Let's look to the periodic table for our answer! The periodic table tells us information about every element in existence in its neutral state. The neutral state of an atom is when it's net charge is zero; that is, the number of protons equals the numbers of electrons. Oxygen is the eighth element in the periodic table, with the symbol O. This means that it has eight electrons in its neutral state. Since it is neutral, it also has eight protons!

The periodic table has another number associated with every element, and that is it's atomic mass. For oxygen, the atomic mass is 16 AMU (Atomic Mass Units). In terms of mass, protons and neutrons have about the same mass, and electrons have very little mass in comparison. Protons and neutrons each count for one AMU, and the electron counts for zero AMU. So, if the atomic mass of oxygen is 16, that means we have a total of 16 protons and neutrons. 16 total protons and neutrons minus 8 protons leaves us with 8 neutrons.

This calculation can get surprisingly tricky! The atomic mass of an element is an average over all of the isotopes of each element. An isotope is an element that has a different number of neutrons in different atoms. The chemical properties of the element don't change, but the atomic mass of the element is different if it has, say, 8 neutrons versus 9 neutrons. Because the atomic mass of each element is averaged over every stable isotope of that element, sometimes we see decimal numbers for the atomic mass. For example, the atomic mass of carbon (the 6th element on the periodic table) is 12.01 AMU. This tells us that most carbon atoms have 6 protons and 6 neutrons, and some carbon atoms have 6 protons and maybe 7 or 8 neutrons.

Most carbon atoms have 6 protons and 6 neutrons, so the atomic mass is very close to 12 AMU. Scientists have found the relative abundance of each element and isotope, so we can look up how common an isotope is. For oxygen, the isotope with 8 protons and 8 neutrons makes up 99.7% of all oxygen atoms, so its a safe bet to say that oxygen almost always has 8 protons and 8 neutrons.

I'll start by answering the question directly: in general, elemental oxygen has 8 protons, 8 neutrons, and 8 electrons. Your question is an interesting one, because it is often the starting point for many other questions we can ask about elements, chemicals, and materials.

For instance, though we often refer to the gas we breathe as just "oxygen", it is actually the molecule O₂ (two oxygen atoms bonded together).

The reason for this has to do with the number of electrons oxygen has. Electrons have a certain way of arranging themselves on atoms, and we can think of electrons as existing in "shells" around the atom's nucleus. For now we can think of atoms as having "inner" and "outer" shells. Oxygen has an inner shell that can hold 2 electrons, and an outer shell that can hold 8. Shells are filled from the innermost to the outermost, so since oxygen has 8 electrons, we put 2 in the inner shell, and the remaining 6 in the outer shell. As we can see, there's still two empty spots for electrons to go in the outer shell (which can hold 8), and the oxygen would really like to fill those spots. It does this in a clever way; it looks for a partner! If two oxygens get together, they have 16 electrons total. By "sharing" 4 of them, they each get to "keep" half of the remaining electrons (16 total - 4 shared = 12 remaining, 12/2 = 6 each). On each oxygen, 2 of these 6 go in the inner shell, and the other 4 go in the outer shell. Now, the oxygens move close together, and they share the 4 remaining electrons that they didn't "keep". This means they both get to feel like they have a full outer shell (4 that they have to themselves, 4 that are shared between them). This is the O₂ gas that you and I breathe!

This is just one example of the types of things that counting electrons can predict. Often, the number of electrons in an element can tell us about the what color it might be, whether or not it's a magnet, or what types of other elements it will react with. Also, if you ever want to know how many protons and electrons another element has, it's as easy as looking at the atomic number on the periodic table (the big number in the top of the box for each element). That number tells you the number of protons an element has, and by extension tells you the number of electrons it has. Elements are charge neutral (meaning the charges add up to 0), and since protons have a positive charge, each proton is balanced out by 1 electron, which has a negative charge. The situation with neutrons (which have no charge) can be a little more complicated, but the number of neutrons is often the same as or similar to the number of protons.

This is answered pretty completely on ScienceLine here. One refinement is to consider ions, whereas the answers at the linked question considers only neutral oxygen atoms. In general, the energy of an atom will be lower, then the valence (outermost) electron shell is full. For nearly all elements, this means gaining or losing electrons to other atoms, thus producing ions.

