Zak asked in Science & MathematicsChemistry · 8 years ago

# How do I find out the number of protons, neutrons and electrons in a atom?

I mean, I have a science exam tomorrow, and I specialize in science, and I wanted to know this for sure... How do I find the number of electrons in a atom? I thought it was the atomic number is how much protons and neutrons in the atom, as in, atomic number = 1, protons = 1, neutrons = 1. and electrons were the weight, as in, atomic mass = 4, eletrons = 4. Is this correct? or am I doing this wrong? If so, Can you explain how to do it?

Relevance
• 8 years ago

number of protons: you have to know the atomic number or the name/symbol of the element. If I tell you the atomic number is 11, you know that the number of protons is 11. If I tell you the element is uranium, you look up the atomic number on a periodic table and then you know that the number of protons is 92 because that's the atomic number of uranium.

number of neutrons: you have to know the mass number (which is the sum of the protons and the neutrons) of the given isotope under question. For example, I tell you I have two isotopes of nitrogen, mass numbers of 14 and 15. How many neutrons in each? N-14 ---> 14 minus 7 = 7 and N-15 ---> 15 - 7 = 8. Notice that 7 is the atomic number of nitrogen and I used it in both subtractions.

nmber of electrons: you have to know the charge on the atom. Suppose I have an atom of magnesium and it is neutral. How many electrons? The answer is 12 because there are 12 protons (look up Mg on periodic table) and that means 12 positive charges. Since the atom is neutral, there have to be 12 negative charges, so 12 electrons. Suppose the atom of Mg has a +2 charge, how many electrons? The answer is 10. The 12 pos charges are balanced by 10 neg charges, leaving me with a +2 overall charge on the atom (which is now called an ion, since it has a charge)/

Chlorine-37 with a -1 charge. How many p, n, and e?

p = 17

n = 20

e = 18

Best wishes on the exam.

Source(s): ChemTeam
• 8 years ago

Atomic number is how many protons are in an atom. The atomic weight is the amount of protons AND neutrons.

In a neutral element, the eletrons will equal the number of protons for a neutral (or 0) charge.

For example, In carbon the atomic number is 6 and the atomic weight is 12.01. So

Protons = atomic number = 6

Neutrons = (atomic weight - atomic number) = 6

electons = atomic number (in a neutral atom) = 6

Once you get the idea, it's easy.

• TK
Lv 7
8 years ago

The atomic number can also be considered the proton number. In a neutral atom (0 charge), the protons and electrons equal each other. So the atomic number is the number of protons and also the number of electrons.

To calculate the number of neutrons, you need the mass number. The mass number minus the atomic number (number of protons) is the number of neutrons.

• Vickie
Lv 4
4 years ago

Protons and electrons 13. Neutrons 14.