Write the formula for sodium molybdate, a fertilizer micronutrient.
Na+ with MoO4 2- takes two sodiums: Na2MoO4. Legume crops need the Mo6+ in it to build the nitrogenase enzyme that fixes nitrogen from air.
What Is the Charge of Molybdenum?
Molybdenum commonly forms Mo4+ Mo6+ in introductory ionic compounds.
Molybdenum's two headline states are +6 — the molybdate ion MoO4 2- that plants and your own enzymes depend on — and +4 in MoS2, the slippery black solid in engine greases and modern 2D-material research.
| Element | Molybdenum |
|---|---|
| Symbol | Mo |
| Atomic number | 42 |
| Common ionic charge | +4, +6 |
| Common ions | Mo4+, Mo6+ |
Visual reference
Molybdenum element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
Where Molybdenum's charge options come from
Molybdenum is [Kr]4d5 5s1, with a half-filled d shell echoing chromium above it. All six valence electrons engage for +6 with oxygen; pairing with sulfur favors +4. Unlike chromium, molybdenum's +6 is gentle rather than aggressively oxidizing — gentle enough for biology to use.
This is a classroom reference range, not an exhaustive list of all oxidation states.
The trap in Molybdenum problems
Transferring chromium's toxicity intuition to molybdenum. Chromium +6 is a carcinogen; molybdenum +6 is an essential trace nutrient found in beans and grains. Same group and charge, opposite biological verdicts — proof that charge alone doesn't decide toxicity.
Worked example: Mo in a formula problem
Mo4+ and Mo6+ in real compounds
MoCl4
Molybdenum chloride
Mo4+ balances chloride ions.
Mo2O3
Molybdenum oxide
Molybdenum can form oxides where total positive and negative charge balances.
Questions students ask about molybdenum
What does molybdenum's charge do in the human body?
About four human enzymes hold a molybdenum atom that cycles between +4 and +6 as it processes sulfites and purines — the redox flexibility of those two states is precisely the feature biology exploits.
Why is MoS2 so slippery?
Its S–Mo–S sandwich layers (Mo at +4) bind each other only weakly, so sheets slide like cards in a deck. The lubrication is structural; no charges move.
What is 'moly steel'?
Chromoly and similar alloys include neutral molybdenum atoms that harden steel and keep it strong when hot — drill bits and bike frames alike. Metallurgy at charge 0.
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.