In chemistry , orbital hybridisation or hybridization is the concept of mixing atomic orbitals into new hybrid orbitals with different energies, shapes, etc. Hybrid orbitals are very useful in the explanation of molecular geometry and atomic bonding properties and are symmetrically disposed in space.
Energy Level Diagrams for sp Orbitals
Chemist Linus Pauling first developed the hybridisation theory in to explain the structure of simple molecules such as methane CH 4 using atomic orbitals. In reality, methane has four bonds of equivalent strength separated by the tetrahedral bond angle of Pauling explained this by supposing that in the presence of four hydrogen atoms, the s and p orbitals form four equivalent combinations or hybrid orbitals, each denoted by sp 3 to indicate its composition, which are directed along the four C-H bonds.
It gives a simple orbital picture equivalent to Lewis structures. Hybridisation theory is an integral part of organic chemistry , one of the most compelling examples being Baldwin's rules. For drawing reaction mechanisms sometimes a classical bonding picture is needed with two atoms sharing two electrons.
Orbitals are a model representation of the behaviour of electrons within molecules.
In heavier atoms, such as carbon, nitrogen, and oxygen, the atomic orbitals used are the 2s and 2p orbitals, similar to excited state orbitals for hydrogen.
Hybrid orbitals are assumed to be mixtures of atomic orbitals, superimposed on each other in various proportions. Hybridisation describes the bonding atoms from an atom's point of view. For a tetrahedrally coordinated carbon e. Carbon's ground state configuration is 1s 2 2s 2 2p 2 or more easily read:.
The carbon atom can use its two singly occupied p-type orbitals, to form two covalent bonds with two hydrogen atoms, yielding the singlet methylene CH 2 , the simplest carbene.
The carbon atom can also bond to four hydrogen atoms by an excitation or promotion of an electron from the doubly occupied 2s orbital to the empty 2p orbital, producing four singly occupied orbitals. The energy released by the formation of two additional bonds more than compensates for the excitation energy required, energetically favouring the formation of four C-H bonds.
Quantum mechanically, the lowest energy is obtained if the four bonds are equivalent, which requires that they are formed from equivalent orbitals on the carbon.
A set of four equivalent orbitals can be obtained that are linear combinations of the valence-shell core orbitals are almost never involved in bonding s and p wave functions,  which are the four sp 3 hybrids. Other carbon compounds and other molecules may be explained in a similar way. For example, ethene C 2 H 4 has a double bond between the carbons.
What are sp, sp2, sp3 orbitals?
In sp 2 hybridisation the 2s orbital is mixed with only two of the three available 2p orbitals, usually denoted 2p x and 2p y. The third 2p orbital 2pz remains unhybridised. The hydrogen—carbon bonds are all of equal strength and length, in agreement with experimental data.
The chemical bonding in compounds such as alkynes with triple bonds is explained by sp hybridisation. In this model, the 2s orbital is mixed with only one of the three p orbitals,.
Hybridisation helps to explain molecule shape , since the angles between bonds are approximately equal to the angles between hybrid orbitals, as explained above for the tetrahedral geometry of methane. Other examples are given in the table below.
Orbitals: Crash Course Chemistry #25
Nonetheless, molecules such as Ta CH 3 5 with sd 4 hybridisation adopt a square pyramidal shape. Hybridisation is often presented for main group AX 5 and above, as well as for many transition metal complexes, using the hybridisation scheme first proposed by Pauling.
In this notation, d orbitals of main group atoms are listed after the s and p orbitals since they have the same principal quantum number n , while d orbitals of transition metals are listed first since the s and p orbitals have a higher n. Thus for AX 6 molecules, sp 3 d 2 hybridisation in the S atom involves 3s, 3p and 3d orbitals, while d 2 sp 3 for Mo involves 4d, 5s and 5p orbitals. In , Magnusson published a seminal work definitively excluding the role of d-orbital hybridisation in bonding in hypervalent compounds of second-row period 3 elements, ending a point of contention and confusion.
Part of the confusion originates from the fact that d-functions are essential in the basis sets used to describe these compounds or else unreasonably high energies and distorted geometries result. Also, the contribution of the d-function to the molecular wavefunction is large. These facts were incorrectly interpreted to mean that d-orbitals must be involved in bonding.
For transition metal centres, the d and s orbitals are the primary valence orbitals, which are only weakly supplemented by the p orbitals. In light of computational chemistry , a better treatment would be to invoke sigma bond resonance in addition to hybridisation, which implies that each resonance structure has its own hybridisation scheme. For main group compounds, all resonance structures must obey the octet 8-electron rule. For transition metal compounds, the resonance structures that obey the duodectet electron rule  suffice to describe bonding, with optional inclusion of d m sp n resonance structures.
