Chemical Bonding: Forces, Structures, and Molecular Properties

Chemical Bonding Fundamentals

Chemical bonding describes how atoms or ions join to form molecules, giant structures, or lattices.

The Octet Rule

Atoms that bond tend to gain, lose, or share electrons until they complete their valence shell with eight electrons.

Primary Types of Chemical Bonds

• Ionic Bonding

  Originates from the electrostatic forces between oppositely charged ions, resulting in the formation of an ionic crystal.

• Covalent Bonding

  Originates when atoms share electrons so that their valence shells are filled, thereby satisfying the octet rule.

Models and Theories of Bonding

• Lewis Model

  The bond is established when attractive forces between atoms are balanced by repulsive forces.

• Standard Electronic Clouds Model

  The charge density between the two nuclei exerts an attractive force on each nucleus, maintaining the structural unit.

Intermolecular Forces (IMFs)

These forces determine the physical properties of molecular substances:

• Dipole-Dipole Forces

  Established between the positive part of one molecular dipole and the negative part of another dipole.

• Dispersion Forces (London Forces)

  Established between molecules due to the formation of instantaneous dipoles, a consequence of electron movement.

• Hydrogen Bonds (H-Bonds)

  High-intensity intermolecular forces established between a hydrogen atom of one molecule and a highly electronegative atom (Fluorine, Oxygen, or Nitrogen) of another molecule.

Bond Energy and Molecular Substances

Bond Energy

Bond energy is the energy required to break a bond. This exact same amount of energy is released when the bond is formed.

Properties of Molecular Substances

Examples of substances and their states at standard conditions:

• Gases: H₂, CO₂.
• Liquids: Br₂, H₂O, CH₃CH₂OH (Ethanol).
• Solids: I₂ (low melting point), Glucose (C₆H₆O₆ or C₁₀H₁₀).

Chemical Properties Assessment

Review of statements regarding chemical properties and structure:

1. Statement: Pure ionic compounds conduct electricity.

   Assessment: (F) False. They conduct electricity only when dissolved or molten.

2. Statement: Pure metals deform without breaking.

   Assessment: (V) True. Layers of cations slide over each other, providing a sliding surface.

3. Statement: Iodine (I₂) is solid and Fluorine (F₂) is gas at room temperature.

   Assessment: (V) True. Both are low molecular substances, but Iodine has a large molecular weight, resulting in stronger dispersion forces and a higher melting point.

4. Statement: The boiling point of Hydrogen Fluoride (HF) is higher than Hydrogen Chloride (HCl).

   Assessment: (V) True. The boiling point increases because HF forms strong Hydrogen bonds.

5. Statement: Molecular solid substances have low melting and boiling points.

   Assessment: (V) True.

6. Statement: Hydrogen Chloride (HCl) dissolved in water conducts electricity.

   Assessment: (V) True. HCl is polar and ionizes in water.

7. Statement: Sodium (Na) has a higher melting point than Cesium (Cs).

   Assessment: (F) False. (Based on the original text's justification: Cs is larger.)

8. Statement: Carbon Tetrachloride (CCl₄) is insoluble in water and soluble in benzene.

   Assessment: (V) True. CCl₄ is nonpolar, making it insoluble in polar water but soluble in nonpolar benzene.

9. Statement: Phosphine (PH₃) can form the phosphonium ion (PH₄⁺).

   Assessment: (V) True. This reaction involves a coordinate covalent (dative) bond.

10. Statement: Silicon Dioxide (SiO₂) is a gas at ambient temperature.

    Assessment: (F) False. SiO₂ is a solid with a high melting and boiling point (giant covalent structure).