Chapter 6B: Chemical Bonding Cartoon courtesy of NearingZero.net

Essential Question How do electrons behave during ionic bonding? Standard 2a Atoms exchange electrons to form an ionic bond.

6-3 Ionic Bonding and Compounds Ionic Compound- composed of + and - ions combined so charges are equal. (Metal + nonmetal) Formula Unit- simplest group of atoms form an ionic compound.

Cation Formation Main group metals lose all their valence e-’s to form cations (+): This loss of electrons is called oxidation. Na . Na1+ + 1e- sodium Mg: Mg2+ + 2 e- magnesium : Al . Al 3+ + 3 e- aluminum

Anion Formation Non-metals gain e-’s to form anions (-). This process is called reduction. Cl 1- chloride (gain 1 e-) O 2- oxide (gain 2 e-’s) N 3- nitride (gain 3 e-’s)

Ionic Bond - charges are attracted to + charges. - anions are attracted to + cations. The result is an ionic bond. 3-D crystal lattice of anions & cations formed.

Structure of NaCl

Properties of Ionic Compounds Crystals form. High melting point & boiling point. Brittle (breaks easily). Melt when heated (very high temps!) Aqueous solutions conduct electricity. (solutions mixed in water)

Electronegativity (EN) Atoms to the right & top of Periodic Table have greater EN values. F most EN of elements (EN = 4.0). Fr least EN of elements (EN = O.7). Cl =3.0 H = 2.1 S = 2.5 O = 3.5 Na = 0.9 Br = 2.8 C = 2.5 N = 3.0 I = 2.5

Polar & Nonpolar Bonds H-H is non-polar because H & H have the same EN’s. (EN diff. = 0) Cl-Cl is non-polar because Cl & Cl have the same EN’s. (EN diff. = 0) H-Cl is polar because H & Cl have different EN’s. ( H = 2.1, Cl = 3.0 )

Predicting Bond Type There is a continuum between non-polar covalent bonds to ionic bonds. Non-polar bond; little difference in EN between atoms. (EN diff. = 0 – 0.3) Ionic bonds; greatest EN diff between atoms. (EN > 1.7) Polar covalent bonds; in between EN diff between atoms. (EN diff. = 0.3 – 1.7)

Ionic vs. Covalent Bonds Sharing e-’s non-metal + non-metal Molecular (low mp/bp) ex: CO2, Cl2 Macromolecular (high mp/bp) Ex: C(diamond), SiO2 Non conductors Ionic Bonds Exchange e-’s Metal + non-metal 3-D units (crystals) high mp/bp Brittle, melt Ex: NaCl conduct electricity

Ionic Bonding in NaCl

Ionic Bonding in NaCl

6-4 Metallic Bonding Metals- conduct heat, have low ionization energy Low EN; give up electrons easily. Metals have luster (shine), are malleable (can be hammered into sheets) and are ductile (drawn into wires).

Metallic Bonding Metallic Bonding - type of bonding found in metallic crystals. 3-D lattice of positive ions. remain fixed in a crystal lattice. loosely-held valence e-’s move freely throughout the crystal. The fluid-like movements of valence e-’s make metals good conductors of heat and electricity.

Metallic Bonding

Metal Alloys Alloys -metallic substances composed of two or more elements; at least one of these elements is a metal. Alloys are important because the properties of an alloy are often superior to those of its component elements.

Common Metal Alloys Stainless steel (composed of Fe, Cr, C, Ni) Sterling silver  (composed of Ag & Cu) 14 karat gold (composed of Au & Cu) Note:  Pure gold too soft for jewelry!) Brass/bronze  (composed of Cu & Zn)

6-5 Molecular Geometry E- pairs around the central atom stay as far apart as possible. Consider non-bonding (lone pairs) as well as bonding e-’s. E- pairs in single, double and triple bonds are treated as single e- clouds.

VSEPR Theory Valence Shell Electron Pair Repulsion Theory (VSEPR) Two e- clouds around a central atom form a linear shape as in CO2 and BeF2 Three e- clouds form a trigonal planar shape as in BF3

VSEPR Theory The shape formed by the four e- pairs is called a tetrahedron as in CH4. In water, H2O, two of the corners are occupied by hydrogens. Gives water molecule its bent shape.

Structure of H2O .. : Bonded e- pairs are often represented as lines: So H2O would look like this: There are a total of 2 e- pairs which try to get as far away from each other as possible. Result = bent shape. .. : O H H

Bent Shape of H2O

Hydrogen Bonding Hydrogen bonding - strongest of the intermolecular bonds (bonds between molecules). Hydrogen bonding - hydrogen atoms bonded to highly EN elements such as F, O, and N. Hydrogen bonding - responsible for the relatively high MP & BP of water.

Chapter 6B SUTW Prompt Describe the different properties of ionic bonds and metallic bonds by describing how the electrons interact with each bonding type. Complete an 8-12 sentence paragraph using the SUTW paragraph format. Highlight using green, yellow, and pink. Due Date: Tomorrow (start of class).