Although ideal hybrid orbitals can be useful, in reality most bonds require orbitals of intermediate character. This requires an extension to include flexible weightings of atomic orbitals of each type s, p, d and allows for a quantitative depiction of bond formation when the molecular geometry deviates from ideal bond angles. The amount of p-character is not restricted to integer values; i.
The hybridisation of bond orbitals is determined by Bent's rule : "Atomic s character concentrates in orbitals directed towards electropositive substituents". For molecules with lone pairs, the bonding orbitals are isovalent sp x hybrids. For example, the two bond-forming hybrid orbitals of oxygen in water can be described as sp 4. The shapes of molecules with lone pairs are:.
In such cases, there are two mathematically equivalent ways of representing lone pairs. They can be represented by orbitals of sigma and pi symmetry similar to molecular orbital theory or by equivalent orbitals similar to VSEPR theory.
Hybrid Atomic Orbitals
For hypervalent molecules with lone pairs, the bonding scheme can be split into a hypervalent component and a component consisting of isovalent sp x bond hybrids. The hypervalent component consists of resonant bonds using p orbitals.
The table below shows how each shape is related to the two components and their respective descriptions. Hybridisation of s and p orbitals to form effective sp x hybrids requires that they have comparable radial extent. The hybridisation of atoms in chemical bonds can be analysed by considering localised molecular orbitals, for example using natural localised molecular orbitals in a natural bond orbital NBO scheme.
A similar trend is seen for the other 2p elements. For heavier p block elements this assumption of orthogonality cannot be justified.
Sp type hybrid atomic orbitals spdf
These deviations from the ideal hybridisation were termed hybridisation defects by Kutzelnigg. One misconception concerning orbital hybridisation is that it incorrectly predicts the ultraviolet photoelectron spectra of many molecules. While this is true if Koopmans' theorem is applied to localised hybrids, quantum mechanics requires that the in this case ionised wavefunction obey the symmetry of the molecule which implies resonance in valence bond theory.
A linear combination of these four structures, conserving the number of structures, leads to a triply degenerate T 2 state and a A 1 state. Bonding orbitals formed from hybrid atomic orbitals may be considered as localized molecular orbitals, which can be formed from the delocalised orbitals of molecular orbital theory by an appropriate mathematical transformation. For molecules in the ground state, this transformation of the orbitals leaves the total many-electron wave function unchanged.
The hybrid orbital description of the ground state is therefore equivalent to the delocalised orbital description for ground state total energy and electron density, as well as the molecular geometry that corresponds to the minimum total energy value.
Molecules with multiple bonds or multiple lone pairs can have orbitals represented in terms of sigma and pi symmetry or equivalent orbitals. Different valence bond methods use either of the two representations, which have mathematically equivalent total many-electron wave functions and are related by a unitary transformation of the set of occupied molecular orbitals.
For multiple bonds, the sigma-pi representation is the predominant one compared to the equivalent orbital bent bond representation. In contrast, for multiple lone pairs, most textbooks use the equivalent orbital representation. An analogous consideration applies to water one O lone pair is in a pure p orbital, another is in an sp x hybrid orbital. From Wikipedia, the free encyclopedia. Redirected from Orbital hybridization. This is the latest accepted revision , reviewed on 9 December Mixing superposition of atomic orbitals in chemistry.
See also: tetrahedral molecular geometry. See also: trigonal planar molecular geometry. See also: linear molecular geometry. Main article: Hypervalent molecule. Main article: Isovalent hybridisation. Main articles: Localized molecular orbitals and Natural bond orbital. Main article: Sigma-pi and equivalent-orbital models.
Application of results obtained from the quantum mechanics and from a theory of paramagnetic susceptibility to the structure of molecules", Journal of the American Chemical Society , 53 4 : —, doi : Pauling The Nature of the Chemical Bond 3rd ed. Organic Chemistry 1st ed. Oxford University Press. Orgo Made Simple. Retrieved 23 June Chemistry Annotated Instructors Edition 4th ed. Prentice Hall.
Cambridge: Cambridge University Press. Angew Chem Int Ed Engl. Molecular Orbitals of Transition Metal Complexes. Oxford: Oxford University Press. Rossi; Roald.
Hoffmann Inorganic Chemistry. Hoffmann; Barbara F. Beier; Earl L. Muetterties; Angelo R. Rossi A molecular orbital exploration of structure, stereochemistry, and reaction dynamics".