COVALENT COMPOUNDS

• Covalent Compounds • Ionic Compounds • Formed when two • Formed when two elements, usually 2 elements, usually a nonmetals, SHARE metal and a nonmetal, electrons. TRANSFER electrons. Electronegativity • Electronegativity is the ability of an atom to attract a pair of electrons in a chemical bond. • An electronegativity difference greater than 1.7 is usually considered to be a ionic bond. • Less than 1.7 but greater than 0 is POLAR COVALENT. Electrons are shared but not equally. • Equal to zero is NONPOLAR COVALENT. Electrons are EQUALLY SHARED BETWEEN THE 2 ATOMS. • lithium and fluorine • oxygen and chlorine http://www.meta-synthesis.com/webbook/30_timeline/pauling.jpg • nitrogen and nitrogen Lewis Electron Dot Structures • Count the total number of valance electrons for all of the atoms. • Arrange the elements around the central atom. Atom with lowest electronegativity or smallest number of atoms. • Connect all elements to the central atom with a single pair of electrons. • Place lone pair electrons on external atoms until they have an octet. • If there are extra electron they are placed on the central atom; even if that atom has more than on octet. • Use double and triple bonds if you http://www.chem.wisc.edu/~newtrad/CurrRef/BDGTopic/BDGFigs/1_8l ewdot.gif do not have enough electron to give every atom an octet. Lewis Electron Dot Practice

• water (H2O) • sodium chloride (NaCl)

• aluminum oxide (Al2O3) • ammonia (NH3) • methane (CH4) • carbon dioxide (CO2) • phosphorus pentachloride (PCl5) • sulfur hexafluoride (SF6) Molecular Shapes

• The shapes of molecules determine many of their chemical and physical properties. • VSEPR: valance shell electron pair repulsion. • This model minimizes the repulsion of shared and unshared electrons. Polar and Nonpolar

• Molecules are either polar or nonpolar based on the nature of the bonds in the molecule. • Polar molecules are NONSYMETRICAL; one • http://www.800mainstre side of the molecules has et.com/5/0005-009- a slight positive charge samplesshap.gif and one side has a slight negative charge. • Nonpolar molecules are SYMETRICAL; no overall http://www.800mainstreet.com/5/0005-009-samplesshap.gif charge in the molecule. Covalent Molecules

• Date: • Partners: • Problem: How can the Lewis Electron Dot Model and VSEPR be used to determine the shape and polarity of covalent molecules? • Hypothesis: Procedures

• Materials: Molecular Model Kits • black = carbon; red = oxygen; blue = nitrogen; white = hydrogen; green = chlorine; orange = bromine; purple = iodine; gray = phosphorus; yellow = sulfur; • stick = single bond; spring = multiple bond • Procedures: • Assemble the model for each of the molecules listed. • Draw the electron dot diagram for each molecule. • Calculate the electronegativity difference to determine the type of bond. • Determine the shape of the molecule. • Determine the type of molecule. Results Formula and Electron – Dot Electronegativity Shape of Type of Name Diagram Difference Molecule Molecule Calculation (Remember, this is And Bond Type not the same as bond type.)

hydrogen: H2 (diatomic element)

iodine: I2 (diatomic element)

water: H2O

hydrogen bromide: HBr

hydrogen cyanide: HCN

Methane: CH4

carbon dioxide:

CO2

ammonia: NH3

carbon tetrabromide:

CBr4 phosphorus pentachloride: PCl5

sulfur hexaiodide: SI6

Ethane: C2H6 carbon – carbon

carbon - hydrogen Conclusion

• Conclusion: • • Theoretical Discussion: • Research VSEPR. • Questions: • 1. Do all molecules that have polar bonds make polar molecule? Explain by giving examples. • 2. Both water and carbon dioxide are triatomic molecules. Explain why water is polar and carbon dioxide is nonpolar.