Drill: Ionic bonding Objective: Swbat: Demonstrate sharing of electrons in order to model covalent bonding by combining Lewis dot diagrams.  

SAT ENRICHMENT: The bonds in BaO are best described as…. Covalent, because valence electrons are shared. Covalent, because valence electrons are transferred. Ionic, because valence electrons are shared. Ionic, because valence electrons are transferred. Metallic, because valence electrons exist in a “mobile sea”.

ENGAGEMENT: Safari Montage Video: Properties of Compounds: Covalent Bonding: http://10.4.1.240/?p=d9e9fc51-8f49-11df-8b67-002219bf32de

Covalent Bonding WebQuest! Covalent Bonding Webquest (SR.CHEMBOND.02A) http://www.visionlearning.com/library/module_viewer.php?mid=55&mcid=&l= 30 min

Covalent Compounds Covalent Bonds Two nonmetals Weaker than ionic bonds Electrons shared, not transferred

Covalent Compounds → Cl + F Cl F → S + O S O Example: Chlorine and fluorine (ClF) Problem 1: Sulfur and oxygen (SO) • • • • ◙ ◙ ◙ ◙ • • → • • Cl + F ◙ Cl F ◙ • • ◙ ◙ ◙ ◙ • • • • ◙ ◙ ◙ ◙ • • • • ◙ • • → • • S + O ◙ S ◙ O ◙ • • • ◙ ◙ ◙ ◙ • ◙ ◙ ◙ ◙

Covalent Compounds → Br + Se + Br Se Br Br → C + O C O Problem 2: Selenium and bromine (SeBr2) Problem 3: Carbon and oxygen (CO) • • • • • • • ◙ ◙ • ◙ ◙ → • Br + ◙ Se ◙ + Br ◙ Se ◙ Br • • • • • • ◙ ◙ • • ◙ • • • • • ◙ • • Br • • • • • ◙ ◙ → • • C + ◙ O ◙ C ◙ ◙ O ◙ • • • • ◙ ◙ ◙ ◙ • ◙

Bond Polarity If there is an unequal sharing of electrons, the bonding electrons spend more time near the atom with the highest electronegativity causing it to obtain a slightly negative charge. The atom with the lower electronegativity acquires a slightly positive charge.

Electronegativities Electronegativities for the first six periods The difference between two elements’ electronegativities indicates the degree of electron sharing (or transfer) in a chemical bond The closer the electronegativity, the more equally the electrons are shared. H 2.1   Li 1.0 Be 1.5 B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Na 0.9 Mg 1.2 Al Si 1.8 P S Cl K 0.8 Ca Sc 1.3 Ti V 1.6 Cr Mn Fe Co 1.9 Ni Cu Zn Ga Ge As Se 2.4 Br 2.8 Rb Sr Y Zr 1.4 Nb Mo Tc Ru 2.2 Rh Pd Ag Cd 1.7 In Sn Sb Te I Cs 0.7 Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At

Nonpolar Covalent Bond- Polar Covalent Bond Polar or Nonpolar? Nonpolar Covalent Bond- Electronegativity difference ≤ 0.4 Polar Covalent Bond 0.4 < Electronegativity difference < 1.7

Predicting Bond Type Example 1: OF2 EN of O = 3.5 EN of F = 4.0 4.0 – 3.5 = 0.5 0.5 is less than 1.7 but greater than 0.4, so the bond is polar covalent.

Example 2: Cl2 Predicting Bond Type EN of Cl = 3.0 3.0 – 3.0 = 0.0 0 ≤ 0.4, so the bond is nonpolar covalent.

Example 3: CS2 C: 2.5 S: 2.5 2.5 – 2.5 = 0.0 Nonpolar Covalent Predicting Bond Type Example 3: CS2 C: 2.5 S: 2.5 2.5 – 2.5 = 0.0 Nonpolar Covalent

Example 4: NH3 N: 3.0 H: 2.1 3.0 – 2.1 = 0.9 Polar Covalent Predicting Bond Type Example 4: NH3 N: 3.0 H: 2.1 3.0 – 2.1 = 0.9 Polar Covalent

Special Case: Polar Covalent Polar covalent molecules have a dipole Molecules with dipoles have partially charged ends For water: Oxygen has an electronegativity of 3.5 Hydrogen has an electronegativity of 2.1 Because oxygen is more electronegative, it will be the negative end of the dipole Because hydrogen is less electronegative, it will be the positive end of the dipole ◙ ◙ ◙ O ◙ H • Negative ◙ • ◙ H Positive

Bonding Complete bonding worksheet 10 min

Summary: Did we accomplish the objective? Explain. Define a Covalent bond. What criteria would you use to assess whether a bond is ionic or covalent? What criteria would you use to assess whether a bond is polar or nonpolar?

Homework: Chromatography Pre-Lab (NO HOMEWORK PASSES MAY BE USED)

Drill: Quiz: Covalent Bonding (5 min) Objective: Swbat: Demonstrate sharing of electrons in order to model covalent bonding by combining Lewis dot diagrams.

SAT ENRICHMENT: Generally… valence electrons are needed for atoms to be most stable. 2 6 8 18 32

Chromatography Lab Review Lab procedures. Chromatography Lab 45 min

Exit Ticket & Extension Covalent Bonding Exit ticket Extension: Oil and Soap Molecule Simulation: http://intro.bio.umb.edu/111-112/111F98Lect/soapandoil.html 5 min

Summary Did we accomplish the objective? Explain. Identify the purpose of the chromatography lab. Explain your chromatography lab results. Which colors were soluble in water?

Homework Instructional Fair Pages 38 and 39!