BackChapter 6 Study Guide: Ionic and Molecular Compounds
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Chapter 6: Ionic and Molecular Compounds
Lewis Structures
Lewis structures are diagrams that represent the arrangement of valence electrons in molecules and ions. They help visualize how atoms share or transfer electrons to achieve stable electron configurations.
Key Point 1: Each atom is represented by its chemical symbol, and valence electrons are shown as dots.
Key Point 2: Shared pairs of electrons (covalent bonds) are shown as lines between atoms.
Example: The Lewis structure for water (H2O) shows two hydrogen atoms bonded to an oxygen atom, with two lone pairs on oxygen.
Electronegativity and Polar Bonds
Electronegativity is the ability of an atom to attract shared electrons in a chemical bond. Differences in electronegativity between atoms lead to polar bonds, where electrons are unequally shared.
Key Point 1: The greater the difference in electronegativity, the more polar the bond.
Key Point 2: Polar bonds have a partial positive and partial negative end.
Example: In HCl, chlorine is more electronegative than hydrogen, making the bond polar.
VSEPR Theory
The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the shape of molecules based on the repulsion between electron pairs around a central atom.
Key Point 1: Electron pairs (bonding and lone pairs) arrange themselves to minimize repulsion.
Key Point 2: Common shapes include linear, bent, trigonal planar, tetrahedral, and trigonal bipyramidal.
Example: Methane (CH4) has a tetrahedral shape.
Molecular Shapes
Molecular shape is determined by the arrangement of atoms and electron pairs as predicted by VSEPR theory. Shape affects physical and chemical properties.
Key Point 1: Shapes are named based on the number of bonding pairs and lone pairs on the central atom.
Key Point 2: Examples include linear (CO2), bent (H2O), and trigonal planar (BF3).
Polarity of Molecules
The polarity of a molecule depends on both the polarity of its bonds and its shape. A molecule is polar if it has an uneven distribution of charge.
Key Point 1: Symmetrical molecules with polar bonds may be nonpolar overall.
Key Point 2: Asymmetrical molecules are usually polar.
Example: Water is polar due to its bent shape and polar O-H bonds.
Intermolecular Forces Based on Bond Polarity
Intermolecular forces are attractions between molecules, influenced by bond polarity. These forces affect boiling and melting points, solubility, and other properties.
Key Point 1: Types include dipole-dipole interactions, hydrogen bonding, and London dispersion forces.
Key Point 2: Hydrogen bonds are especially strong and occur in molecules with N-H, O-H, or F-H bonds.
Example: Water molecules are held together by hydrogen bonds, giving water a high boiling point.
