Chapter 5: Soap

Section 5.1—Types of Bonds Objectives: distinguish between 4 types of bonding describe the characteristics of each type of bonding

Why atoms bond Atoms are most stable when they’re outer shell of electrons is full Atoms bond to fill this outer shell For most atoms, this means having 8 electrons in their valence shell  The Octet Rule: atoms will gain, lose, or share electrons in order to obtain a full set of 8 valence electrons Common exceptions are Hydrogen and Helium which can only hold 2 electrons.

The Octet Rule & the Formation of Ions Na Cl Sodium has 1 electron in it’s valence shell Chlorine has 7 electrons in it’s valence shell Metals give electrons away to reveal a full level underneath. - Recall from the Octet Rule that atoms will gain, lose... in order to obtain a full set of 8 valence electrons Nonmetals 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

The Octet Rule and Covalent Bonds 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 equally form non-polar covalent bonds Non-metals that share electrons unequally form polar covalent bonds Recall from the Octet Rule that atoms will gain, lose, or share in order to obtain a full set of 8 valence electrons

In a nonpolar covalent bond, electrons spend an equal amount of time with each nucleus. In a polar covalent bond, the electrons spend more time with one nucleus and less time with the other.

Metallic bonding Metal atoms form lattice structures. Each atom contributes their valence electrons to form a “sea of electrons” that are shared by all the metal atoms.

The valence electrons are free to move throughout the structure. The part of each metal atom that remains (the nucleus and inner core electrons) is called a metallic cation. The electron sea belongs to no one metallic cation but 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 points. This is because it’s hard to pull apart those + and – charges. They are strongly attracted to one another.  At room temperature, then, they found as solids! Polar covalent bonds have the next highest melting/boiling points  Most are solids or liquids under normal conditions Non-polar covalent bonds generally 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

Practice Problems 1. Identify the following compounds as ionic or covalent. a. AlCl 3 b. C 6 H 12 O 6 c. NO 2 d. NaOH 2. Which substance(s) above would dissolve in water and conduct electricity? 3. Which substance(s) have lower melting & boiling points? 4. Describe how metallic bonding allows malleability.