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Why is an atom electrically neutral?
Question Date: 2014-08-15
Answer 1:

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 important.

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 discussion here 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 exposition overall).

Hope this helps!

Answer 2:

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 ions.

Answer 3:

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 electrically neutral.

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 electrons).

Answer 4:

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.

Answer 5:

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!

Answer 6:

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 slight charges.

Answer 7:

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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