While the neutral oxygen atom has 8 total electrons, 2 are in the innermost (s) shell while the valence shell, which can hold 8 electrons, has only 6. Thus, oxygen tends to gain 2 electrons, for a total of 10 electrons. This results in an atom with a net charge (i.e., an ion).

In an oxygen atom, there are 8 protons and 8 electrons. Most oxygen atoms also have 8 neutrons, but it is possible for an oxygen atom to have 9 or 10 neutrons. They are just rarer. The oxygen we breathe is not in atomic form. It is in its molecular form, which is two oxygen atoms joined together by bonds, and between its two atoms, this molecule has 16 protons, 16 electrons, and most commonly 16 neutrons.

An oxygen atom contains eight protons.

Oxygen has several isotopes, and they have different numbers of neutrons. The most common isotope of oxygen is oxygen-16, which has eight neutrons; however, oxygen-18 is also relatively common, and it has ten neutrons. Both of these isotopes are stable (i.e. not radioactive).

Oxygen-17 (nine neutrons) is also stable, but is rarer. Having too many neutrons, or too few, will make the oxygen isotope radioactive, but still oxygen.

Oxygen is #8 in the periodic table. That means it has 8 protons and 8 electrons. The number of neutrons varies according to the isotope: the stable isotopes have 8, 9, or 10 neutrons(Wikipedia).

Did you know that this is the International Year of the Periodic Table - IYPT? One fun thing people are doing is finding the element that is the same number as their age. Next year my age will be the same number as Tungsten.

Here's an article about the IYPT from a chemistry magazine I get: read it here.

Generally, there are 8 protons, 8 neutrons and 8 electrons in the most abundant oxygen molecule. Here's where it gets advanced and cool! When Oxygen loses or gains neutrons it becomes an isotope. Oxygen isotopes are rarely occurring and have useful applications. For example, brain imaging in hospitals uses Oxygen 15, containing 7 neutrons.

An oxygen atom usually has 8 protons, 8 neutrons, and 8 electrons. Looking at the periodic table, oxygen has atomic number 8 and atomic weight 15.999. The atomic number tells you how many protons are in the atom's nucleus. This identifies the atom.

For example, if the atomic number were 7, then the atom would be nitrogen, with 7 protons in its nucleus. The atomic nucleus contains both protons and neutrons, but the interesting thing is that there aren't always an equal number of neutrons and protons. This information is revealed in the atomic weight, which is a number that refers to the average mass of the nucleus (in atomic mass units or amu). If all of the oxygen atoms we know about, always had 8 protons and 8 neutrons, then the atomic weight would be 16. But we know that some forms of oxygen have fewer than 8 neutrons in their nucleus, and that is why the atomic weight is a little bit less than 16. Oxygen's 8 electrons are negatively charged, and they orbit the atomic nucleus and balance the positive charge of the 8 protons. The positive charge of 1 proton exactly cancels the negative charge of 1 electron.

Oxygen is atomic number 8 on the periodic table, which means it has 8 protons! This means that a neutral oxygen atom will have 8 electrons (but this number can change! For example, during chemical reactions molecules can lose and gain electrons). The number of neutrons depends on the isotope, but a stable isotope will generally have either 8, 9, or 10 neutrons.

Thanks for your question, and let’s start with the basics: how chemical elements are defined, especially on the periodic table of elements.

The major, whole numbers above the elements on the periodic table of elements (you’ve probably seen one in your science instructor’s room) determine the element and it refers to the number of protons as a definitional part of the element’s identity. That’s the long version of this simple fact: oxygen will always have 8 protons, whether on Mars, Pluto, Earth, yesterday, or the day after tomorrow. Next, let’s consider the number of neutrons and electrons in oxygen: in short, they’re changeable within natural constraints. In the case of neutrons, oxygen has different isotopes, which are different versions of oxygen that maintain their number of protons, but change their number of neutrons. In our scientific observations, oxygen has either 8, 9, or 10 neutrons. Now, in terms of electrons, oxygen should contain 8 electrons in order to be isoelectric, which is a way of saying the electrons equal the number of protons, rendering no charge to the oxygen atom, and this is considered the most natural state of the oxygen atom (you can “add”/”subtract” electrons by high energy collisions with particle accelerators, but that’s more artificial, and depending on the reference point, oxygen can “gain” electrons during molecular bonding).