LEWIS DOT STRUCTURES , MOLECULAR SHAPES, AND ...



LEWIS DOT STRUCTURES and VSEPR MOLECULAR SHAPES

Valence electrons— electrons occupying the last s & p sublevels used. The number of valence electrons is easily determined for Representative elements. You simply need to look at the group number. Examples: Group 1A elements like sodium have 1 valence electron. Group 6A elements like oxygen have 6 valence electrons.

Lewis Structures—a representation of a molecule which reflects atoms present and the number of shared and unshared electrons present.

Lone pair—non bonded electron pair

Bonding electrons—pairs of electrons shared between 2 atoms

ELECTRONIC GEOMETRY—the basic arrangement of atoms about a central atom. It is determined by counting the total number of atoms bound to central atom and adding it to the number of lone pairs on the central atom. This total will be equal to a value 1-6. Those numbers correspond to one of the basis shapes in bold .

MOLECULAR GEOMETRY—the specific geometry of atomic arrangement around a central atom based upon bond atoms and lone pairs.

How to Construct Lewis Dot Structures for Molecules:

1. Determine the type and number of atoms present in the molecule

2. Determine the number of valence electrons each atom will supply (you may wish to draw the electron dot diagram for that atom) If you are asked to do the structure of a polyatomic ion: add to the total number of electrons if the ion is negative; subtract from the total number of electrons if the ion is positive.

Example: if an ion has a –3 charge, add 3 more electrons to the total of valence electrons.

3. Total the number of valence electrons in the atoms to be combined

4. Arrange the atoms to form a skeletal structure for the molecule. The central atom is always the least electronegative atom. (Hydrogen is never the central atom!)

5. Add connect the atoms by adding electron pair bonds.

6. Add unshared electron pairs around the remaining atoms so that everything is satisfied with an octet (note some atoms like hydrogen are satisfied when they have 2 valence electrons).

7. Count to make sure that the number of electrons used equals the number of electrons available.

- if too many electrons are used, take away one or more lone pairs (non-bonded electron pairs) until the correct number of electrons is achieved. Then move 1 (or more) of the lone pairs to a bonding position between a non-hydrogen atom and a central atom to form a double bond.

ELECTRONIC GEOMETRY AND VSEPR MOLECULAR GEOMETRY:

To determine a geometry, first construct a Lewis structure, then consult the table below:

|# of atoms |# of Lone pairs |Electronic Geometry |VSEPR Molecular Geometry |Predicted |Example |Hybridization |

|bonded to |of electrons | | |Bond |Molecule | |

|Central atom | | | |Angles | | |

|2 |0 |Linear |Linear |180˚ |BeCl2 | |

| | | | | | |sp |

|4 |0 |Tetrahedral |Tetrahedral |109.5˚ |CH4 | |

| | | | | | |sp3 |

|2 |2 |Tetrahedral |Bent |104.9 |water |sp3 |

|1 |3 |Tetrahedral |linear | |HF |sp3 |

|5 |0 |Trigonal-bypyramidal |Trigonal-bypyramidal |120˚, |PCl5 |sp3d |

| | | | |90˚ | | |

|3 |2 |Trigonal-bypyramidal |T-shaped | |ClF3 |sp3d |

|2 |3 |Trigonal-bypyramidal |Linear | |XeF2 |sp3d |

|6 |0 |Octahedral |Octahedral |90˚ |SF6 |sp3d2 |

|4 |2 |Octahedral |Square Planar | |XeF4 |sp3d2 |

Pre AP Chemistry Electronic and Molecular Geometry Worksheet HW 2A

To determine molecular geometry, first construct a Lewis structure, then consult the table below:

| |MOLECULE | Total Number|Lewis Dot |Predicted |Is it polar? |Hybridization |Possible |

| | |of Valence |Structure |Molecular shape | | |types of |

| | |Electrons | | | | |I.M.F’s |

| | |Available | | | | | |

|1 |OCl2 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|2 |HF | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|3 |CHCl3 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|4 |H2S | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|5 |CO2 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|6 |CH3OH | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|7 |O2 | | | | | | |

| | | | | | | | |

|8 |ICl3 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| |MOLECULE | Total Number|Lewis |Predicted |Is it |Hybridization |Possible |

| | |of Valence |Structure--- |Molecular shape |polar? | |types of |

| | |Electrons | | | | |I.M.F’s |

| | |Available | | | | | |

|9 |N2 | | | | | | |

| | | | | | | | |

| | | | | | | | |

|10 |(SO3)-2 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|11 |KrF4 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|12 |IF5 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

|13 |COS | | | | | | |

| | | | | | | | |

|14 |CF2Cl2 | | | | | | |

| | | | | | | | |

|15 |*HNO3 | | | | | | |

| | | | | | | | |

| | | | | | | | |

|16 |SeCl6 | | | | | | |

| | | | | | | | |

| | | | | | | | |

| | | | | | | | |

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download