Predict formulas for rubidium oxide and rubidium nitride.
Rb+ with O2- gives Rb2O; with N3- gives Rb3N. Identical patterns to sodium — group position, not atomic size, writes the formula.
What Is the Charge of Rubidium?
Rubidium commonly forms Rb+ in introductory ionic compounds.
Rubidium forms Rb+ — the alkali-metal +1, no exceptions — in compounds like RbCl and RbOH. Everything potassium does, rubidium does more violently: drop it in water and the +1 ions form with a bang.
| Element | Rubidium |
|---|---|
| Symbol | Rb |
| Atomic number | 37 |
| Common ionic charge | +1 |
| Common ions | Rb+ |
Visual reference
Rubidium element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
Why Rubidium gives up exactly one electron
Rubidium is [Kr]5s1. Its single outer electron sits in the fifth shell, farther out and more weakly held (403 kJ/mol) than potassium's — the lowest ionization energy of any stable element except cesium and francium. One easy electron out, then a krypton core no reaction can touch.
The formula slip students make with Rubidium
Overthinking rubidium problems. Some students expect a twist because the element is unfamiliar — there is none. Every rubidium formula follows the Group 1 pattern: RbF, Rb2O, Rb2SO4, Rb3PO4.
Worked example: Rb in a formula problem
Rb+ in real compounds
RbCl
Rubidium chloride
Rb+ balances chloride ions.
Rb2O
Rubidium oxide
Rubidium can form oxides where total positive and negative charge balances.
Questions students ask about rubidium
What are rubidium ions doing in atomic clocks?
Rubidium clocks watch neutral Rb atoms — a specific microwave frequency (6.83 GHz) flips their outermost electron's spin. GPS satellites carry them. Charge 0; precision comes from that lone 5s electron.
Why is rubidium more reactive than potassium if both end up 1+?
Both reach the same +1 finish line, but rubidium's outer electron starts farther from the nucleus and leaves with less prompting. Reactivity measures the ease of the trip, not the destination.
Does the body use Rb+ for anything?
It has no biological role, but Rb+ is so similar to K+ that cells absorb it readily — the basis of rubidium-82 heart-imaging scans, where the ion maps blood flow to cardiac muscle.
How do I use this charge in formulas?
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
Where this data comes from
Charges and element facts on this page are checked against the primary references below. Found an error? Email hello@periodictablewithcharges.com — corrections ship in the next content update. See how this site is edited.