Assign oxidation states in boric acid, H3BO3.
H is +1 (x3 = +3), O is -2 (x3 = -6). For the sum to be zero, boron must be +3. Notice this is bookkeeping — boric acid is a covalent molecule.
What Is the Charge of Boron?
Boron commonly forms B3+ in introductory ionic compounds.
Boron carries a +3 assignment in compounds like B2O3 and BF3, but there is no genuine B3+ ion floating in any solution. Boron is a metalloid that bonds covalently; the +3 is an oxidation state used for bookkeeping.
| Element | Boron |
|---|---|
| Symbol | B |
| Atomic number | 5 |
| Common ionic charge | +3 |
| Common ions | B3+ |
Visual reference
Boron element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
What Boron's electrons actually do
Boron's three valence electrons (2s2 2p1) would need enormous energy to strip away completely — the sum of its first three ionization energies is prohibitive for such a small atom. Instead boron shares its three electrons, which is why borates and boranes are covalent frameworks rather than salt lattices.
Where intuition fails with Boron
Predicting that boron forms B3+ salts the way aluminum forms Al3+ salts. Aluminum, one row down, is large enough to exist as a real cation in solution; boron is not. Same group, different reality.
Worked example: B in a formula problem
B3+ in real compounds
BCl3
Boron chloride
B3+ balances chloride ions.
B2O3
Boron oxide
Boron can form oxides where total positive and negative charge balances.
Questions students ask about boron
What is the charge of boron in borax?
Borax is Na2B4O7·10H2O. Sodium is +1 and oxygen -2; solving gives boron an average of +3, consistent with its usual assignment.
Why is BF3 called electron-deficient?
Boron in BF3 has only six electrons around it instead of eight. That empty orbital makes BF3 hungry for electron pairs — a textbook Lewis acid — which is different from having a positive ionic charge.
Can boron be negative?
In metal borides such as MgB2 boron takes a negative oxidation state, and the borohydride ion BH4- carries an overall -1. These are advanced cases; +3 covers the standard problems.
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.