3-1-4 Multiple bonds in Be and B compounds
3-1-4 Multiple bonds in Be and B compounds
3-1-4 Multiple bonds in Be and B compounds
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3-1-2 Exp<strong>and</strong>ed shells<strong>Be</strong>yond the oct rule, an option limited to elementsof the third <strong>and</strong> higher periods is to use d orbitalsfor this expansion (ClF 3 & SF 6 ).
3-1-3 Formal charge
3-1-4 <strong>Multiple</strong> <strong>bonds</strong> <strong>in</strong> <strong>Be</strong> <strong>and</strong> B <strong>compounds</strong>A few molecules, such as <strong>Be</strong>F 2 , <strong>Be</strong>Cl 2 , & BF 3 ,seem to require multiple <strong>bonds</strong> to satisfy the octetrule for <strong>Be</strong> & B, even though we do not usuallyexpect multiple <strong>bonds</strong> for fluor<strong>in</strong>e & chlor<strong>in</strong>e.
B 2 H 6 HBHBHHHHDiborane
3-2 Valence shell electron pair repulsion theoryIt provides a method for predict<strong>in</strong>g the shape ofmolecules, based on the electron pair electrostaticrepulsion. Steric number (SN = m + n) for AX m E n .
Electronegativity
Electronegativity & bond angles : many bondangles can be expla<strong>in</strong>ed by either electronegativityor size argument.(1) electronegativity(2) size(3) lone-pair effect
(II)(I)
(I) The atom with larger electronegativity drawsthe electrons toward itself & away from the centralatom, reduc<strong>in</strong>g the repulsive effect of thosebond<strong>in</strong>g electrons.
As a result, the lone pair effect is relatively larger& forces smaller bond angles. The same result isobta<strong>in</strong>ed if size is considered; as the size of theouter atom <strong>in</strong>creases <strong>in</strong> th F < Cl < Br < I series,the angle <strong>in</strong>creases.
(II) When the central atom’s size <strong>in</strong>creases (bondlength <strong>in</strong>creased), the lone pair is more important<strong>and</strong> a smaller bond angle is favored due to arelatively larger repulsive effect.For the molecules conta<strong>in</strong><strong>in</strong>g H, neither the electronegativitynor the size argument work well.
3-2-4 Lig<strong>and</strong> close-pack<strong>in</strong>gThe lig<strong>and</strong> close-pack<strong>in</strong>g (LCP) model uses thedistances between the outer atoms <strong>in</strong> molecules asa guide. For a series of molecules with the samecentral atom, the nonbonded distances betweenthe outer atoms are consistent, but the bond angles<strong>and</strong> lengths change.
3-4 Hydrogen bond<strong>in</strong>g
A prote<strong>in</strong> α helix
The pleated sheet arrangement