how does one determine the number of neutrons, protons, electrons and mass number of an element?

Question

I know I learned this at some point...
I only have one for each, one of those fill-in chart type things.

Answer 1

This is not as difficult as it sounds.

1) The number of protons is the same as the atomic number. In fact, that is the definition of "atomic number."

2) In an atom the number of electrons = number of protons. This is only for neutral atoms! Ions are another thing. To get the number of electrons for an ion you must take the atomic number and then subtract the charge of the ion. Remember that if you subtract a negative charge you end up adding - just like negative numbers in math.

3) Neutrons must be determined by a little math, too. Neutrons = mass number - atomic number.

EX: Li
Li is element # 3. This tells us that it has 3 protons. Since there is no + or - charge written next to the Li, this must be an atom. In an atom the number of electrons in equal to the number of protons so it has 3 electrons. The mass of Li is rounded off to 7. That means there are 7 - 3 = 4 neutrons.

EX: Na 1+
Na is element # 11. This tells us there are 11 protons. This has a 1+ charge, so it is a sodium ion. To find the number of electrons you must subtract: atomic # - charge ( 11 - 1+ = 10). That means it has 10 electrons. To get the neutrons we also must do math. The mass of Na rounds off to 23. That means that atomic mass - atomic number = neutrons ( 23 - 11 = 12). There are 12 neutrons in Na 1+

Answer 2

Atomic number of an element refers to the number of protons.

In neutral state, the number of electrons is equal to the number of protons, so at this state, number of electrons is also equal to the atomic number.

Mass Number of an elements means the total of # of protons and neutrons. So when you substract atomic number from mass number you get number of neutrons.

Answer 3

Protons = atomic number
Electrons = # protons = atomic number (if it's a neutral atom)
Neutrons = mass number - atomic number