STRUCTURE AND BONDING

  Al D. Deacon 

Founder: Gold'N Geniuz 

Physicist and Educator  

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1. Formation of Ionic and Covalent Bonds

Ionic Bonding:

• Definition: A bond formed by the transfer of electrons from a metal to a non-metal.
• Process:
  • Metals lose electrons to form cations (positively charged ions).
  • Non-metals gain electrons to form anions (negatively charged ions).
  • The electrostatic attraction between oppositely charged ions creates a strong bond.
• Example: Sodium (Na) donates one electron to chlorine (Cl) → NaCl (sodium chloride).
• Properties: High melting and boiling points, soluble in water, conducts electricity in molten or dissolved state.

Covalent Bonding:

• Definition: A bond formed when two non-metal atoms share one or more pairs of electrons.
• Types of Covalent Bonds:
  • Single bond: One pair of electrons shared (H₂, Cl₂).
  • Double bond: Two pairs of electrons shared (O₂).
  • Triple bond: Three pairs of electrons shared (N₂).
• Example: Water (H₂O) → Oxygen shares electrons with two Hydrogen atoms.
• Properties: Low melting and boiling points, does not conduct electricity, often found in gases, liquids, or soft solids.

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2. Predicting Bond Type Based on Atomic Structure

• Electronegativity Difference:
  • >1.7 → Ionic bond (e.g., NaCl).
  • 0.4 – 1.7 → Polar covalent bond (e.g., H₂O).
  • <0.4 → Non-polar covalent bond (e.g., Cl₂).
• Periodic Trends:
  • Metals (left side) lose electrons → ionic bonds.
  • Non-metals (right side) gain/share electrons → covalent bonds.

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3. Writing Formulae for Ions, Molecules, and Formula Units

Ions:

• Cations (+): Metals lose electrons → Na⁺, Mg²⁺.
• Anions (-): Non-metals gain electrons → Cl⁻, O²⁻.

Molecules:

• Formed by covalent bonding → H₂O, CO₂, NH₃.

Formula Units (Ionic Compounds):

• Represent the simplest ratio of ions → NaCl, MgO, CaF₂.
• Crisscross Method for neutralizing charge:
  • Mg²⁺ and Cl⁻ → MgCl₂.
  • Al³⁺ and O²⁻ → Al₂O₃.

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4. Metallic Bonding

• Definition: A bond formed between metal atoms where valence electrons are delocalized and move freely.
• Structure: Positive metal ions surrounded by a “sea of electrons.”
• Properties of Metals Due to Bonding:
  • Malleability & Ductility: Layers of atoms slide without breaking.
  • Electrical Conductivity: Free electrons move easily.
  • High Melting and Boiling Points: Strong electrostatic attraction.

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5. Types of Crystals

Ionic Crystals

• Composed of ions held by strong electrostatic forces.
• Example: NaCl (table salt).
• Properties: Hard, brittle, high melting point, conducts electricity in solution.

Simple Molecular Crystals

• Formed by molecules held together by weak intermolecular forces (Van der Waals, dipole-dipole, hydrogen bonding).
• Example: Iodine (I₂), dry ice (CO₂).
• Properties: Soft, low melting point, does not conduct electricity.

Giant Molecular Crystals

• Atoms are bonded by strong covalent bonds in a large network.
• Examples: Diamond (C), Quartz (SiO₂).
• Properties: Very high melting points, hard, does not conduct electricity (except graphite).

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6. Distinguishing Ionic and Molecular Solids

Property	Ionic Solids (e.g., NaCl)	Molecular Solids (e.g., I₂, CO₂)
Bonding	Electrostatic forces	Weak intermolecular forces
Melting/Boiling Point	High	Low
Conductivity	Conducts in solution	Non-conductive
Hardness	Hard, brittle	Soft

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7. Structure and Properties of NaCl, Diamond, and Graphite

Sodium Chloride (NaCl)

• Structure: Giant ionic lattice.
• Properties:
  • High melting/boiling point (strong electrostatic forces).
  • Soluble in water.
  • Conducts electricity when molten or dissolved.
• Uses: Food seasoning, de-icing roads, and making chlorine gas.

Diamond (Carbon, C)

• Structure: Giant covalent lattice, each C bonded to 4 others.
• Properties:
  • Very hard (used in cutting tools).
  • High melting/boiling point.
  • Does not conduct electricity (no free electrons).
• Uses: Jewelry, drill bits, and industrial cutting tools.

Graphite (Carbon, C)

• Structure: Layers of carbon atoms bonded in hexagonal rings, weak Van der Waals forces between layers.
• Properties:
  • Soft and slippery (layers slide over each other).
  • Conducts electricity (delocalized electrons).
  • High melting point.
• Uses: Pencil lead, lubricants, electrodes.

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8. Allotropy

• Definition: The existence of an element in different structural forms in the same physical state.
• Examples:
  • Carbon → Diamond, Graphite, Fullerene.
  • Oxygen → O₂ (oxygen gas), O₃ (ozone).
  • Phosphorus → White phosphorus, Red phosphorus.

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