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Covalent bonding is described as electron pair sharing where the orbital from two atoms are overlapped. The valence bond theory describes how bonding occurs. Atoms in a bond are able to rearrange the electrons in their valence shells to create lower energy hybrid orbitals. These hybrid orbitals can overlap with orbitals on other atoms to share electrons and form bonds. 21 Figure 3.9 Electrons with opposite spins pair and overlap their s-orbitals to form a -bond (sigma bond). The cloud has cylindrical symmetry around the internuclear axis and is spread over both nuclei. The -bond is colored blue.
22 A -bond formed from electrons in 1s and 2pz pairing. HF The two electrons are spread over the overlapped orbitals. 23 A -bond formed from electrons in two 2p-orbitals pairing. The two electrons are spread over the overlapped orbitals.
24 Hybrid Orbitals: (Valence Bond Theory)
Beryllium will form two covalent bonds with chlorine atoms. How does this occur if the valence electrons of Be are both in the 2s? (BeCl2) Let's look at the orbital filling diagram for Be.
___ ___ ___ 2p [He] 2s2 [He] 2s 25 Hybrid Orbitals: (Valence Bond Theory)
___ ___ [He] 2s2 [He] sp sp 2p .. .. : Cl -Be Cl : both bonds are sp-orbitals Created with 1 s and 1 p-orbital p- The sp hybrids have the same energy and Be has space for sharing two orbitals. 26 To make room in the 2s energy level, Be must move an electron into an empty p-orbital: HalfHalfempty P-orbital 2 RHED 27 p.312 Hybrid Orbitals: (Valence Bond Theory)
Boron will form three covalent bonds with hydrogen. (BH3) [He] 2s22p1 [He] 2s 2p (hybrid orbitals form) [He] 2s22p1 [He] sp2 sp2 sp2 2p H H -- B -- H (all of the covalent bonds are sp2 hybrid bonds) Created from 1 s and 2 p orbitals 28 2 p-orbitals pForm 3 sp2 orbitals 1 s-orbital s- 29 p.313 BF3 3 RHED 30 p.314 Hybrid Orbitals: (Valence Bond Theory)
Carbon will form four covalent bond...
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