Calculating the mass number of an element is pretty easy once you understand it!

The mass number is an important idea in chemistry. It tells us how many protons and neutrons are in the nucleus (the center) of an atom.

Here’s a simple way to calculate it:

1. Find the Atomic Number: First, look for the atomic number of the element on the periodic table. The atomic number shows the number of protons in the nucleus. You can usually find it at the top of the element's box.

2. Count the Neutrons: Next, you need to find out how many neutrons are in the nucleus. This number isn't always given, but there's a simple way to discover it:

   • Use this formula:
     Number of Neutrons = Mass Number - Atomic Number
   • If you know the mass number (we will discuss this next), you can easily find the number of neutrons.

3. Calculate the Mass Number: To find the mass number, use this formula:
   Mass Number = Number of Protons + Number of Neutrons
   Since you already have the atomic number (which tells you the number of protons), you just need the number of neutrons.

4. Example with Oxygen: Let’s say you are looking at oxygen, which has an atomic number of 8. This means oxygen has 8 protons. In its most common form, it also has 8 neutrons. So:
   Mass Number = 8 (protons) + 8 (neutrons) = 16

5. Different Isotopes: Remember, different isotopes of the same element can have different mass numbers because they have different numbers of neutrons. For example, oxygen-16 has 8 neutrons, but oxygen-18 has 10 neutrons.

In summary, understanding how to calculate the mass number using the atomic number and the number of neutrons is an essential skill in chemistry. Once you get this idea, it becomes easier to understand atoms and the elements around us!