Protons, neutrons, and electrons are three main particles that make up an atom. As the name suggests, protons are positively charged, electrons are negatively charged, and neutrons are uncharged (they are neutral). Electrons have very little mass, while protons and neutrons have almost identical masses. You can easily find the number of protons, neutrons, and electrons in an atom using information from the periodic table.
Steps
Part 1 of 2: Calculate Protons, Electrons, and Neutrons
Step 1. Obtain a periodic table of elements
The periodic table is a chart that organizes elements by atomic structure. It is color-coded and assigns each item a 1, 2, or 3 letter abbreviation. Other elemental information that it also includes is weight and atomic number.
You can find a periodic table online or in a chemistry book
Step 2. Find your element on the periodic table
The elements are arranged in the periodic table by atomic number and are separated into three main groups: metals, nonmetals, and metalloids (semimetals). Other elemental groupings are the alkali metals, halogens, and noble gases.
- Using groups (columns) or periods (rows) can make an item easier to locate in the table.
- You can also search the table for the element's symbol if you don't know what its properties are.
Step 3. Find the atomic number of the element
The atomic number is located above the element symbol, in the upper left corner of the box. The atomic number will tell you how many protons make up a single atom of an element.
For example, boron (B) has an atomic number of 5, therefore it has 5 protons
Step 4. Determine the number of electrons
Protons are particles that are in the nucleus of an atom and have a positive charge. Electrons are particles that have a negative charge. Therefore, an element in its neutral state will have the same number of protons and electrons.
- For example, boron (B) has an atomic number of 5, therefore it has 5 protons and 5 electrons.
- However, if the element includes a positive or negative ion, then the protons and electrons will not be the same. You will have to calculate them. The number of ions will appear as a small superscript after the element.
Step 5. Find the atomic mass of the element
To find the number of neutrons, you will first have to find the atomic mass. The atomic mass of an element (also known as atomic weight) is the average mass of atoms of an element. The atomic mass can be found under the element symbol.
Make sure to round the atomic mass to the nearest whole number. For example, the atomic mass of boron is 10.811; however, you can simply round the atomic mass to 11
Step 6. Subtract the atomic number from the atomic mass
To find the number of neutrons you will have to subtract the atomic number from the atomic mass. Remember that the atomic number is the same as the number of protons, which you already identified.
In our example with boron it would look like this: 11 (atomic mass) - 5 (atomic number) = 6 neutrons
Part 2 of 2: Calculate Electrons with Ions Present
Step 1. Identify the number of ions
The number of ions in an element will appear as a small superscript next to the element. An ion is an atom that has a positive or negative charge due to the addition or removal of electrons. While the number of protons in the atom will remain the same, the number of electrons will alter in an ion.
- Since an electron has a negative charge, the ion will turn positive when you remove electrons. In turn, when you add more electrons, the ion will turn negative.
- For example, N3- has a charge of -3 while Ca2+ have a charge of +2.
- Note that this calculation is not necessary if there is no superscript ion next to the element.
Step 2. Subtract the charge from the atomic number
If an ion has a positive charge, the atom lost electrons. To calculate the remaining number of electrons, subtract the amount of extra charge from the atomic number. In the case of a positive ion, there are more protons than electrons.
- For example, Ca2+ it has a charge of +2, therefore it lost 2 electrons from its neutral state. The atomic number of calcium is 20, therefore the ion has 18 electrons.
Step 3. Add the charge to the atomic number to get the negative ions
When an ion has a negative charge, the atom gained electrons. To calculate the total number of electrons there are, simply add the amount of additional charge to the atomic number. In the case of a negative ion, there are fewer protons than electrons.
- For example, N3- It has a charge of -3, therefore it gained 3 electrons compared to its neutral state. Nitrogen's atomic number is 7, therefore this ion has 10 electrons.