Counting Subatomic Particles in the 23Na+ Ion

Easy

Problem

For the sodium ion 23Na+ (atomic number Z = 11), determine the number of protons, neutrons, and electrons.

Given

Nuclide: 23Na+
Atomic number of sodium: Z = 11
Mass number: A = 23
Ion charge: +1 (one electron lost)

Find

The numbers of protons, neutrons, and electrons in 23Na+.

Principle

The atomic number Z fixes the proton count and, for a neutral atom, the electron count. The mass number A is protons plus neutrons, so neutrons = A - Z. A charge of +q means q electrons were lost (or -q means gained), shifting only the electron count — protons and neutrons are untouched by ionization.

Formula

p = Z,\quad n = A - Z,\quad e = Z - q

protons = Z ; neutrons = A - Z ; electrons = Z - charge

Solution

Protons: p = Z = 11.
Neutrons: n = A - Z = 23 - 11 = 12.
Electrons in a neutral Na atom would be 11. The +1 charge means one electron was lost: e = 11 - 1 = 10.
Result: 23Na+ has 11 protons, 12 neutrons, and 10 electrons.

11 protons, 12 neutrons, 10 electrons.

Unit check

Particle counts are integers — any fractional or non-integer result would signal an arithmetic error. The three values also self-check: protons + neutrons = 23 = A, and protons - electrons = 1 = the ion charge.

What this means physically

Sodium loses one electron to become Na+, reaching the stable electron configuration of neon. Counting subatomic particles this way is the foundation for writing ion formulas and understanding why metals form cations with predictable charges.

Common mistake

Students give the ion 12 electrons (treating it as neutral sodium) or 11 neutrons (subtracting the charge). The charge only shifts the electron count, and neutrons come from mass number minus atomic number — the charge never enters that step.