Hydrogen atom orbital overlap

Each lobe of the sp orbital containing one-electron overlap head-on carbon atoms and translational repetition of this tetragonal C-C cluster makes diamond. The three tetrahedral arms of orbital can also be terminated by hydrogen atoms that overlap head-on. If terminated by hydrogen, the tetrahedral C-H cluster makes the CH molecule of gas methane (Fig. 4.4). 

The formation of bonding molecular orbitals by an overlap of atomic orbitals applies not only to the Is orbitals of hydrogen, but also to other atomic orbitals. When the atomic orbitals overlap along the axis of the bond, a covalent bond, called a sigma (a) bond, results. This is normally referred to as end-on overlap. Some examples of the formation of a bonds from overlapping atomic orbitals are shown in the diagrams. 

When N atomic orbitals overlap, they form N molecular orbitals. In molecular hydrogen, where we are building LCAO-MOs from two atomic orbitals, we expect two molecular orbitals. In the second molecular orbital, the two atomic orbitals interfere destructively where they overlap. This orbital has the form... 

A covalent bond is formed between two atoms together in a molecular structure. It is formed when atomic orbitals overlap to produce a molecular orbital. For example, the formation of a hydrogen molecule (H2) from two hydrogen atoms. Each hydrogen atom has a half-filled Is atomic orbital and when the atoms approach each other, the atomic orbitals interact to produce two MOs (the number of resulting MOs must equal the number of original atomic orbitals) ... 

Orbital diagram of the methyl cation. The methyl cation is similar to BH3. The carbon atom is a bonded to three hydrogen atoms by overlap of its sp2 hybrid orbitals with the s orbitals of hydrogen. A vacant p orbital lies perpendicular to the plane of the three C —H bonds. 

Fig. 1.1 Overlap of hydrogen atom orbitals to form (a) a bonding orbital, and (b) an antibonding orbital, with energies as shown in (c).

Show how a hydrogen Is atomic orbital and a fluorine 2p atomic orbital overlap to form bonding and antibonding MOs in the hydrogen fluoride molecule. Are they cr or 77 MOs ... 

Describe what atomic orbitals overlap to produce a carbon-hydrogen bond in CH4. 

When two hydrogen l5 orbitals overlap out of phase with each other, an antibonding molecular orbital results (Figure 2-7). The two wave functions have opposite signs, so they tend to cancel out where they overlap. The result is a node (actually a nodal plane) separating the two atoms. The presence of a node separating the two nuclei usually indicates that the orbital is antibonding. 

For an opposing view, see Devarajan, D., Gustafson, S. J., Bickelhaupt, F. M., Ess, D. H. (2015). Is There a Need to Discuss Atomic Orbital Overlap When Teaching Hydrogen-Halide Bond Strength and Acidity Trends in Organic Chemistry Journal of Chemical Education, 92(2), 286-290. 

The Hiickel MO method assumes that the a and n systems can be treated independently and then considers only the n system. The extended Hiickel theory (EHT), developed by Hoffmann, considers all of the valence electrons in the system, but it does not deal with the core electrons (those in orbitals below the valence shell). ° The EHT wave function is then written as a linear combination of functions describing each type of valence orbital on each atom in the structure. For hydrocarbons, the EHT wave fimctions include the 2s and all three 2p atomic orbitals of carbon as well as the Is orbitals of hydrogen atoms. The overlap integrals (S,y) are computed, whereas they were ignored in HMO theory. The elements of the secular determinant are assigned a value... 

The geometry of the hydrogen atoms in methane is tetrahedral, so a tetrahedral model is used. Each hydrogen atom will overlap all three p-orbitals and also the 2s-orbital, which occupies space at some distance from the carbon nucleus, to form the bond. A hydrogen atom will not approach so close to carbon... 

To get a sense of Ihe approach taken in MO theory, we will begin with the simplest molecule the hydrogen molecule, H2. We will use the two Is atomic orbitals (one on each H atom) to "build" molecular orbitals for the H2 molecule. Wljenever two atomic orbitals overlap, two molecular orbitals form. Thus, the overlap of the Is orbitals of two hydrogen atoms to form H2 produces two MOs (Figure 9.33 ). 

There are two different ways in which we can linearly combine two 1j hydrogen atomic orbitals. The first is to add them together (Fig. 2-5). It is easy to see from this figure that an electron in MO I will spend most of its time in the overlap region between the nuclei Ho and Hj. This maximizes the attractive force between the electron and the two nuclei therefore an electron in this MO is more... 

The other linear combination is formed by subtraction of one of the two hydrogen Is orbitals from the other (Fig. 2-7). This type of MO has a node in the region between the two nuclei. Thus an electron in MO II will never be found halfway between the two nuclei instead it will be mainly confined to space outside the overlap region. An electron in MO II is less stable than in an isolated Ir hydrogen atomic orbital, and we therefore say that II is antibonding. The antibonding MO also has cylindrical symmetry and thus is [Pg.41]

Consider the bond formed between the two hydrogen atoms in molecular hydrogen. This bond is the result of the overlap of two atomic orbitals s orbitals), each of which is occupied by one electron. According to MO theory, when two atomic orbitals overlap, they cease to exist. Instead, they are replaced by two molecular orbitals, each of which is associated with the entire molecule (Figure 1.15). 

---