BF3 Lewis Structure, Characteristics: 13 Facts You Should Know


This article contains about BF3 lewis structure, shape, valence electrons, resonance, and many more detailed facts.

In the BF3 lewis structure, the shape of the molecule is planar trigonal having a bond angle of 1200. The central B atom is sp2 hybridized. Three F atoms are present at the three corners of the trigonal moiety. Due to having a vacant site in B it can accept electrons or lone pairs and behaves as lewis acid.

Three F atoms and B are present in the same plane. The molecule is nonpolar due to zero dipole moment. The B-F bond length is near around 130 pm. It is isoelectronic with carbonate anion.

Some important facts about BF3

BF3 is gaseous in its physical state and it is a colorless gaseous molecule having a pungent odor. It is a very toxic gas living being. The boiling point and melting point of BF3 are 172.8 K and 146.3 K respectively.

In the laboratory, boron trifluoride can be prepared by the reaction of hydrogen fluoride and boron oxide.

B2O3 + 6HF = 2BF3 + 3H2O

Due to its electron-deficient site, it can participate in many organic reactions as an electrophile.

1.    How to draw the BF3 lewis structure

Lewis structure is also known as lewis dot structure and it helps to find the number of electrons involved in bond formation, number of lone pairs, shape bond angle, and binding mode of a molecule.

In the BF3 lewis structure, we should consider the valence electrons of B and I. B has 3 valence electrons and F has 7 valence electrons. Among them, F Uses only one electron for bond formation so the remaining 6 electrons exist as lone pairs. B has no lone pair.

Then we should identify the central atom by electronegativity. Here B is less electronegative than F so B is the central atom and three F atoms are present at three corners. The molecule is neutral so required for adding or substracting electrons. Now B and three F atoms are connected via single bonds only to satisfy their octet.

2.    BF3 lewis structure shape

The whole electron density lies in the BF3 lewis structure on the central B atom only.

The structure is trigonal planar with B at a central position of the trigonal moiety and three F atoms at the three corners of that triangle. The lone pairs are assigned to the three F atoms only at the corner position.

3.    BF3 valence electrons

In the BF3 lewis structure, three F atoms are attached to central B via single bonds only.

BF3 lewis structure
BF3 Valence Electrons

The electronic configuration of B is [He]2s22p1, so there are there electrons present at the valence shell and three electrons are involved in bond formation with three F atoms. But the electronic configuration of F is [He]2s22p5. So, in the outermost shell F has seven electrons.

So total number of valence electrons in BF3 molecule is (7*3) + 3 = 24

4.    BF3 lewis structure formal charge

The formal charge of a particular atom or molecule is calculated by assuming the same electronegativity for all atoms.

The common formula for calculation of formal charge is, F.C. = Nv – Nl.p. -1/2 Nb.p.

Where Nv is the number of electrons in the valence shell, Nl.p is the number of electrons in the lone pair, and Nb.p  is the total number of electrons that are involved in the bond formation only.

In the BF3 lewis structure, we need to calculate formal charges separately for B and F atoms.

 For B = 3-0-(6/2) = 0

For F = 7-6-(2/2)= 0

So, we see that the formal charge of B, as well as F, is 0. It is also reflected that the molecule is neutral and has no charge over it.

5.    BF3 lewis structure lone pairs

Lone pairs are those electrons present in the valence shell but not involved in the bond formation.

BF3 Lone Pairs

From the electronic configuration of B, it is evident that it has 3 electrons in its valence shell and all the electrons are involved in the bond formation with three F atom. So, B is lack of lone pair in Boron trifluoride. But the electronic configuration of F we can see that it has 7 electrons in its valence shell as it is a VIIA group element. Among 7 electrons only one electron is involved with the B for bond formation. So, the rest of the six electrons exist as 3 pairs of lone pairs over each F atom.

So, the total number of lone pairs in boron trifluoride is 0+(6*3) =18

6.    BF3 lewis structure octet rule

Each atom in a molecule tries to complete its octet by donating electrons from the valence shell or accepting electrons in the valence shell and gaining the nearest noble gas configuration.

B is a p block group 13th element, so it has 3 electrons in its outermost shell. By forming a bond with three f atoms B shares one electron of each F atom in hybridization. But it gains only 6 electrons in its valence shell ( two in s orbital and four in p orbital) but it gains stability due to zero formal charge and it is a violation of the octet rule, So, B is electro deficient.

But in the case of F, it has seven electrons in its valence shell and shares one electron with B, and completes its octet fully.

So, in the BF3 lewis structure, we can see the valence electron in bond formation will be 3 from B and 1 from each F atom. So, the number of total electrons involved in the bond formation of boron trifluoride is  3+(3*1) =6 which is a violation of the octet rule.

7.    BF3 lewis structure bond angle

The bond angle of a molecule is the angle where two or more atoms make during the formation of a molecule.

BF3 Bond Angle

From the VSEPR (Valence Shell Electron Pair Repulsion) theory, a molecule having a trigonal planar shape has a bond angle of 1200. From the BF3 lewis structure, it is evident that the shape of the molecule is trigonal planar so the bond angle between F-B-F is 1200. Due to the smaller size of the F atom, lone pair repulsion is minimized here. So, the angle is ideal 1200 and has no requirement of deviation.

8.    BF3 lewis structure resonance

Resonance is a hypothetical concept of a molecule for the delocalization of its electron clouds in different skeleton forms.

BF3 Resonating Structure

Structures II, III, and IV are equivalent and have a greater contribution to resonance as they contain more covalent bonds. If the number of covalent bonds are equal for more than one structure than we should check the negative charge is on electronegative atom or positive charge on electropositive atom.

