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LIVE LAB 13 • CHEMICAL BONDING
Explore bridge and banana bonding from foundation to advanced level through rotatable 3D models of B₂H₆, Be₂H₄, Al₂Cl₆, Be₂Cl₄, polymeric BeCl₂, I₂Cl₆ and Al₂(CH₃)₆.
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ACTUAL LAB PREVIEWQUICK START
COMPLETE CONCEPT GUIDE
Master the complete bridge-bonding sequence: identify the electron-deficient centre, decide whether the bridge supplies a lone pair, count each multicentre unit correctly, and compare structure, orbital overlap, bond length, strength and planarity.
In B₂H₆ and Be₂H₄, one electron pair is delocalised over three nuclei. The two curved B–H–B regions in diborane are commonly called banana bonds; each bridge is one three-centre two-electron unit, not two ordinary bonds.
In Al₂Cl₆, Be₂Cl₄, polymeric BeCl₂ and I₂Cl₆, a bridging chlorine lone pair aligns with an electron-poor acceptor direction. The model compares the original shared pair with the donated pair across each three-centre bridge.
Compare terminal and bridge contacts, simultaneous bridge formation, bridge angles, maximum coplanar atoms, hybridisation labels and the absence of a separate central atom–central atom bond where the multicentre model applies.
Move from hydrogen bridges in diborane and beryllium hydride to chlorine bridges in aluminium and beryllium halides, then examine carbon bridges in Al₂(CH₃)₆ to connect the same electron-counting logic across compound classes.
BRIDGE & BANANA BONDING FAQ
A banana bond is the curved three-centre two-electron B–H–B bonding region in B₂H₆. One electron pair is spread over two boron atoms and one bridging hydrogen atom.
A 3c–2e bridge contains one electron pair shared across three centres. A 3c–4e bridge contains four electrons across three centres and commonly includes lone-pair donation from a bridging atom such as chlorine toward an electron-poor centre.
Important examples include B₂H₆, Be₂H₄, Al₂Cl₆, Be₂Cl₄, solid polymeric BeCl₂, I₂Cl₆ and Al₂(CH₃)₆, together with their electron counts, geometry, bridge type and bond comparisons.
MOLECULE-BY-MOLECULE GUIDES
Open a focused structure guide, then use the shared 3D lab to rotate the complete molecule and compare bridge formation.
Diborane banana bonding
Open structure guide →Beryllium hydride bridge bonding
Open structure guide →Aluminium chloride bridge bonding
Open structure guide →Beryllium chloride dimer bonding
Open structure guide →Polymeric beryllium chloride
Open structure guide →Iodine trichloride dimer bonding
Open structure guide →Trimethylaluminium methyl bridges
Open structure guide →Connect this lab with related chemistry topics and choose the depth that fits your current studies.
STUDENT DISCUSSION
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Electron density in a multicentre bridge is distributed across three atoms, so each individual bridge contact generally has lower bond order and is often longer than the corresponding terminal two-centre bond.
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