Boron Lewis structure

An electrostatic potential map of boron trifluoride is shown. Is BF3 likely to be a nucleophile or an electrophile Draw a Lewis structure for BF3, and explain your answer. 

The Lewis structure of the product, a white molecular solid, is shown in (32). In this reaction, the lone pair on the nitrogen atom of ammonia, H3N , can be regarded as completing boron s octet in BF3 by forming a coordinate covalent bond. 

Compounds of boron and aluminum may have unusual Lewis structures in which... 

Borazine, B3N3Hft, a compound that has been called inorganic benzene because of its similar hexagonal structure (but with alternating B and N atoms in place of C atoms), is the basis of a large class of boron—nitrogen compounds. Write its Lewis structure and predict the composition of the hybrid orbitals used by each B and N atom. 

Many gallium compounds have structures that are similar to those of the corresponding aluminum and boron compounds. Draw the Lewis structure and describe the shape of GaBr4. ... 

C21-0047. Boron nitride (BN) is a planar covalent solid analogous to graphite. Write a portion of the Lewis structure and describe the bonding of boron nitride, which has alternating B and N atoms. 

It must be emphasized that the formulation of three-center T-bonds provides a qualitative (not merely incremental) improvement in the accuracy of the natural Lewis-structure description of diborane. Because a three-center orbital is intrinsically more mathematically flexible than a two-center orbital, the description of any molecule is seemingly improved by employing three-center in place of two-center NBOs. However, for most non-boron molecules this improvement would be quite negligible (e.g., less than 0.1% for ethane, whose two-center Lewis-structure... 

Q O The molecules BF3 and NH3 are known to undergo a combination reaction in which the boron and nitrogen atoms of the respective molecules join together. Sketch a Lewis structure of the molecule that would be expected to be formed from this reaction. Would the product molecule be expected to be more or less reactive than the starting materials Give a reason for your answer. 

This suggests that the appropriate Lewis structure is the one which lacks a boron-boron bond, rather than the one which shows the two borons directly bonded. 

All Br0nsted-Lowry acids are Lewis acids, but in practice, the term Lewis acid is generally reserved for Lewis acids that don t also fit the Bronsted-Lowry definition. The best way to spot a Lewis acid-base pair is to draw a Lewis dot structure of the reacting substances, noting the presence of lone pairs of electrons. (We introduce Lewis structures in Chapter 5.) For example, consider the reaction between ammonia (NH3) and boron trifluoride (BFj) ... 

Trimethylbortme Dih).2 We may assume that the methyl groups will have their usual configuration found in organic compounds. The Lewis structure of (CHj)jB will place six electrons in the valence shell of the boron atom, and in order that the-electron pairs be as fair apart as possible, the methyl groups should be located at the comers of an equilateral triangle. This results in sp2, or trigonal Ur), hybridization for the bcron atom (Fig. 6.1b). 

A boron trifluoride molecule, BF3, has the Lewis structure shown in (5). There are three bonding pairs attached to the central atom and no lone pairs. According to the VSEPR model, as illustrated in Fig. 3.4, the three bonding pairs, and the fluorine atoms they link, lie at the corners of an equilateral triangle. Such a structure is trigonal planar, and all three F—B—F angles are 120° (6). 

The LE model is a simple but very successful model, and the rules we have used for Lewis structures apply to most molecules. To implement this model we have relied heavily on the octet rule. So far we have treated molecules for which this rule is easily applied. However, inevitably, cases arise where the importance of an octet of electrons is called into question. Boron, for example, tends to form compounds in which the boron atom has fewer than eight electrons around it—it does not have a complete octet. Boron trifluoride (BF3), a gas at normal temperatures and pressures, reacts very energetically with molecules such as water and ammonia that have available lone pairs. The violent reactivity of BF3 with electron-rich molecules occurs because the boron atom is electron-deficient. Boron trifluoride has 24 valence electrons. The Lewis structure that seems most consistent with the properties of BF3 is... 

An important observation supporting the need for resonance in the LE model is that there are only three different structures of dichlorobenzene (C6H4C12). How does this fact support the need for the concept of resonance Borazine (B3N3H6) has often been called inorganic benzene. Draw Lewis structures for borazine. Borazine is a six-membered ring of alternating boron and nitrogen atoms. 

Elements in groups 2A and 3A of the periodic table, such as beryllium and boron, do not have enough valence electrons to form an octet in a neutral molecule. Lewis structures for BeH2 and BF3 show that these atoms have only four and six electrons, respectively, around the central atom. There is nothing we can do about this There simply aren t enough electrons to form an octet. 

Although the rules presented in Chapter 1 for obtaining Lewis structures work most of the time, there are situations in which these approximations are not applicable. Boron is an element that displays unusual bonding properties in a number of its compounds. 

Although crystal structures of other bimolecular complexes of carbonyls with boronic Lewis acids have not been reported, a number of intramolecular chelates have been detected in the solid state. In all these cases boron is found to lie in the direction of the carbonyl lone pair with no more than 11 distortion away from the best plane of the carbonyl group. The average B—O bond length is 1.581 0.019 A and the B—O—C angle lies between 112 and 119. ... 

You may have to try several Lewis structures until you get one in which all of the atoms, except hydrogen, beryllium, and boron, obey the octet rule. 

Now think about what happens when the central atom is surrounded by three shared pairs. Look at the Lewis structure for BF3, which has boron, an example of an atom that does not always obey the octet rule. 

Draw the Lewis structures for boron, nitrogen, and phosphorus. 

D.K. STRAUB, Lewis structures of boron compounds involving multiple bonding. J. Chem. Educ., 72, 494 (1995). 

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