9.    BF3 hybridization

Hybridization is also a hypothetical concept to determine the mode of bonding of a covalent molecule by mixing orbitals of two or more atoms to get hybrid orbitals.

The hybridization of any molecule is calculated by the formula

H = 0.5(V+M-C+A), where H= hybridization value, V is the number of valence electrons in the central atom, M = monovalent atoms surrounded, C=no. of cation, A=no. of the anion.

In the BF3 lewis structure, the central B has three valence electrons (one in s and two in p orbital) and there are three F atoms present in the surrounding.

So, the hybridization value for boron trifluoride is = ½(3+3+0+0)= 3 (sp2)

StructureHybridization value      State of hybridization of central atom             Bond angle
Linear  2sp /sd / pd     1800
Planner trigonal3   sp2  1200
Tetrahedral   4sd3/ sp3       109.50
Trigonal bipyramidal  5sp3d/dsp3      900 (axial), 1200(equatorial)
Octahedral6sp3d2/ d2sp    900
Pentagonal bipyramidal7  sp3d3/d3sp3          900,720

 From the above table, we can say that if the hybridization value is 3 then the mode of hybridization will be sp2 which means one s and two p orbitals are involved in this hybridization. Here s and p orbital of B and only the P orbital of F are involved.

BF3 Hybridization

Boron is group 13th element so in the ground state, the electronic configuration of Boron is [He]2s22p1.P orbital can accumulate a maximum of 6 electrons. To complete the p orbital, we need 3 more electrons. F is from the halogen family and group 17th so the electronic configuration is [He]2s22p5. To complete the octet of B it needs 5 more electrons, and to complete the octet of Fluorine it needed one electron.

Now by the mixing of orbital in hybridization each F atoms share one electron with B and complete the octet but for B three electrons come from 3 F but the octet is not complete as shown in the box diagram, so it is a violation of octet rule.

So here one s and two P orbitals are mixing and giving sp2 hybrid orbital. From the table, we can see that sp2 hybridized molecule has a 1200 bond angle and its shape will be trigonal planar which is also reflected in VSEPR theory.

 In the hybridization, we consider only the sigma bond, the π bond is not involved in the hybridization.

10.    BF3 solubility

Though BF3 is a covalent molecule it can soluble in water by the process of hydrolysis.

Actually, in the BF3 lewis structure, the octet of B is not completed and there is a vacant p orbital available in B so here it can take the lone pair of oxygen from a water molecule and react with water and get slowly hydrolyzed.

BF3-H2O Adduct

It can also be soluble in many organic and nonpolar solvents as well.

11.    Is BF3 ionic?

According to Fajan’s rule, no molecule is 100% ionic or covalent.

The size of the B is very small so it can easily polarize any anion by its ionic potential but the size of F is also small so it cannot be easily polarizable. But due to ionic potential and Fajan’s rule of polarization of Bf3 lewis structure, we can say that BF3 contains little amount of ionic character.

12.    Is BF3 polar or nonpolar?

The polarity of a molecule depends on the dipole moment.

BF3 Dipole Moment

Dipole moment always acts from electropositive atom to electronegative atom. Here dipole moment acts from B to F atom. But in the BF3 lewis structure, shape of the molecule is planar trigonal, so the resultant dipole moment of B to two F atoms is exactly opposite the dipole moment from B to the third F atom. So, both dipole moments minimize the net dipole moment which is zero for the BF3 molecule.

Due to zero dipole moment, the BF3 molecule is non-polar.

13.    Is BF3 acidic or basic?

BF3 molecule acts as strong lewis acid, it can accept electrons in its vacant orbital.

From the BF3 lewis structure, we can see that B is not complete in its octet and there is a vacant p orbital present after the sp2 hybridization in B. So, B is electron deficient here and it can accept electron or lone pairs from the respective molecule or atoms and can act as lewis acid. The electronegativity of three F atoms increases the chances of accepting electrons and it behaves as strong lewis acid.

Even BF3 reacts with water to form hydroboric acid.

    Is there any chance of back bonding in BF3?

It is due to the presence of the 3 electronegative F atoms that the sigma electron density from central B is being dragged away.

Thus, the B center becomes less electropositive. In order to reduce the electron deficiency at the B, 3 F atoms donate π electron density simultaneously towards the central B leading to the formation of pπ– pπ back bonding.

pπ– pπ Back Bonding.

Compare the acidity of BF3, BCl3, BBr3, BI3

BI3 has higher lewis acidity than others and the order of the acidity decrease from right to left.

BI3>BBr3>BCl3>BF3

It is due to the larger size of I the orbital mismatch is here greater. So, the back bonding is lesser here so the vacant orbital of B can easily accept electrons from any lewis base.

The bond length of B-F in BF3 is expected to be shorter. Why?

In the BF3 lewis structure, the bond length is 131.8 pm but the experimental data shows that the bond length is 130 pm.

The reason behind the shorter bond length is the back π bonding between B and F. Due to this back bonding there is a partial double bond character will be observed between B and F. so the bond length is decreased.

Conclusion

From the above discussion about the BF3 molecule, we can conclude that B violated the octet rule here but gained stability due to zero formal charge. The shape and bond angle of the molecule can predict from  VSEPR theory as well as hybridization. BF3 can behave as strong lewis acid due to the vacant orbital of B and there is a chance of back bonding between B and F. The molecule is nonpolar by its zero dipole moment.

                                                                                                       

Biswarup Chandra Dey

Chemistry is not all about reading line by line and memorize, it is a concept to understand in easy way and here I am share with you the concept about chemistry which I learn because knowledge is worth to share it.

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