Chapter 5: Soap

Introductory Activity Fill a test tube with an inch of water Add a squirt of cooking oil to the test tube. Observe Stopper, shake & observe Add a few drops of soap. Observe With another test tube, add water & soap only. Observe. Compare the two test tubes. Make particle visualizations describing each test tube.

Introductory Activity What ideas do you have about how soap works? What kinds of things do advertising and marketing tell you? What do the soap companies want you to know about how soap works?

Soap This chapter will introduce the chemistry needed to understand how soap works Section 5.1: Types of bonds Section 5.2: Drawing Molecules Section 5.3: Compounds in 3D Section 5.4: Polarity of Molecules Section 5.5: Intermolecular Forces Section 5.6: Intermolecular Forces and Properties

Inter-molecular forces Bonding types & Structures Soap Works based on Inter-molecular forces Determined by Molecular Geometry Determined by Bonding types & Structures

Section 5.1—Types of Bonds

Why atoms bond Atoms are most stable when they’re outer shell of electrons is full Atoms bonds to fill this outer shell For most atoms, this means having 8 electrons in their valence shell Called the Octet Rule Common exceptions are Hydrogen and Helium which can only hold 2 electrons.

One way valence shells become full - - - - - - - - - - - - - Na - Cl - - - - - - - - - - - - - - Sodium has 1 electron in it’s valence shell Chlorine has 7 electrons in it’s valence shell Some atoms give electrons away to reveal a full level underneath. Some atoms gain electrons to fill their current valence shell.

One way valence shells become full - - - + - - - - - - - - - - - Na - Cl - - - - - - - - - - - - - - The sodium now is a cation (positive charge) and the chlorine is now an anion (negative charge). These opposite charges are now attracted, which is an ionic bond.

Ionic Bonding—Metal + Non-metal Metals have fewer valence electrons and much lower ionization energies (energy needed to remove an electron) than non-metals Therefore, metals tend to lose their electrons and non-metals gain electrons Metals become cations (positively charged) Non-metals become anions (negatively charged) The cation & anion are attracted because of their charges—forming an ionic bond

Bonding between non-metals When two non-metals bond, neither one loses or gains electrons much more easily than the other one. Therefore, they share electrons Non-metals that share electrons evenly form non-polar covalent bonds Non-metals that share electrons un-evenly form polar covalent bonds

Metals bonding Metals form a pool of electrons that they share together. The electrons are free to move throughout the structure—like a sea of electrons Atoms aren’t bonded to specific other atoms, but rather to the network as a whole

Bond type affects properties The type of bonding affects the properties of the substance. There are always exceptions to these generalizations (especially for very small or very big molecules), but overall the pattern is correct

Melting/Boiling Points Ionic bonds tend to have very high melting/boiling points as it’s hard to pull apart those electrostatic attractions They’re found as solids under normal conditions Polar covalent bonds have the next highest melting/boiling points Most are solids or liquids under normal conditions Non-polar covalent bonds have lower melting/boiling points Most are found as liquids or gases

Solubility in Water Ionic & polar covalent compounds tend to be soluble in water Non-polar & metallic compounds tend to be insoluble

Conductivity of Electricity In order to conduct electricity, charge must be able to move or flow Metallic bonds have free-moving electrons—they can conduct electricity in solid and liquid state Ionic bonds have free-floating ions when dissolved in water or in liquid form that allow them conduct electricity Covalent bonds never have charges free to move and therefore cannot conduct electricity in any situation