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Electronegativity and Chemical Bonding

To see how polar, nonpolar, or ionic a compound is, you have to look at the electronegativity difference.

Electroneg Difference Type of Bond0.0 ­ 0.3 Covalent (nonpolar) ­ 2 nonmetals0.31 ­ 1.6 Covalent (polar)> 1.61 Ionic (Metal & Nonmetal)

How to Draw a Lewis Structure: dots and dashes around the element symbol(s) (nuclei) to show the bonding pattern.

Step 1: Determine type and number of atoms in the moleculeStep 2: Draw electron dot structures for each type of atomStep 3: Determine total # of valence electrons combinedStep 4: Arrange atoms to form a skeleton structure

(Usually the least electronegative atom goes in the middle) [Connect the dots!!]

Step 5: Count all electrons and make sure they equal the right amount of valence electrons.

http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_08&folder=bonding

http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_08&folder=lewis_structures

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Example A: Hydrogen Sulfide

Step 1:

Step 2:

Step 3:

Step 4:

Step 5:

Example B: Ammonia

Step 1:

Step 2:

Step 3:

Step 4:

Step 5:

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Polar vs. NonpolarUnequal Dstn of charge = dstn of charge

United atoms have an unequal Bonding electrons are attraction for the shared electron shared equally by the bonded atoms

Happens when there is a bondbetween significantly electroneg. different atomsMolecular Shape

VSEPR Model

­Shape of molecule matters determines if other molecules will react with it

­Model is based on minimizing repulsions of shared and unshared pairs of electrons around the central atom.

­Shared electron pairs repel one another

­Lone pairs determine shape; have a slightly larger orbital than shared electrons.

­Shared bonding orbitals are pushed together slightly by lone pairs.

Covalent Bonding

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WaterLewis Structure:

VSEPR Structure:

VSEPR Shapes

Bent

Pyramidal

Tetrahedral

Planar

Linear

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Odds and Ends.........

­ Electron Affinity­ similar to electronegativity

­ You can have a polar bond but not necessarily a polar molecule.

­ If there is a nonpolar bond (based on electronegativities), then it is a nonpolar molecule Symmetrical (mirror image) = Nonpolar molecule If there is a polar bond

No symmetry = Polar Molecule

­ Remember that like dissolves like. If you have a grease stain on your shirt and you throw it in the wash, will Tide (regular detergent) get the stain out??? Why or why not????

­ Polar molecules and ionic compounds are usually soluble in polar substances

­ Van der Waals forces (Intermolecular Forces)= weak forces of attraction between individual molecules

­ Many physical properties of covalent molecular solids are due to this (ex: melting & boiling points)

­ Bond length decreases with each addition of a multiple bond.

­ The shorter the bond, the stronger it is.

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Resonance

http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_08&folder=resonance

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http://www.ucalgary.ca/~ntaucoin/VSEPRtable.pdf

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VSEPR Problems

http://bertrand.home.mindspring.com/chem/vsframe.htm

http://www.chem.purdue.edu/gchelp/vsepr/contents.html

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