2.3 Chemical Bonding and Molecular Geometry

Chemical bonds are the foundation of molecular structures. Ionic, covalent, and metallic bonds form through electron interactions, influenced by element properties like electronegativity. Understanding these bonds helps predict how atoms combine and behave in various substances.

Molecular structure and geometry determine a compound's shape and properties. The octet rule and Lewis structures visualize electron arrangements, while VSEPR theory predicts 3D shapes. These concepts are crucial for understanding molecular behavior and reactivity in chemical systems.

Chemical Bonding

Types of chemical bonds

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• Ionic bonds form between metals and nonmetals through electron transfer resulting in electrostatic attraction between oppositely charged ions (NaCl)
• Covalent bonds form between nonmetals through electron sharing creating polar and nonpolar subtypes (H2O, CO2)
• Metallic bonds form between metal atoms with delocalized electrons creating a "sea of electrons" model (Cu, Al)

Bond prediction from element properties

• Electronegativity measures atom's ability to attract electrons in a chemical bond determines bond type (Pauling scale)
• Periodic table trends show metal vs. nonmetal locations influencing bond formation (alkali metals form ionic bonds)
• Ionization energy and electron affinity influence bond formation by determining ease of electron loss or gain
• Oxidation states relate to bond type prediction by indicating electron transfer or sharing (Fe2+, Cl-)

Molecular Structure and Geometry

Octet rule and Lewis structures

• Octet rule states atoms tend to have 8 valence electrons exceptions include H and Be
• Lewis structures use electron dot diagrams to represent single, double, and triple bonds (CH4, O2, N2)
• Formal charge calculation determines charge distribution within molecules affects stability
• Resonance structures occur when multiple valid Lewis structures represent delocalized electrons (benzene)
• Expanded octets allow elements like P and S to have more than 8 valence electrons forming hypervalent molecules (PCl5)

Molecular geometry and polarity

• VSEPR theory predicts 3D molecular shapes based on electron domain geometry and molecular geometry
• Common VSEPR shapes include linear, trigonal planar, and tetrahedral lone pairs affect geometry (H2O bent shape)
• Bond angles vary for different geometries ideal tetrahedral angle is 109.5°
• Molecular polarity depends on bond polarity and molecular symmetry creates dipole moments (NH3 polar, CCl4 nonpolar)
• Hybridization explains molecular geometry through $sp$, $sp^2$, and $sp^3$ orbital mixing (CH4 $sp^3$ hybridized)