തന്മാത്രാ ജ്യോമെട്രി

വിക്കിപീഡിയ, ഒരു സ്വതന്ത്ര വിജ്ഞാനകോശം.
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Geometry of the water molecule

തന്മാത്രകളിൽ ആറ്റങ്ങൾ വിന്യസിച്ചിരിക്കുന്നതിന്റെ ത്രിമാനരീതിയെയാണ് തന്മാത്രാ ജ്യോമെട്രി ('Molecular geometry) എന്നതുകൊണ്ട് വിവക്ഷിക്കുന്നത്. ഇതിൽ തന്മാത്രയുടെ രൂപത്തിനുപുറമേ ആറ്റങ്ങൾ തമ്മിലുള്ള ബന്ധത്തിന്റെ നീളം, ബന്ധത്തിന്റെ കോണളവ് തുടങ്ങി ഓരോ ആറ്റത്തിന്റെയും സ്ഥാനം നിർവ്വചിക്കാൻ ഉതകുന്ന അളവുകൾ ഉൾപ്പെട്ടിരിക്കും.

തന്മാത്രാ ജ്യോമെട്രിയുടെ രീതി അനുസരിച്ചാവും പദാർത്ഥങ്ങളുടെ പ്രതിപ്രവർത്തനരീതി, പൊളാരിറ്റി, പദാർത്ഥത്തിന്റെ അവസ്ഥ, നിറം, കാന്തികത, ജീവശാസ്ത്രപരമായ പ്രവർത്തനം എന്നിവയെല്ലാം ഉണ്ടാവുന്നത്.[1][2][3] The angles between bonds that an atom forms depend only weakly on the rest of molecule, i.e. they can be understood as approximately local and hence transferable properties.

വിവിധങ്ങളായ തന്മാത്രാഘടനകൾ[തിരുത്തുക]

A bond angle is the geometric angle between two adjacent bonds. Some common shapes of simple molecules include:

  • Linear: In a linear model, atoms are connected in a straight line. The bond angles are set at 180°. For example, carbon dioxide and nitric oxide have a linear molecular shape.
  • Trigonal planar: Molecules with the trigonal planar shape are somewhat triangular and in one plane (flat). Consequently, the bond angles are set at 120°. For example, boron trifluoride.
  • Bent: Bent or angular molecules have a non-linear shape. For example, water (H2O), which has an angle of about 105°. A water molecule has two pairs of bonded electrons and two unshared lone pairs.
  • Tetrahedral: Tetra- signifies four, and -hedral relates to a face of a solid, so "tetrahedral" literally means "having four faces". This shape is found when there are four bonds all on one central atom, with no extra unshared electron pairs. In accordance with the VSEPR (valence-shell electron pair repulsion theory), the bond angles between the electron bonds are arccos(−1/3) = 109.47°. For example, methane (CH4) is a tetrahedral molecule.
  • Octahedral: Octa- signifies eight, and -hedral relates to a face of a solid, so "octahedral" means "having eight faces". The bond angle is 90 degrees. For example, sulfur hexafluoride (SF6) is an octahedral molecule.
  • Trigonal pyramidal: A trigonal pyramidal molecule has a pyramid-like shape with a triangular base. Unlike the linear and trigonal planar shapes but similar to the tetrahedral orientation, pyramidal shapes require three dimensions in order to fully separate the electrons. Here, there are only three pairs of bonded electrons, leaving one unshared lone pair. Lone pair – bond pair repulsions change the bond angle from the tetrahedral angle to a slightly lower value.[4] For example, ammonia (NH3).

VSEPR table[തിരുത്തുക]

പ്രധാന ലേഖനം: VSEPR theory #AXE method

The bond angles in the table below are ideal angles from the simple VSEPR theory, followed by the actual angle for the example given in the following column where this differs. For many cases, such as trigonal pyramidal and bent, the actual angle for the example differs from the ideal angle, and examples differ by different amounts. For example, the angle in H2S (92°) differs from the tetrahedral angle by much more than the angle for H2O (104.48°) does.

