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Chemistry Name(s)
MOLECULAR STRUCTURE; LEWIS STRUCTURES AND
3-D MODELS
INTRODUCTION:
Chemists are often concerned with molecular (^) structure. It is helpful and useful to have a good understanding of the relationship (^) between the two- dimensional, flat molecular structures seen in texts (^) and the better perspective or three-dimensional picture of real molecules. (^) A good way to achieve this understanding or translation (^) from 2-D to 3-D is (^) the use of molecular models, though these are still far from giving the “true” picture (^) of real molecules. As the textbooks frequently show, Lewis structures (^) can be drawn if the molecular formula is given and certain (^) rules for number and (^) placement of electrons are followed. From the Lewis structure (^) for a molecule, (^) a 3-D model can be constructed to give a better (though not perfect) (^) picture of the real molecule.
In this “experiment” the formula of a molecule or (^) molecular ion will be given. An acceptable Lewis structure will (^) be drawn (^) based on that formula. A 3-D model of that molecule or molecular ion will then be constructed using a molecular model kit. An exact 3-D or perspective drawing (^) based on the 3-D model will then be made.
Before performing the “experiment” review the material (^) in the textbook on Lewis structures, VSEPR, bond lengths, and single (^) and multiple (^) bonds.
SUPPLEMENTARY INFORMATION
A. Review the rules for drawing Lewis structures based (^) on the given formula.
- Determine the total number of valence electrons (^) in the formula.
- Apply the octet rule if possible (except (^) for H) to each atom. Keep in mind that there are exceptions to the octet rule.
- If too few electrons are available, multiple (^) bonding may be necessary and if that is the case, resonance may (^) also be possible.
B. The valence shell Iectron (^) Eair .epulsion Theory (^) (VSEPR) is used to determine the geometry of (^) the regions of electron (^) density (electrons pairs or
an effective region where two or more electrons pairs are).
C. Drawing 3-D
Drawing 3-D orperspective structures ofmolecules withtetrahedral, trigonal bipyramidal oroctahedral geometries issomewhat difficult, but (^) possible. Twoexamples (^) ofthetechniques are shown forthemethane molecule,CH 4.
Theatoms are represented by circles. Thesubscripts are (^) for identification only. Placeas manyatomsaspossible in thesame planeasthe central (^) atom. In modelsAand B, H 1 , C, andH 2 are in thesame plane. ModelAshows the line representing the (^) bond just touching the circle ofeach atom. H 3 is in front of the plane of thepaper and is shown (^) by the line connecting it into the circle around (^) C.
H 4 is behind the plane ofthe paper and is shown by the line intothe circle aroundH 4 and just touching (^) the circle (^) around C.
Model Bshows perspective by usingwedge shaped bonds to show positions ofatoms in front (^) or behind (^) the plane ofthe paper. This isbased (^) on the idea that the closer objects are larger. (^) Thismeans that the end ofthe bond closer to the observer is larger than the end farthest from the observer. The diagram below shows end (^) “a” to be closer tothe observer than end ‘b”.
Laboratory Report Sheet Name(s) Chemistry
MOLECULAR STRUCTURE; LEWIS STRUCTURES AND
3-D MODELS
- Molecular Formula Total Valence Electrons
Molecular Geometry of Lewis Structure Central Atom(s)
3-D Drawing
- Molecular Formula Total Valence Electrons
Molecular Geometry of Lewis Structure Central Atom(s)
3-D Drawing
- Molecular Formula (^) Total Valence Electrons
Molecular Geometry of Lewis Structure (^) Central Atom(s)
3-D Drawing
- Molecular (^) Formula Total Valence Electrons
Molecular Geometry of Lewis Structure (^) Central Atom(s)
3-D Drawing
- Molecular Formula Total Valence Electrons
Molecular Geometry of Lewis Structure Central Atom(s)
3-D Drawing
- Molecular Formula Total Valence Electrons
Molecular Geometry of Lewis Structure Central Atom(s)
3-D Drawing
- Molecular Formula Total Valence Electrons
Molecular Geometry of Lewis Structure Central Atom(s)
3-D Drawing
- Molecular Formula Total Valence Electrons
Molecular Geometry of Lewis Structure Central Atom(s)
3-D Drawing
