Chemical Bonding ISCI 2002

Types of Chemical Bonds Valence electrons react Transfer of Electrons forms ionic bonds in compounds Sharing of Electrons forms covalent bonds

Formation of Ionic Bonds and Compounds Metals lose electrons to non- metals Non-metals: stronger electronegativity Metals form “cations” that are positively charged Non-metals form “anions” that are negatively charged

Ion Formation Na = 11 – (11+) and (11-) – Protons and Electrons – When the one electron is lost (11+) + (10-) = +1 Cl = 17 – What will the charge be on chlorine? Electrostatic Attraction between ions forms the bond

Characteristics of Ionic Bonds 1.Very strong; Forms crystalline solids with repeating patterns 2. High Melting and Boiling Points 3.Electrolytes – Conducts electricity in liquid state – Soluble in water 4.Forms Salts – NaCl; MgCl

Covalent Bonding and Compounds Non-metals with similar electronegativities share electrons Molecules are formed – Smallest units of covalent compounds “Molecular Compounds”

Characteristics of Molecular Compounds 1. Liquid or gas at room temperature (may also be solid) 2. Non-electrolytes 3. Boiling points are low; melting point low (if solid)

Polar and Nonpolar Compounds Non-Polar Compounds – Equal sharing Polar Compounds – Unequal sharing – Slight charges on atoms How do you know if a compound is polar or nonpolar? – Differences in Electronegativaties – Shape

Electronegativities If the electronegativities are equal (i.e. if the electronegativity difference is 0), the bond is non-polar covalent If the difference in electronegativities between the two atoms is greater than 0, but less than 2.0, the bond is polar covalent If the difference in electronegativities between the two atoms is 2.0, or greater, the bond is ionic

Bond Prediction Based on Molecular Shape Bent or unsymmetrical geometry – Polar Symmetrical arrangement – Nonpolar

Metallic Bonding Metal electrons “sea of electrons” Interaction of metal nuclei with the electrons that surround them Properties – Conducts electricity and heat – High melting and boiling points – Strong, malleable and ductile – Metallic and opaque (reflect light)

Chemical Changes and Chemical Reactions ISCI 2001

Introduction What is a chemical change? – New substance formed; different properties from the reactants How do we know a chemical reaction has taken place? – (1). Formation of a gas – (2). Permanent color change – (3). Temperature change Exothermic and endothermic – (4). Precipitant formed

Examples Exothermic Reaction – Heat given off during a chemical reaction Endothermic Reaction – Heat absorbed during a chemical reaction Precipitant – Insoluble substance formed during a chemical reaction

Chemical Reactions

Types of Chemical Reactions 1. Synthesis – What does it mean to synthesize something? – A + B  C – Energy input New compound ‘stored energy’ 2. Decomposition – Decomposing! Energy Output – C  A + B – Energy is released

Types of Chemical Reactions 3. Single Replacement – Metal ‘replaces’ another metal in a reaction – One metal is more active! – A + BC  AC + B (A and B are the metals) 4. Double Replacement – “Ion Exchange” – AB + CD  AD + CB (Which are the metals?)