance, because it strips the
electrons from the atoms in your skin.
Well, let's think about what makes up an atom:
an atoms consists of a bunch of negatively-charged
electrons orbiting around a nucleus, which is made
up of neutral neutrons and positively-charged
protons. In pretty much all atoms, the number of
electrons and protons is the same, so the net
charge of the atom in zero.
But what if the atom has more or less electrons
than protons? Well, then the atom becomes
electrically charged - this is called an ion
(which are super important, by the way! Ions are
super important to a ton of stuff, including
making sure your body works correctly!). If the
atom has more electrons than protons, it is
negatively charged, while if it has fewer
electrons than protons, it becomes positively
charged. However, remember that opposite charges
attract and like charges repel: so, a
positively charged atom will attract electrons
until it becomes neutral, whereas a negatively
charged atom will repel some of its electrons
until it also becomes neutral. So only neutral
atoms are stable.
Hope these help!
Atoms are neutral if they have the same number
of charged protons and electrons, balancing
positive and negative charges. As long as the
numbers of electron and protons are the same, the
charges will balance. Sometimes atoms are more
stable though when they are not perfectly
electrically neutral. These charged atoms are
called "ions." If you put salt in water, its
molecules actually break apart into individually
charged atoms. This is because water itself has
Atoms are electrically neutral because they
have equal numbers of protons (positively charged)
and electrons (negatively charged). If an atom
gains or loses one or more electrons, it becomes
an ion. If it gains one or more electrons, it now
carries a net negative charge, and is thus
"anionic." If, on the other hand, it loses one or
more electrons, it now carries a net positive
charge and is "cationic."
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