Electronegativity (): This is a measure of an atom's ability to attract shared electrons in a chemical bond. It increases across a period due to higher effective nuclear charge and decreases down a group due to increased electron shielding.
Bond Classification: The difference in electronegativity () determines the bond type. A to typically indicates an Ionic Bond, while a indicates a Covalent Bond.
Polarity: Within covalent bonds, if , the bond is Polar Covalent, meaning electrons are shared unequally. If , the bond is Non-polar Covalent, with nearly equal sharing.
Mechanism: Ionic bonds form through the complete transfer of one or more electrons from a metal (low electronegativity) to a non-metal (high electronegativity). This creates oppositely charged ions: cations (+) and anions (-).
Coulombic Force: The bond is the result of the strong electrostatic attraction between these ions. This force is governed by Coulomb's Law: , where represents the charges and the distance between them.
Structure: Unlike covalent compounds, ionic substances do not form discrete molecules. Instead, they arrange themselves into a repeating 3D pattern called a Crystal Lattice, which maximizes attractive forces and minimizes repulsions.
Identify the Elements: The quickest way to predict bond type is checking the periodic table. A metal-nonmetal pair is usually ionic, while a nonmetal-nonmetal pair is covalent.
Check Conductivity: If a question mentions a substance that only conducts electricity when dissolved or melted, it is a hallmark of an ionic compound. Covalent molecular substances do not have mobile ions to carry charge.
Polyatomic Ions: Be careful with compounds like or . These contain both ionic bonds (between the cation and anion) and covalent bonds (within the polyatomic ion itself).
Electronegativity Values: If values are provided, always calculate . Do not rely solely on the metal/non-metal rule, as some combinations (like ) have significant covalent character despite being metal-nonmetal.
