F. Schifano, Department of Science Bayonne High School Bayonne, NJ 07002 • Five Days of Instruction and Practice • Two Labs: Covalent vs. Ionic and Molecular Modeling (total 5 points) • One Day of In-class Review: 16 March 2011 • Afterschool Session: 16 March 2011 3-5 pm • Full-Unit Test: 17 March 2011 (13.5 points) NJCCCS 5.2.12.B.1. (...chemical bonds are the interactions between atoms that hold them together in molecules or between oppositely charged ions.) Explain how and why chemical bonds form Distinguish between the types of chemical bond Relate bond types to observable chemical properties Indicate the three-dimensional structure of molecules A chemical bond is a relationship between two or more atoms that involves the transfer or sharing of electrons. Chemical reactions are the observable consequences of making and breaking bonds. The formation or breaking of a bond results in a chemical change– an energy change and the production of a new product substance. Enthalpy is the potential energy stored in chemical bonds. Chemical reactions release or absorb heat because the total enthalpy in the reactants is different than the total enthalpy of the products. Mixtures are combinations of atoms that involve only physical jumbling rather than chemical bonding. ◦ Formed and separated by physical changes Intermolecular forces– weak, transient interactions between molecules control some physical, but not chemical properties. ◦ Next unit we will focus on these. Atoms form bonds because in doing so they can rearrange their electrons in a way that makes them more stable. Bonds are a way for atoms to achieve valence = 8. ◦ Hydrogen is stable at VAL=0 or VAL =2 ◦ Boron is stable at VAL = 6 Gilbert Lewis (ENG-1916) invented the structures to show on paper how molecules were bonded. Lines represent covalent bonds. Each line counts as two electrons. Dots represent unshared electrons. Unshared pairs are called lone pairs. Atoms have different needs to achieve stability so they will form different numbers and kinds of bonds. Elements Valence Number of Bonds Number of Lone Pairs Satisfied at this valence: H 1 1 0 1 F, Cl, Br, I 7 1 3 8 O, S, Se 6 2 2 8 N, P 5 3 1 8 C, Si 4 4 0 8 B 3 3 0 6 You should copy this slide to your formula sheet. Write the highest bond order atom in center Link together all other high bond-order elements Resolve all remaining bonds so all VAL are fulfilled Write the highest bond order element in the center. Attach all other high-bond order elements to this central atom by single bonds. Show all missing bonds as empty lines. Use any available 1-bond order elements to fill up empty bonds. If there are any empty bonds on adjacent molecules, use multiple bonds to fill them. Write the Lewis structures of each of the following substances. C H CH4 H3CCl CO2 BF3 HCl NH3 CH2O NH2CH3 H2O H2S CH3CH2OH PCl3 N2 H2C2 C H CH4 H3CCl CO2 BF3 HCl NH3 CH2O NH2CH3 H2 O H2 S CH3CH2OH PCl3 H2 N2 CH2F2