lecture recording on 24 January 2025 at 09.11.42 AM

Key Concepts in Ionic Bonds and Chemical Reactions

Water and Chemical Formulas

  • Water is chemically known as Dihydrogen Monoxide (H2O).

  • Other humorous misconceptions about chemical notation were presented, highlighting the complexities and confusions in naming chemical compounds.

Atomic Structure and Octet Rule

  • Atoms aim to achieve a stable electron configuration similar to noble gases. This is often achieved by filling their outermost shell (valence shell).

  • Octet Rule: Atoms generally desire 8 electrons in their valence shell. Exceptions include:

    • Helium (He), Lithium (Li), Beryllium (Be), Boron (B), and Hydrogen (H), which follow the Duet Rule (2 electrons are stable for these).

Example of Fluorine and Chlorine

  • Fluorine (atomic number 9):

    • Protons: 9, Electrons: 9

    • Most stable ion: Fluorine ion (F-) with a charge of minus 1 because it gains 1 electron to fulfill the octet rule.

  • Chlorine behaves similarly to fluorine, also gaining 1 electron for a stable form (Cl-).

  • Elements in Group 17 (Halogens) generally want to gain 1 electron.

Stability of Ions

  • Lithium (Group 1) aims to lose 1 electron to become stable.

  • Charges by group:

    • Group 1: Typically forms +1 cations.

    • Group 2: Typically forms +2 cations.

    • Group 13: Typically loses 3 electrons.

    • Group 17: Gains 1 electron (forms -1 anions).

    • Group 14 can either gain or lose 4 electrons but typically only applies to Carbon.

Naming Cations and Anions

  • Positive ions are called Cations. Example: Calcium ion (Ca²+).

  • Negative ions or anions typically end in "-ide" when simpler or have roots indicating their polyatomic nature, such as SO₄²⁻ for sulfate.

  • Common polyatomic ions include nitrate (NO₃⁻), sulfide (S²-), and chloride (Cl-).

Ionic Bonds Overview

  • Ionic bonds form through the transfer of electrons between atoms, creating charged ions that attract each other.

  • Example: Sodium (Na) can lose an electron to become Na+ and Chlorine (Cl) gains an electron to become Cl-.

    • This creates Sodium Chloride (NaCl)

  • Salts are defined as ionic compounds, not exclusively sodium chloride.

Properties of Ionic Compounds

  • Ionic compounds generally have:

    • High melting and boiling points due to strong electrostatic forces requiring significant energy to break them.

    • Being brittle, meaning they can break under stress rather than deform.

    • Conductivity when dissolved in solution or molten due to the presence of free-moving ions.

Criss-Cross Rule for Ionic Compounds

  • For writing formulas, the criss-cross method can be used:

    • Charges of the ions are swapped to balance the total positive and negative charges.

  • Example: For Aluminum (Al³+) and Oxygen (O²-), the formula becomes Al₂O₃ after applying the criss-cross method.

Transition Metals and Variable Charge

  • Transition metals can exhibit variable charges, often requiring Roman numerals in naming to specify their charge.

  • Example: Iron can be either Fe²+ or Fe³+, hence Iron(II) Oxide for FeO and Iron(III) Oxide for Fe₂O₃.

Summary of Basic Naming Conventions

  • Cation names remain the same (e.g., Sodium = Sodium ion).

  • Cations with variable charges require Roman numerals (e.g., Fe²+ = Iron(II)).

  • Anions are named by modifying the root name and adding "-ide" or using the established names for polyatomic ions.