Ionic Compounds

Introduction to Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between positively charged cations and negatively charged anions. They typically consist of metals and nonmetals and are fundamental to understanding chemical bonding in GOB Chemistry.

• Charge Prediction: The charge of a main group ion can be predicted based on its position in the periodic table. For example, Group 1 elements form +1 ions, Group 2 form +2 ions, Group 17 (halogens) form -1 ions, etc.

• Nature and Formation: Ionic compounds form when atoms transfer electrons to achieve stable electron configurations, usually resulting in a full outer shell.

• Formula Prediction: The formula of an ionic compound is determined by balancing the total positive and negative charges so the compound is electrically neutral.

• Naming Ions:

  • Main group cations and anions: Main group metals form cations (e.g., Na+, Ca2+), while nonmetals form anions (e.g., Cl-, O2-).

  • Transition metal cations: Transition metals can form cations with different charges (e.g., Fe2+, Fe3+).

  • Polyatomic ions: Ions composed of more than one atom, such as SO42- (sulfate) or NH4+ (ammonium).

• Naming Ionic Compounds: The name of an ionic compound includes the cation name followed by the anion name. For transition metals, the charge is indicated in Roman numerals (e.g., iron(III) chloride).

• Writing Formulas: To write the formula from the name, combine the ions in ratios that result in a neutral compound. For example, magnesium chloride: Mg2+ and Cl- combine as MgCl2.

• General Properties: Ionic compounds are typically solid at room temperature, have high melting and boiling points, and conduct electricity when dissolved in water.

Example: Sodium chloride (NaCl) is formed from Na+ and Cl- ions. The charges balance to form a neutral compound.

Covalent Compounds

Introduction to Covalent Compounds

Covalent compounds are formed when two or more nonmetals share electrons to achieve stable electron configurations. These compounds are essential in organic and biological chemistry.

• Nature and Formation: Covalent bonds form when atoms share pairs of electrons. This sharing allows each atom to attain a noble gas configuration.

• Binary Covalent Compounds: Compounds composed of two different nonmetals (e.g., CO2, H2O).

• Lewis Dot Structures: Diagrams that show the arrangement of valence electrons among atoms in a molecule.

• Molecular Shape (VSEPR): The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts the 3D shape of molecules based on electron pair repulsion.

• Electronegativity: A measure of an atom's ability to attract shared electrons. Electronegativity differences determine bond polarity.

• Bond Polarity: If the difference in electronegativity between two atoms is significant, the bond is polar. If not, it is nonpolar.

• Molecular Polarity: Determined by both the shape of the molecule and the polarity of its bonds.

• Intermolecular Forces: Forces between molecules, including:

  • Dipole-dipole: Attraction between polar molecules.

  • Hydrogen bonding: A strong type of dipole-dipole interaction involving H bonded to N, O, or F.

  • London dispersion forces: Weak attractions due to temporary dipoles in all molecules.

  • Induced dipole: Attraction between a polar molecule and a nonpolar molecule.

• Physical Properties: Intermolecular forces affect boiling point, melting point, and solubility. Stronger forces result in higher boiling and melting points.

• Types of Solids: Solids can be classified by the types of forces holding them together: molecular, ionic, covalent network, and metallic solids.

Example: Water (H2O) is a polar covalent molecule with hydrogen bonding, resulting in a high boiling point compared to other molecules of similar size.

Table: Comparison of Ionic and Covalent Compounds

Key Equations and Concepts

• Electronegativity Difference:

• Lewis Structure Electron Count:

• VSEPR Theory: Electron pairs around a central atom arrange themselves to minimize repulsion, determining molecular shape.