Hybridization of Orbitals What Proof Exists for Hybridization? Bonding Chemistry We have studied electron configuration notation and the sharing of electrons in the formation of covalent bonds. 2s and 2p hybrid orbital Orbitals Methane is a simple natural gas. Its molecule has a carbon atom at the center with four hydrogen atoms covalently bonded around it. Structure Of Molecules Lets look at a molecule of methane, CH4. Sp2 Hybridized Carbon ground state configuration What is the expected orbital notation of carbon in its ground state? (Hint: How many unpaired electrons does this carbon atom have available for bonding?) Can you see a problem with this? Carbon’s Bonding Problem You should conclude that carbon only has TWO electrons available for bonding. That is not not enough. What is taking place in order that carbon may form four bonds? Carbon’s Empty Orbital The first thought that chemists had was that carbon promotes one of its 2s electrons… …to the empty 2p orbital. However, they quickly recognized a problem with such an arrangement… Three of the carbon-hydrogen bonds would involve an electron pair in which the carbon electron was a 2p, matched with the lone 1s electron from a hydrogen atom. This would mean that three of the bonds in a methane molecule would be identical, because they would involve electron pairs of equal energy. But what about the fourth bond…? The fourth bond is between a 2s electron from the carbon and the lone 1s hydrogen electron. Such a bond would have slightly less energy than the other bonds in a methane molecule. This bond would be slightly different in character than the other three bonds in methane. This difference would be measurable to a chemist by determining the bond length and bond energy. But is this what they observe? The simple answer is, “No”. Chemists have proposed an explanation – they call it Hybridization. Hybridization is the combining of two or more orbitals of nearly equal energy within the same atom into orbitals of equal energy. Measurements show that all four bonds in methane are equal. Thus, we need a new explanation for the bonding in methane. In the case of methane, they call the hybridization sp3, meaning that an s orbital is combined with three p orbitals to create four equal hybrid orbitals. These new orbitals have slightly MORE energy than the 2s orbital and slightly LESS energy than the 2p orbitals. 1s 2sp3 2sp3 2sp3 2sp3 Hybrid Orbitals Here is another way to look at the sp3 hybridization and energy profile…sp3 While sp3 is the hybridization observed in methane, there are other types of hybridization that atoms undergo. These include sp hybridization, in which one s orbital combines with a single p orbital. This produces two hybrid orbitals, while leaving two normal p orbitals sp Hybrid Orbitals Another hybrid is the sp2, which combines two orbitals from a p sublevel with one orbital from an s sublevel. One p orbital remains unchanged. sp2 Hybrid Orbitals Exclusion Warning An understanding of the derivation and depiction of these orbitals is beyond the scope of this course and the AP Exam. Current evidence suggests that hybridization involving d orbitals does not exist, and there is controversy about the need to teach any hybridization. Until there is agreement in the chemistry community, we will continue to include sp, sp2, and sp3 hybridization in the current course.
Hybridisation / Hybridization (sp, sp2, sp3) Chemical Bonding beryllium chloride benzene methane
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