Intermolecular Forces

• What is the definition of electronegativity?

  Electronegativity is the ability of an atom to attract electrons towards itself in a covalent bond.
• Which element is the most electronegative?

  Fluorine
• How does the difference in electronegativity affect bond polarity?

  The larger the difference in electronegativity, the more polar the bond becomes.
• What indicates a polar bond between hydrogen and chlorine?

  The chlorine atom pulls electrons towards itself, creating a partial negative charge (δ-) and the hydrogen a partial positive charge (δ+).
• Why is a molecule of chlorine (Cl₂) considered non-polar?

  Because both chlorine atoms have the same electronegativity, resulting in equal sharing of electrons.
• What is the relationship between uneven charge distribution and polar molecules?

  Uneven charge distribution leads to polar molecules, as seen in water.
• What are Van der Waals forces also known as?

  Induced dipole-dipole forces.
• What type of forces exist between atoms and molecules in Van der Waals interactions?

  Weak forces between molecules, not bonds.
• How do the size of molecules affect Van der Waals forces?

  Larger molecules have more electrons and thus stronger Van der Waals forces.
• What happens when boiling a liquid in terms of intermolecular forces?

  Weak Van der Waals forces are broken, not covalent bonds.
• What is the effect of branching in hydrocarbons on boiling points?

  Branched hydrocarbons have lower boiling points due to weaker Van der Waals forces.
• What are dipole-dipole interactions?

  Interactions between molecules that have a permanent dipole.
• What is an example of a molecule with a permanent dipole?

  Hydrogen chloride (HCl)
• How can you demonstrate the polarity of water using a charged rod?

  A charged rod will attract a stream of water, showing the alignment of polar molecules.
• What is hydrogen bonding and when does it occur?

  Hydrogen bonding occurs when hydrogen is bonded to highly electronegative elements like nitrogen, oxygen, or fluorine.
• What is the unique property of ice compared to most substances when cooled?

  Ice expands and becomes less dense when cooled.
• Why does HF have a higher boiling point than HCl?

  HF can form hydrogen bonds, requiring more energy to break them compared to HCl.
• How do Van der Waals forces compare to dipole-dipole interactions?

  Dipole-dipole interactions are stronger than Van der Waals forces.
• What are the characteristics of polar and non-polar molecules?

  • **Polar Molecules**:
  • Have a permanent dipole.
  • Dissolve well in polar solvents (e.g., water).
  • Examples: Water (H₂O), Hydrogen chloride (HCl).

  
  

  • **Non-Polar Molecules**:
  • No permanent dipole.
  • Dissolve well in non-polar solvents (e.g., hydrocarbons).
  • Examples: Oxygen (O₂), Methane (CH₄).
• What are the types of intermolecular forces and their relative strengths?

  1. **Van der Waals Forces**:

  • Weakest intermolecular forces.
  • Present in all molecules.

  
  

  1. **Dipole-Dipole Interactions**:

  • Stronger than Van der Waals.
  • Occur in polar molecules.

  
  

  1. **Hydrogen Bonds**:

  • Strongest intermolecular forces.
  • Occur between hydrogen and highly electronegative elements (N, O, F).
• How does the difference in electronegativity affect bond polarity?

  The larger the difference in electronegativity, the more polar the bond becomes.
• What is a polar bond?

  A polar bond occurs when there is a difference in electronegativity between the atoms involved.
• Why is the H-Cl bond considered polar?

  Chlorine is more electronegative than hydrogen, pulling electrons closer to itself.
• Why is a molecule of chlorine (Cl₂) non-polar?

  Both chlorine atoms have the same electronegativity, resulting in equal sharing of electrons.
• What type of intermolecular force is known as Van der Waals forces?

  Induced dipole-dipole interactions.
• What are Van der Waals forces?

  Weak forces that exist between atoms and molecules due to temporary dipoles.
• How do Van der Waals forces affect the boiling point of a substance?

  The larger the molecule, the stronger the Van der Waals forces, leading to a higher boiling point.
• What happens to the intermolecular forces when boiling a liquid like water?

  Weak Van der Waals forces are broken, not the covalent bonds.
• What is the strongest type of intermolecular force?

  Hydrogen bonding.
• What conditions lead to hydrogen bonding?

  Hydrogen bonding occurs when hydrogen is bonded to highly electronegative elements like nitrogen, oxygen, or fluorine.
• How does ice differ from most substances when cooled?

  Ice expands and becomes less dense due to hydrogen bonding, allowing it to float on water.
• What is the relationship between boiling points and hydrogen bonding?

  Molecules capable of hydrogen bonding generally have higher boiling points due to stronger intermolecular forces.
• How does polarity affect solubility?

  • **Polar Molecules**: Dissolve well in polar solvents (e.g., water).
  • **Non-Polar Molecules**: Dissolve well in non-polar solvents (e.g., hydrocarbons).
• What is a dipole in chemistry?

  A dipole is the difference in charge between the two atoms of a covalent bond caused by a shift in electron density due to electronegativity differences.
• What is electron pair repulsion?

  Electron pair repulsion is the repulsion that exists between electron pairs due to their negative charge, causing them to position themselves as far apart as possible around a central atom.

  
• What are electrostatic forces?

  Electrostatic forces are the strong forces of attraction between oppositely charged ions.
• What is hydrogen bonding?

  Hydrogen bonding is an interaction between a hydrogen atom and an electronegative atom, commonly nitrogen, fluorine, or oxygen.
• How do hydrogen bonds compare to other types of bonds?

  Hydrogen bonds are stronger than van der Waals and dipole-dipole forces but weaker than ionic and covalent bonds.
• What are intermolecular forces?

  Intermolecular forces are the forces which exist between molecules, impacting physical properties like boiling and melting points.
• What are permanent dipole-dipole forces?

  Permanent dipole-dipole forces occur when molecules with polar covalent bonds interact with dipoles in other molecules.