Chemical Bonds (Ionic and Covalent Bonds) Part 1 Textbook Pages: 52-63

Chemical Bonds Chemical Bonds: The forces that attract atoms to each other in compounds. Ionic Bond: The attractive electrostatic force between a negative ion and a positive ion. Covalent Bond: The attraction between atoms that results from the sharing of electrons. A filled valence shell makes atoms stable Therefore, when bonds form between atoms, they do so in a way that gives each atom a filled valance shell (stable octet). Octet Rule: When bonds form between atoms, the atoms gain, lose, or share electrons in a way that they crate a filled outer shell containing eight (8) electrons.

Covalent (Molecular) Compounds Ionic vs. Covalent Property Ionic Compounds Covalent (Molecular) Compounds Types of elements involved Metal and Nonmetal Two Nonmetals What happens to electrons? Electrons Transferred Electrons Shared Type of bond that forms Ionic Covalent State at Room Temperature Solid Solid, Liquid, or Gas Solubility in Water Soluble Insoluble Electrical Conductivity in Solution Conducts Does not conduct

Old Way of Bond Classification BEFORE, classification of bond type was easy. To know us the bond type all we did was look at the types of elements in the compounds. Examples: NaCl (metal + non-metal) IONIC CH4 (nonmetal + non-metal) COVALENT Consider the following compound: BeH2 Be is a metal H is a non-metal You think it’s going to be an ionic compound, BUT it is in fact a COVALENT compound!!! Therefore, our “inspection” method of classifying bond type is no longer sufficient to predict the classification of bond type.

Electronegativity and Bond Classification Electronegativity: A measure of an element’s ability to attract electrons in a chemical bond. By comparing the electronegativity values of two elements involved in a chemical bond, we can determine whether they will: Transfer electrons (IONIC) Share electrons (COVALENT) Unequal sharing of electrons (POLAR COVALENT) Equal sharing of electrons (COVALENT)

Electronegativity and Bond Classification Examples: Classify the type of bond present for each of the following compounds: CH4 B2S3 CaO H2O

Ionic Compounds Ionic compounds transfer electrons to produce positive ions and negative ions. The oppositely charged ions attract each other. The attraction is what holds the ions together. This attraction is strong. It is this attraction that give ionic compounds HIGH melting points and makes them solid at room temperature. Since the ions are charged, when they dissolve in water, they can conduct electricity by facilitating the movement of the ions through the liquid.

Rules for Drawing Lewis Structures for Ionic Compounds 1. Write the ionization equation of each element. Use this to determine the number of electrons transferred by each element. Multiply the equations (if necessary) to equalize the number of electrons lost and gained. 2. Each ion goes in a set of square brackets [ ] with the charge outside the bracket corresponding to the number of electrons lost or gained. 3. Alternate ions of opposite charges.