chemcheat

BH3 Lewis Structure

Borane · A boron hydride that pairs up as diborane on its own, and reacts with alkenes in hydroboration.

Lewis structure of BH3 (Borane)The bond dipoles are all the same size and the shape places them symmetrically around the central B, so they cancel exactly.BHHH

The BH3 Lewis structure has 6 valence electrons, drawn as three bonds to hydrogen, with zero lone pairs in total. The central B is sp2 hybridized, which makes it a trigonal planar molecule with a bond angle of 120 degrees. BH3 is nonpolar: the bond dipoles are all the same size and the shape places them symmetrically around the central B, so they cancel exactly.

At least one atom does not reach a full octet in this structure.

BH3 molecular geometry

BH3 molecular geometry: trigonal planarBHHH

Trigonal planar, from 3 electron domains on the central B: 3 bonded atoms (AX3). The electron geometry is trigonal planar. Wedges point toward you, hashed wedges away. Every shape in the VSEPR chart →

Calculated properties

Calculated properties of BH3
Total valence electrons 6
Bonding electrons 6 (3 shared pairs)
Nonbonding electrons 0 (0 lone pairs)
Lone pairs on B 0
Electron domains (steric number) 3
VSEPR notation AX3
Electron geometry trigonal planar
Molecular geometry trigonal planar
Bond angle 120°
Hybridization sp2
Polarity nonpolar
Formal charges all zero
Resonance structures none
Molar mass 13.834 g/mol

B Boron 3 valence e− H Hydrogen 3 atoms, 1 valence e− each

How to draw the BH3 Lewis structure

The reasoning at each step

  1. Count the valence electrons

    Add up the outer-shell electrons every atom brings. That total is the budget for the whole structure - every line and every dot has to come out of it, and nothing may be added.

    3 (B) + 3 x 1 (H) = 6 valence electrons

  2. Choose the central atom

    B is the least electronegative atom here, so it takes the centre. Hydrogen is never central: it can only form one bond.

  3. Join everything with single bonds first

    Every connection starts as one shared pair. Draw them all before worrying about double bonds - the arithmetic in the next step is what tells you where the double bonds have to go.

    3 bonds x 2 = 6 electrons used, 0 left

  4. Work out how far short you are

    Add up what every atom still needs to fill its shell - eight electrons for most atoms, two for hydrogen - minus what its single bonds already give it. Compare that with the electrons you have left. The difference decides everything that follows.

    needs 2, has 0, short by 2

  5. Accept an incomplete octet

    You are 2 electrons short, and the only way to close the gap would be a double bond to a halogen - which is not something these atoms do. B stays below eight electrons instead. That is real chemistry, not a mistake.

    B: 6 electrons

  6. Check the central atom

    B ends up with 6 electrons, short of an octet, which is correct for this molecule.

    B: 6 bonding + 0 nonbonding = 6

  7. Check the formal charges

    Formal charge is valence electrons, minus lone-pair electrons, minus the number of bonds. Every atom here comes out at zero, which is the sign of a good structure.

    all formal charges = 0

  8. Work out the shape

    Count the electron domains on B: 3 bonded groups. A double or triple bond still counts as one domain, because it points in one direction. That gives trigonal planar electron geometry; ignore the lone pairs and the atoms themselves sit in a trigonal planar arrangement.

    steric number 3 -> sp2 -> trigonal planar, bond angle 120

  9. Decide whether it is polar

    The bond dipoles are all the same size and the shape places them symmetrically around the central B, so they cancel exactly.

    dipoles cancel -> nonpolar

Is BH3 polar or nonpolar?

BH3 is nonpolar. The bond dipoles are all the same size and the shape places them symmetrically around the central B, so they cancel exactly.

BondElectronegativity differenceCharacter
B–H 0.16 nonpolar covalent
Why this molecule gets set as a problem: Boron stops at six electrons, which is exactly why borane grabs any lone pair it meets.

Common questions

How many valence electrons does BH3 have?

BH3 has 6 valence electrons. 6 of them are in bonds and 0 sit in lone pairs.

What is the molecular geometry of BH3?

BH3 is a trigonal planar molecule. The central B has 3 bonded groups, a steric number of 3, which gives trigonal planar electron geometry and a trigonal planar molecule.

What is the bond angle in BH3?

The bond angle in BH3 is 120 degrees. That is the ideal trigonal planar angle, and nothing distorts it here.

What is the hybridization of BH3?

The central B in BH3 is sp2 hybridized. Steric number 3 means 3 orbitals have to be mixed, which is exactly what sp2 gives you.

Is BH3 polar or nonpolar?

BH3 is nonpolar. The bond dipoles are all the same size and the shape places them symmetrically around the central B, so they cancel exactly.

How this page was produced. The formula was parsed, the connectivity resolved (central atom), and every bond-order arrangement enumerated and scored on octet satisfaction, formal charge and where that charge sits. The structure above is the winner. Bond angles, hybridization and the polarity verdict are read off the resulting geometry, not looked up.