How do you calculate the atom of a element?

Answer 1

The only way I can make this question make sense is to assume you're trying to ask "how do you calculate the number of protons and neutrons in an atom?"

The name or symbol of the element will tell you the number of protons (though, if you didn't already know that, you'll likely need to look it up on a Periodic Table). For example, a carbon atom has 6 protons.

To figure out the number of neutrons, you'll need to know the Atomic Mass number. This is usually given either as a superscript to the left of the element symbol, or as a number following the name or symbol of the element (often separated by a dash). For example, "carbon 13" and "C-13" both have an atomic mass number of 13. If you don't see a number ... you're in trouble (unless the element is identified as deuterium or tritium; these have 1 proton and 1 neutron, or 1 proton and 2 neutrons, respectively). You can look up the atomic mass on a periodic table, but that will be an AVERAGE value. For example, the atomic mass given for chlorine will be somewhere in the vicinity of 35.453. That's because the two most common isotopes of chlorine are chlorine-35 and chlorine-37, in about a 3 to 1 ratio. You can't identify the number of neutrons unless you know specifically which isotope is meant.

Assuming you do know the atomic mass number; it's also the number of nucleons. Subtract the number of protons from the atomic mass number, and what's left over is the number of neutrons.

So: carbon-13 has 6 protons (because it's carbon) and 7 neutrons (because 13-6 = 7).