Carbon, ground-state electron configuration

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Here, the bonding between carbon atoms is briefly reviewed fuller accounts can be found in many standard chemistry textbooks, e.g., [1]. The carbon atom [ground state electronic configuration (ls )(2s 2px2py)] can form sp sp and sp hybrid bonds as a result of promotion and hybridisation. There are four equivalent 2sp hybrid orbitals that are tetrahedrally oriented about the carbon atom and can form four equivalent tetrahedral a bonds by overlap with orbitals of other atoms. An example is the molecule ethane, CjH, where a Csp -Csp (or C-C) a bond is formed between two C atoms by overlap of sp orbitals, and three Csp -Hls a bonds are formed on each C atom. Fig. 1, Al. 

We would normally write the electronic ground state electron configuration of a carbon atom as ls-2s 2p-. Despite the intellectual activity that has gone into defining mythical valence states for carbon atoms in different bonding situations, no one would include a d-orbital in the description of ground state carbon. 

Lets look at the ground state electron configuration and orbital diagram of carbon (6C) which is the first element in group 4A. 

The benzene molecule contains a ring of six carbon atoms around which six delocalized jt-electrons can circulate. An adaptation of the free-electron model (FEM) for a cyclic molecule predicts a ground-state electron configuration which we can write as Itt as shown in Fig. 6.1. 

The leftmost carbon atom in the structure is sp hybridized, and the other two carbon atoms are sp hybridized. The atoms in the molecule are located on a single straight line, with the exception of the three hydrogen atoms on the leftmost carbon atom, which point outward toward three of the vertices of a tetrahedron. There is a cr bond between each pair of bonded atoms. The p and py orbitals on carbon atoms 2 and 3 combine to form two TT orbitals and two rr orbitals only the former are occupied in the ground-state electron configuration. 

The ground-state electronic configuration of carbon is ls22s22p. 12py1. 

Carbon is a typical main group element due to its properties. It is a nonmetal with the ground state electron configuration [He]2s 2p. The electronegativity of 2.55 on the Pauling scale is quite close to that of adjacent elements in the periodic table, for example, P (2.1), B (2.0), or S (2.5). The first energy of ionization is... 

You may be surprised to learn that carbon forms four covalent bonds since you know that carbon has only two unpaired electrons in its ground-state electronic configuration (Table 1.2). But if carbon were to form only two covalent bonds, it would not complete its octet. Now we need to come up with an explanation that accounts for carbon s forming four covalent bonds. 

Methane. The carbon-atom ground-state electron configuration ls 2s 2p has two unpaired electrons and would seem to indicate a valence of 2. To get the well-known tetravalence of carbon, we assume that a 2s electron is promoted to the vacant 2p orbital, giving the configuration ls 2s2p. If we then assume one bond is formed with the 2s electron and three bonds are formed with the 2p electrons, the bonds are not all equivalent as they are known to be. Hence Pauling proposed that the 2s and 2p functions be linearly combined to form hybridized sp atomic orbitals, of the form... 

The ground state electronic configuration of allyl radical is Pi -HOMO ( Pi) of this radical has opposite sign on the terminal lobes (Ci symmetry). Suprafacial [1,3] hydrogen shift under thermal condition is forbidden because there is no question of inversion at this atom, which is bonded to the carbon atom through its spherically symmetrical Ir-orbital. Antarafacial [1,3] hydrogen shift is allowed only by the principles of orbital symmetry. The transition state is a highly contorted species and the reaction is forbidden because of the steric inhibition involved in such a process. 

In discussing the physical and chemical properties of an element, chemists often focus on the outermost shell of its atoms, because electrons in this shell are the ones involved in the formation of chemical bonds and in chemical reactions. We call outer-shell electrons valence electrons, and we call the energy level in which they are found the valence shell. Carbon, for example, with a ground-state electron configuration of, has four... 

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