Introduction to Bonding 2018.notebook February 28, 2018 What is a chemical bond? Unit 9: Chemical Bonding A chemical bond is a sharing or transfer of valence electrons from one atom to another Aim: Why do atoms bond? What kinds of bonds can they form? Dec 1­4:53 PM Dec 1­4:59 PM Why do elements bond? Bond Stability Atoms bond to become more stable. Determine which compound formed will be the most stable. Explain. Two ways that bonding results in a more stable atom: a. C (s) + O2 (g) ‐‐> CO2 (g) + 394 kJ b. 4 Al (s) + 3 O (g) ‐‐> 2 Al O + 3351 kJ 2 Na + Cl2 2 NaCl + 408,854 kJ 2 2 3 forming sodium chloride 2‐8 2‐8‐8 c. 2 H2 (g) + O2 (g) ‐‐> 2 H2O + 484 kJ • Form a stable electron • Forming a bond releases energy configuration (stable octet) • Lower energy= more stability • The more energy released during bond formation, the more stable the bond. Dec 1­5:12 PM Dec 1­5:12 PM 1 Introduction to Bonding 2018.notebook February 28, 2018 IONIC BONDS • The difference in EN is so great METALLIC BONDS that the valence electrons are forced to fully transfer from the • A metallic bond forms between atoms of metal to the nonmetal atom. the SAME metal. • A bond results from the • attraction between the There is an attraction between the oppositely charged ions. loosely held valence electrons and all of the metal atoms' nuclei which causes • Ionic bonds have an E.N. difference the e‐ to become mobile. of 1.7 or greater and the compounds • A metallic bond contains a “sea of mobile formed are called “salts”. electrons”, making them excellent • Salts have a crystal lattice structure and are brittle. conductors in all phases. metal conduction • Ionic compounds will conduct only when in aqueous solution or molten to yield mobile ions. They will not conduct as solids. (To conduct electricity you must have moving charged particles.) salt dissociation • Ionic bonding also occurs in compounds that contain a polyatomic ion Dec 1­5:12 PM Dec 1­5:12 PM Covalent bond: two nonmetal atoms have an EN difference small enough that valence electrons are shared to achieve a stable octet. How many electrons are shared in each of these bonds? Rank each covalent bond type from weakest to strongest. SINGLE COVALENT DOUBLE COVALENT TRIPLE COVALENT BOND BOND BOND NONPOLAR COVALENT BOND POLAR COVALENT BOND Nonpolar covalent bonds Polar covalent bonds occur occur between two identical between two different nonmetal atoms with equal nonmetal atoms with electronegativity resulting in unequal electronegativities NO POLARITY. resulting in POLARITY. H H Cl H Covalent substances are poor conductors because they do not contain charged particles that can become mobile. Dec 1­5:41 PM Dec 1­5:43 PM 2 Introduction to Bonding 2018.notebook February 28, 2018 Coordinate covalent bond: both bonding electrons come from Strength of Bonds the same atom, the other atom involved in the bond contributes no electrons. An atom MUST have an unshared (lone) pair of electrons to form a coordinate covalent bond. Certain polyatomic ions formed from a coordinate covalent + + bond. ex: NH4 and H3O Dec 1­5:41 PM Dec 2­8:17 AM Drawing Lewis Diagrams for Ionic Compounds 1. Always show the correct ratio of cations to anions to show a conservation of charge. # of electrons lost= # of electrons gained Sodium oxide 2e‐ lost= 2e‐ gained Na+ Na+ O2‐ CL Formula: Na2O F Lewis Diagram: Na + O 2‐ Na + 2. The cation's symbol will have an 3. The anion will have a full empty outermost shell (the next outermost shell and a full octet of shell in acts as the valence shell) electrons drawn around it. You and no electrons drawn around it. must indicate the ion charge and You must indicate the ion charge draw brackets. and draw brackets. Dec 2­8:17 AM Nov 28­8:21 AM 3 Introduction to Bonding 2018.notebook February 28, 2018 H O O H H Nov 28­8:21 AM 4.