chemcheat

BF3 Lewis Structure

Boron trifluoride · A gas used as a Lewis acid catalyst in organic synthesis.

Lewis structure of BF3 (Boron trifluoride)The bond dipoles are all the same size and the shape places them symmetrically around the central B, so they cancel exactly.BFFF

The BF3 Lewis structure has 24 valence electrons, drawn as three B–F bonds, with nine lone pairs in total. The central B is sp2 hybridized, which makes it a trigonal planar molecule with a bond angle of 120 degrees. BF3 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.

Calculated properties

Calculated properties of BF3
Total valence electrons 24
Bonding electrons 6 (3 shared pairs)
Nonbonding electrons 18 (9 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 67.804 g/mol

How to draw the BF3 Lewis structure

  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 7 (F) = 24 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, 18 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 20, has 18, 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. Fill in the lone pairs

    Every electron not in a bond sits as a lone pair on an atom. Each atom takes exactly what it needs to finish its shell - there is no choice left at this point.

    F1: 3, F2: 3, F3: 3 (18 electrons)

  7. 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

  8. 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

  9. 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

  10. 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 BF3 polar or nonpolar?

BF3 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–F 1.94 largely ionic
Why this molecule gets set as a problem: Boron stops at six electrons. Forcing an octet here would be worse chemistry.

Common questions

How many valence electrons does BF3 have?

BF3 has 24 valence electrons. 6 of them are in bonds and 18 sit in lone pairs.

What is the molecular geometry of BF3?

BF3 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 BF3?

The bond angle in BF3 is 120 degrees. That is the ideal trigonal planar angle, and nothing distorts it here.

What is the hybridization of BF3?

The central B in BF3 is sp2 hybridized. Steric number 3 means 3 orbitals have to be mixed, which is exactly what sp2 gives you.

Is BF3 polar or nonpolar?

BF3 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.