Boron ground state electronic configuration

Let s look at the ground state electron configuration and orbital diagram of Boron (5B) which is the first element of group 3A. 

Write down the ground state electronic configuration of boron, and give a set of quantum numbers that uniquely defines each electron. 

Next, consider the BF3 (boron trifluoride) molecule, which has trigonal planar geometry based on VSEPR and experimental evidence. The ground state electron configuration of B is [He]2s 2p, so it has only one unpaired valence electron. 

We can do a similar analysis of the bonds and the trigonal-planar geometry of boron trifluoride (BF3). The ground-state electron configuration of the B atom is [He]2t 2/ . containing just... 

Although the boron atom (with electron configuration Is2 2s2 2p ) has three valence electrons, only one of them is unpaired in the ground state. 

The theoretical basis of this approach is not immediately obvious what, for example, is the meaning of the fractional occupation numbers To establish its status, let us take a simple example, the boron atom with electron configuration ls 2s 2p and a ground state. If we use a 1-determinant wavefunction with A = %, B = 2, W = 2p then the energy expression will be... 

Electron configurations, as they are used in this book, provide information about the first two quantum numbers, n and 1. (Electron configurations may also reflect the third quantum number, mi, but this notation goes beyond the scope of this chemistry course.) The electron configuration below represents a boron atom in its ground state. 

Because of its small size and s p electronic ground state, boron is unique among the elements with its predilection for sp hybridized trigonal planar coordination. However, given the acidic character of the unfilled octet, hybridization to tetrahedral BO4 configurations is also important. These simple elementary units may be found as discrete anions but more often they are utilized as building blocks of more complicated ions or as part of extended two and three-dimensional stmctures. 

Next we turn to the BHj molecule, in which the three B-H bonds are coplanar, and the H B-H angle is 120°, The electronic configuration of the boron atom in the ground state is ls 2s 2p, and hybridization can occur only after promotion of an electron from the 2s orbital to a 2p orbital to give a ls 2s 2p configuration. Three equivalent hybrid sp orbitals can then be constructed as follows ... 

Silicon Hybridization. Hybridization of the silicon atom occurs in a manner similar to the tetragonal hybridization of the carbon atom to form a configuration of four 3sp orbitals also arranged in a r lar tetrahedron.1 1 Boron Hybridization. As shown in Table 7.1, the boron atom has only one valence electron in the ground state (2p ). Yet boron is never monovalent but always trivalent as the atom is hybridized.l 11 1 However, unlike the tetragonal hybridization of earbon and silicon, the boron hybrid ization is trigonal (sjp). It occurs as follows ... 

There are 24 valence electrons iij BFs [7 from each fluorine (Zs lp ), 3 from the boron (2r 2fi)]. Placing these electrons in the most stable molecular orbitals, we obtain a ground-state configuration ... 

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