How can you find the number of protons and electrons and neutrons in an atom or ion?

Answer 1

Number of protons = Atomic number

Number of electrons = Atomic number minus the charge (if it is ion)

Number of neutrons = Mass number minus Atomic number

• Number of Protons:

Look at the Periodic Table. Each element is assigned a number called the atomic number -- it is usually written in large on the periodic table. That number tells you the number of protons in the nucleus of each element. The atomic number is always the same as the number of protons. The number of protons in the nucleus uniquely identifies an element.

• Number of Electrons:

The number of electrons in an element can change. For a neutral atom (net charge of zero), the number of protons is exactly equal to the number of electrons. So the number of electrons is also the same as the atomic number.

However, it is possible to remove electrons and not change the identity of an element. These are called ions. The charge on the ion tells you the number of electrons -- the number of electrons is the atomic number minus the charge on the ion if it's an ion. If the charge is positive, subtract that number from the atomic number to get the number of electrons (with a positively charged ion, you will then have less electrons than protons).

If the charge is negative, subtract the charge (but note you are subtracting a negative number, which is the same as adding the magnitude of the charge to the atomic number (with a negatively charged ion, you with then have more electrons than protons).

• Number of Neutrons:

The number of neutrons in an element can also vary, and if two atoms of the same element have different numbers of neutrons, then they are called isotopes. To figure out how many neutrons are in the nucleus, you must know the mass number. Note that you cannot determine the number of neutrons for an element, only for one isotope of that element -- so you have to know which isotope you are being asked about.

Usually, a specific isotope is written like this: silicon-30 or carbon-12 or aluminum-26. It can also be written like this though, when using the symbol for the element instead of its full name: 30Si or 12C or 26Al. The number is called the mass number, and the mass number is equal to the sum of the number of protons plus the number of neutrons.

So if you know the mass number and you know the atomic number (if you know the name of the element, that tells you the atomic number because each element has only one atomic number), to find the number of neutrons, subtract the mass number from the atomic number.

Here are some examples:

• The element hydrogen (H) has atomic number of 1, so it has one proton in the nucleus, and one electron. The hydrogen ion (H+) has zero electrons, and the hydrogen ion (H-) has 2 electrons. Most hydrogen atoms don't have any neutrons (these are written 1H), but there exists an isotope called deuterium (also 2H) which has one neutron, and another isotope called tritium (also 3H) which has 2 neutrons.

• The element fluorine (F) has atomic number 9, so it has nine protons. The neutral atom also has 9 electrons, but F is commonly found as a negative ion F-, which has 10 electrons. The most common isotope of fluorine has 10 neutrons, and so it has a mass number of 19, and is written Fluorine-19 or 19F. There also exists another isotope, fluorine-18 or 18F, which only has 9 neutrons, but this isotope is not stable.

Answer 2

1.You get the number of protons and electrons from the atomic number (number on top of element symbol).

2. You find the number of neutrons in one particular isotope of an element by subtracting the atomic number with the isotope mass number, (number behind the isotope's name).

For complete explanation: cf. 'Related links' down this page

Answer 3

You can look up individual elements online, for example in the Wikipedia.

The number of protons is the atomic number. For example, carbon is element #6; that means it has 6 protons.

The number of electrons - assuming a neutral atom - is equal to the number of protons. Note that an atom can temporarily gain or lose electrons.

The number of neutrons varies for the same element, that is, different atoms in one element can have a different number of neutrons. Look up information about isotopes, for example, "isotopes of carbon". Example: carbon-14 is a radioactive isotope of carbon. The number 14 is the total Atomic Mass, i.e., protons + neutrons. Since we already know that it has 6 protons, subtract this from 14, to get 8 neutrons. The most common form of carbon is carbon-12, which of course has 6 protons and 6 neutrons.

Answer 4

Take a look at a periodic table. For an atom of a given element, the number of protons is the same as the atomic number, or the number at the top of the square. The number of electrons is the same as the number of protons in a neutral atom, where the number of positively-charged protons is the same as the number of negatively-charged electrons. If the question does not specifically state whether the atom is neutral or an ion, assume that it is neutral.

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The number of protons (and therefore electrons) has been determined by the comparative nuclear charge of a given element, which is directly determined by the number of positively-charged particles (protons) in the nucleus.

Answer 5

On the periodic table each element has an atomic weight. The atomic weight is the number of protons and neutrons in the nucleus. Since most atoms have the same number of these just divide in half to find the protons. Every atom also has the same number of electrons as protons so the numbers should be the same. To check make sure, the atomic number should be the same as this.

Answer 6

the number of protons is just the atomic number and to find electrons just subtract the atomic number to the charge, if it's an ion.

Answer 7

Search the atomic number of the element.

atomic number = number of protons

number of neutrons=mass number- nunber of protons