# How many protons are in an isotope of sodium with a mass number of 25?

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• Zirp
Lv 7
1 year ago

Like others said, Sodium (Na) atoms have 11 protons.

Even if you don know that, you know it couldn't have been more than 12, as atoms with more protons than neutrons don't exist

• 1 year ago

The number of protons is what determines an element. It is called the atomic number (as opposed to the atomic mass = protons + neutrons).

The number of protons determines the number of electrons in orbit around a neutral atom, and the properties of electrons determines the behavior of the electrons - this determines how the element will chemically behave.

11 protons = sodium, regardless of the mass number of the atom.

Na-25 (the isotope of sodium with a mass of 25) has 11 protons (because it is sodium). Therefore it has 14 neutrons, in order for the mass to equal 25 (11 + 14)

Na-23 is the stable isotope of sodium, with 11 protons and 12 neutrons. It is the sodium we find in nature.

Na-22 (11 + 11) and Na-24 (11+13) are both radioactive; they are produced artificially.

• 1 year ago

Protons ......

ANY isotope of sodium has 11 protons!

The mass number has nothing to do with it. If you want the number of neutrons, then subtract the atomic number (Z) from the mass number (A).

Na-25 ................ 25 -11 = 14 neutrons

A couple of things to remember.

1. ALL atoms are isotopes. There are no atoms which are not isotopes.

2. Mass number is always an integer: the sum of protons + neutrons

3. Mass number is never the atomic mass rounded off to a whole number.

4. Atomic mass is the weighted average of the masses of the naturally occurring isotopes of an element.