This article reviews key concepts from AP Chemistry Unit 2, focusing on chemical bonds, electronegativity trends, and the factors influencing bond properties and lattice energy.
Electronegativity and Bond Polarity
•Electronegativity generally increases left to right across a period and decreases top to bottom down a group on the periodic table.•In polar covalent bonds, the atom with greater electronegativity carries a partial negative charge (δ−), while the other has a partial positive charge (δ+).•Bond polarity increases with greater electronegativity difference between atoms, which can often be inferred from their positions on the periodic table.•For binary compounds, metals bonded with nonmetals typically form ionic bonds, while two nonmetals form covalent bonds, though exceptions exist along a continuum.Bond Properties and Lattice Energy
•Bond length and bond energy are inversely related; longer bonds (e.g., H–I) are easier to break (lower bond energy) than shorter bonds (e.g., H–F).•Higher bond order (single vs. double vs. triple) decreases bond length and increases bond energy for the same atom pair.•Lattice energy, the energy to separate ions in a solid, depends on Coulomb's law: greater ion charge magnitude and smaller ionic radii increase lattice energy (e.g., MgO > NaF > KCl).•Metallic bonding involves a lattice of positive ions with delocalized valence electrons, enabling electrical conductivity in solids like copper.Key Takeaways
•Electronegativity trends dictate bond polarity and type, with polar bonds having partial charges based on atom positions in the periodic table.•Bond length and energy are inversely related, and bond order affects these properties, with triple bonds being shortest and strongest.•Lattice energy in ionic compounds is influenced by ion charge and size, following Coulomb's law to predict stability and properties.Conclusion
Mastering these principles of chemical bonding and periodic trends is essential for analyzing molecular structures and predicting compound behavior in AP Chemistry.
