Linear molecular
geometry
In chemist ry, t he linear molecular geomet ry describes t he geomet ry around a cent ral at om
bonded t o t wo ot her at oms (or ligands) placed at a bond-angle of 180°. Linear organic
molecules, such as acet ylene (HC≡CH), are oft en described by invoking sp orbit al hybridizat ion
for t heir carbon cent ers.
Linear molecular geometry
Examples
CO2, XeF2
Point group
D∞h
Coordination number
2
Bond angle(s)
180°
μ (Polarity)
0
Structure of beryllium fluoride (BeF2), a compound with a linear geometry at the beryllium atom.
Two sp orbitals
According t o t he VSEPR model (Valence Shell Elect ron Pair Repulsion model), linear geomet ry
occurs at cent ral at oms wit h t wo bonded at oms and zero or t hree lone pairs (AX2 or AX2E3) in
t he AXE not at ion. Neut ral AX2 molecules wit h linear geomet ry include beryllium fluoride (F−Be−F)
wit h t wo single bonds,[1] carbon dioxide (O=C=O) wit h t wo double bonds, hydrogen cyanide
(H−C≡N) wit h one single and one t riple bond. The most import ant linear molecule wit h more t han
t hree at oms is acet ylene (H−C≡C−H), in which each of it s carbon at oms is considered t o be a
cent ral at om wit h a single bond t o one hydrogen and a t riple bond t o t he ot her carbon at om.
Linear anions include azide (N−3) and t hiocyanat e (SCN−), and a linear cat ion is t he nit ronium ion
(NO+2 ).[2]
Linear geomet ry also occurs in AX2E3 molecules, such as xenon difluoride (XeF2)[3] and t he
t riiodide ion (I −3) wit h one iodide bonded t o t he t wo ot hers. As described by t he VSEPR model,
t he five valence elect ron pairs on t he cent ral at om form a t rigonal bipyramid in which t he t hree
lone pairs occupy t he less crowded equat orial posit ions and t he t wo bonded at oms occupy t he
t wo axial posit ions at t he opposit e ends of an axis, forming a linear molecule.
See also
See also
AXE met hod
Molecular geomet ry
References
1. Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 43.
ISBN 978-0-13-039913-7.
2. Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford:
Butterworth-Heinemann. ISBN 0-7506-3365-4.
3. Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 47.
ISBN 978-0-13-039913-7.
External links
Indiana Universit y Molecular St ruct ure Cent er (ht t ps://web.archive.org/web/2001122419335
5/ht t p://www.iumsc.indiana.edu/IUMSC/)
Int eract ive molecular examples for point groups (ht t p://www.st aff.ncl.ac.uk/j.p.goss/symmet r
y/Molecules_ l3d.ht ml)
Molecular Modeling (ht t ps://web.archive.org/web/20080120023822/ht t p://chemlab.t ruman.ed
u/CHEM121Labs/MolecularModeling1.ht m)
Animat ed Trigonal Planar Visual (ht t p://int ro.chem.okst at e.edu/1314F97/Chapt er9/3BP.ht ml)
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