Atoms bonded to
central atom
Lone pairs Electron domains
(Steric number)
Shape Ideal bond angle
(example's bond angle)
Example Image
2
0
2
linear
180°
CO2
Linear-3D-balls.png
3
0
3
trigonal planar
120°
BF3
Trigonal-3D-balls.png
2
1
3
bent
120° (119°)
SO2
Bent-3D-balls.png
4
0
4
tetrahedral
109.5°
CH4
AX4E0-3D-balls.png
3
1
4
trigonal pyramidal
109.5 (107.8°)
NH3
Pyramidal-3D-balls.png
2
2
4
bent
109.5° (104.48°)[5][6]
H2O
Bent-3D-balls.png
5
0
5
trigonal bipyramidal
90°, 120°, 180°
PCl5
Trigonal-bipyramidal-3D-balls.png
4
1
5
seesaw
ax–ax 180° (173.1°),
eq–eq 120° (101.6°),
ax–eq 90°
SF4
Seesaw-3D-balls.png
3
2
5
T-shaped
90° (87.5°), 180° (175°)
ClF3
T-shaped-3D-balls.png
2
3
5
linear
180°
XeF2
Linear-3D-balls.png
6
0
6
octahedral
90°, 180°
SF6
AX6E0-3D-balls.png
5
1
6
square pyramidal
90° (84.8°)
BrF5
Square-pyramidal-3D-balls.png
4
2
6
square planar
90°, 180°
XeF4
Square-planar-3D-balls.png
7
0
7
pentagonal bipyramidal
90°, 72°, 180°
IF7
Pentagonal-bipyramidal-3D-balls.png
6
1
7
pentagonal pyramidal
72°, 90°, 144°
XeOF5
Pentagonal-pyramidal-3D-balls.png
5
2
7
planar pentagonal
72°, 144°
XeF5
Pentagonal-planar-3D-balls.png
8
0
8
square antiprismatic
XeF82−
Square-antiprismatic-3D-balls.png
9
0
9
tricapped trigonal prismatic
ReH92−
AX9E0-3D-balls.png

ത്രിമാന പ്രതിപാദനം[തിരുത്തുക]

  • Line or stick – atomic nuclei are not represented, just the bonds as sticks or lines. As in 2D molecular structures of this type, atoms are implied at each vertex.
Formic-acid-3D-stick.png
L-aspartic-acid-3D-sticks.png
ATP-xtal-3D-sticks.png
Endohedral fullerene.png
NorbornylCation ElectronDensity.jpg
WinsteinYellow.jpg
  • Ball and stick – atomic nuclei are represented by spheres (balls) and the bonds as sticks.
Methanol-3D-balls.png
Methanol struktur.png
PropyleneGlycol-stickAndBall.png
3LRI SolutionStructureAndBackboneDynamicsOfHumanLong arg3 insulin-Like Growth Factor 1 02.png
Methanol.pdb.png
Ubiquitin spheres.png
P-cresol-spaceFilling.png
3GF1 Insulin-Like Growth Factor Nmr 10 01.png
  • Cartoon – a representation used for proteins where loops, beta sheets, alpha helices are represented diagrammatically and no atoms or bonds are represented explicitly just the protein backbone as a smooth pipe.
Beta-meander1.png
MreB.png
Anthrax toxin protein key motif.svg
8tim TIM barrel.png

The greater the amount of lone pairs contained in a molecule the smaller the angles between the atoms of that molecule. The VSEPR theory predicts that lone pairs repel each other, thus pushing the different atoms away from them. ഇവയും കാണുക==

അവലംബം[തിരുത്തുക]

  1. McMurry, John E. (1992), Organic Chemistry (3rd ed.), Belmont: Wadsworth, ISBN 0-534-16218-5 
  2. Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5 
  3. Alexandros Chremos; Jack F. Douglas (2015). "When does a branched polymer become a particle?". J. Chem. Phys. 143: 111104. Bibcode:2015JChPh.143k1104C. doi:10.1063/1.4931483. 
  4. Miessler G.L. and Tarr D.A. Inorganic Chemistry (2nd ed., Prentice-Hall 1999), pp.57-58
  5. Hoy, AR; Bunker, PR (1979). "A precise solution of the rotation bending Schrödinger equation for a triatomic molecule with application to the water molecule". Journal of Molecular Spectroscopy. 74: 1–8. Bibcode:1979JMoSp..74....1H. doi:10.1016/0022-2852(79)90019-5. 
  6. "Archived copy". Archived from the original on 2014-09-03. Retrieved 2014-08-27. 

പുറത്തേക്കുള്ള കണ്ണികൾ[തിരുത്തുക]


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