4.4 Ionic Bonding

Understanding electron shell structures of atoms is fundamental to explaining the formation of compounds like sodium chloride (table salt).
The outer shell electrons play a pivotal role in chemical reactions.
  - Types of Bonds:
    - Ionic Bonds: Form between metals and non-metals.
    - Covalent Bonds: Form between non-metals.
Irving Langmuir (1919) proposed that noble gases do not form compounds due to their stable electron configuration of eight electrons in the outer shell.
Most elements react to achieve a similar electron arrangement as that of noble gases, which is more stable.
Attaining a stable electron arrangement often occurs through chemical reactions.
Octet Rule: Atoms tend to gain or lose electrons to have eight electrons in their outer shell.
- Duet Rule: Applies to elements that only have electrons in shell 1, which can hold a maximum of two electrons.

Atoms must gain or lose electrons to reach a stable configuration of eight in their outer shells, resulting in a stable electron arrangement resembling the nearest noble gas.
Ions: Atoms that either gain or lose electrons, thus carrying an electric charge.
  - Metal Atoms:
    - Typically lose electrons due to having fewer outer shell electrons.
    - Result in positive ions known as cations (e.g., sodium, magnesium, potassium).
    - Example:
      - Magnesium loses its two outer shell electrons to become a magnesium ion: Mg²⁺.
Non-metal Atoms:
    - Typically gain electrons to complete their outer shell.
    - Result in negative ions known as anions (e.g., chloride).
    - Example:
      - Chlorine gains one electron to form a chloride ion: Cl⁻.
Naming convention for non-metal ions: The suffix "-ide" is added when forming anions from specific non-metals.

The concept of instability transforming into stability is critical in chemistry.
The octet rule serves as a framework for determining stability among particles and predicting chemical reactions.
Open-ended question: Are there more unstable or stable substances in the world?
- Encourages exploration of the world’s chemical diversity.

Bonding Mechanism: Chemical bonding involves electrostatic attraction between oppositely charged particles.
Formation of ionic bonds occurs when cations and anions are attracted to each other:
1. An electron is transferred from a metal atom to a non-metal atom, forming ions.
2. These ions result in the formation of an ionic bond and subsequently an ionic compound.
Example: Sodium chloride
- Electron transfer: Sodium atom loses an electron to chlorine, forming corresponding ions.
Charge Determination Steps for Ions:
  1. Identify the number of valence electrons from the periodic table (group number).
  2. Ascertain how many electrons are lost or gained to achieve a full outer shell.
  3. Write the correct symbol denoting the charge on the ion.

Ionic Compounds: Comprised of numerous cations and anions arranged in a three-dimensional lattice structure, exhibiting alternating charges to neutralize the overall charge of the compound.
Properties of Ionic Compounds:
  - Physical State: Usually solids at room temperature.
  - Melting Points: Typically high due to strong electrostatic forces between ions.
  - Brittleness: Crystalline nature makes them brittle; applying force can cause like-charged ions to align, leading to lattice shattering.
  - Solubility in Water: Often dissolve to form aqueous solutions (aqueous from Latin "aqua" meaning water).
  - Electrical Conductivity: Solutions conduct electricity and so do the compounds when molten due to free-moving ions.

Cations (Positive Ions):
  - Lithium: Li⁺
  - Sodium: Na⁺
  - Magnesium: Mg²⁺
  - Calcium: Ca²⁺
  - Aluminium: Al³⁺
Anions (Negative Ions):
  - Iodine: I⁻
  - Fluorine: F⁻
  - Chlorine: Cl⁻
  - Oxygen: O²⁻
  - Nitrogen: N³⁻

The naming of ionic compounds reflects the ions contained:
1. The metal (cation) retains its name as the first word of the compound.
2. The non-metal (anion) changes to an ‘-ide’ ending to form the second part of the name.