How to find electrons on periodic table

How many protons, electrons and neutrons are in an atom of krypton, carbon, oxygen, neon, silver, gold, etc...?

Table of Contents Show

Covered in other articles
Vocabulary:
How to find the Atomic Number
Finding the Number of Protons
Finding the Number of Neutrons
Finding the Number of Electrons
Summary Table
Worlds Best Periodic Table
Further Reading

To find the number of protons, electrons and neutrons in an atom, just follow these easy steps:

Step 1 - Gather Information

The first thing you will need to do is find some information about your element. Go to the Periodic Table of Elements and click on your element. If it makes things easier, you can select your element from an alphabetical listing.

Use the Table of Elements to find your element's atomic number and atomic weight. The atomic number is the number located in the upper left corner and the atomic weight is the number located on the bottom, as in this example for krypton:

Step 2 - The Number of Protons is...

The atomic number is the number of protons in an atom of an element. In our example, krypton's atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus.

The interesting thing here is that every atom of krypton contains 36 protons. If an atom doesn't have 36 protons, it can't be an atom of krypton. Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of krypton creates an atom of bromine.

Step 3 - The Number of Electrons is...

By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.

Electrons are arranged around atoms in a special way. If you need to know how the electrons are arranged around an atom, take a look at the 'How do I read an electron configuration table?' page.

An atom can gain or lose electrons, becoming what is known as an ion. An ion is nothing more than an electrically charged atom. Adding or removing electrons from an atom does not change which element it is, just its net charge.

For example, removing an electron from an atom of krypton forms a krypton ion, which is usually written as Kr+. The plus sign means that this is a positively charged ion. It is positively charged because a negatively charged electron was removed from the atom. The 35 remaining electrons were outnumbered by the 36 positively charged protons, resulting in a charge of +1.

Step 4 - The Number of Neutrons is...

The atomic weight is basically a measurement of the total number of particles in an atom's nucleus. In reality, it isn't that clean cut. The atomic weight is actually a weighted average of all of the naturally occurring isotopes of an element relative to the mass of carbon-12. Didn't understand that? Doesn't matter. All you really need to find is something called the mass number. Unfortunately, the mass number isn't listed on the Table of Elements. Happily, to find the mass number, all you need to do is round the atomic weight to the nearest whole number. In our example, krypton's mass number is 84 since its atomic weight, 83.80, rounds up to 84.

The mass number is a count of the number of particles in an atom's nucleus. Remember that the nucleus is made up of protons and neutrons. So, if we want, we can write:

Mass Number = (Number of Protons) + (Number of Neutrons)

For krypton, this equation becomes:

84 = (Number of Protons) + (Number of Neutrons)

If we only knew how many protons krypton has, we could figure out how many neutrons it has. Wait a minute... We do know how many protons krypton has! We did that back in Step 2! The atomic number (36) is the number of protons in krypton. Putting this into the equation, we get:

84 = 36 + (Number of Neutrons)

What number added to 36 makes 84? Hopefully, you said 48. That is the number of neutrons in an atom of krypton.

The interesting thing here is that adding or removing neutrons from an atom does not create a different element. Rather, it creates a heavier or lighter version of that element. These different versions are called isotopes and most elements are actually a mixture of different isotopes.

If you could grab atoms of krypton and count the number of neutrons each one had, you would find that most would have 48, others would have 47, some would have 50, some others would have 46, a few would have 44 and a very few would have 42. You would count different numbers of neutrons because krypton is a mixture of six isotopes.

In Summary...

For any element:

Number of Protons = Atomic Number

Number of Electrons = Number of Protons = Atomic Number

Number of Neutrons = Mass Number - Atomic Number

For krypton:

Number of Protons = Atomic Number = 36

Number of Electrons = Number of Protons = Atomic Number = 36

Number of Neutrons = Mass Number - Atomic Number = 84 - 36 = 48

In this tutorial, you will learn how to find and calculate the number of protons, neutrons, and electrons in an atom or element. In addition, you will learn about the different subatomic particles. If you enjoy this tutorial, be sure to check out our others!

Covered in other articles

Vocabulary:

Protons: Positively charged subatomic particles located in the nucleus of an atom.
Neutrons: Neutrally charged subatomic particles located in the nucleus of an atom.
Electrons: Negatively charged subatomic particles located in orbitals surrounding the nucleus.
Atomic Mass: A weighted average of the number of neutrons and protons present for all isotopes.
Atomic Number: Number of protons present in an atom.
Element: A pure substance that cannot be broken down into a simpler substance by chemical means

How to find the Atomic Number

The atomic number of an element is simply the number of protons in its nucleus. The easiest way to find the atomic number, is to look on a periodic table, the atomic number is in the upper left corner, or is the largest number on the square.

Finding the Number of Protons

The number of protons in an atom is equal to the atomic number of the element. For example, let’s use oxygen. According to the periodic table, oxygen has the atomic number eight. The atomic number is located above the element’s symbol. Since oxygen has an atomic number of eight, there must be eight protons total. Moreover, the number of protons never changes for an element.

Finding the Number of Neutrons

The number of neutrons in an atom can be calculated by subtracting the atomic number from the atomic mass. Both of these numbers can be found on the periodic table. The atomic number is listed above the symbol of the element whereas the mass number is placed below. Let’s keep using oxygen as our example. Its atomic mass is 15.999 atomic mass units (amu) and its atomic number is 8. When we subtract 8 from 15.999, we will get 8. Also, it should be noted that the number of neutrons for an element may vary. Some elements have isotopes, which have different masses and therefore different numbers of neutrons.

Finding the Number of Electrons

The number of electrons in an atom is equal to the atomic number of an element, for neutrally charged species. This means the number of electrons and the number of protons in an element are equal. Therefore, the number of electrons in oxygen is 8. Moreover, since these two subatomic particles, electrons and protons, have opposite charges, they cancel out and keep the atom neutral.

Summary Table

Number of Protons =	Atomic Number
Number of Neutrons =	Atomic Mass- Atomic Number
Number of Electrons =	Atomic Number

In this chemical reaction, known as the Briggs-Rauscher reaction, the number of protons and neutrons in each atom do not change. Electrons, however, are moving between atoms, causing different ions to form and causing the color changes. Please subscribe to our YouTube channel, lots more amazing videos are on the way!