Intramolecular Forces

Intermolecular Forces DLD Day Assignment

by Jessica Holmes

​Remember?

​Three types of bonding

• Ionic Bonding

  • A metal cation donates electrons to the nonmetal anion

  • Held together by electrostatic attraction

• Nonpolar Covalent Bonding

  • The equal sharing of electrons between nonmetals that have similar electronegativities

• Polar Covalent Bonding

  • The unequal sharing of electrons between nonmetals that have very different electronegativities

• Metallic Bonding

  • Positively charged metal cations are held together in a lattice, which allows their electrons to move around the cations like a sea

​INTRA – WITHIN

INTER – BETWEEN

​Intramolecular forces         Intermolecular forces

Multiple Choice

Intermolecular forces are the forces

• within molecules
• between molecules

Multiple Choice

Intramolecular forces are the forces

• within molecules

• between molecules

​Intermolecular Forces

​Attractive forces between molecules and atoms that allow them to consolidate into liquids and solidify into solids

• Examples:  

  • Dipole – dipole interactions

    • Happens between polar molecules

• Interactions occur when the partial charges formed within one molecule are attracted to an opposite partial charge in a nearby molecule.

​Dipole-Dipole Interactions

​ Two polar substances will orient themselves to attract to each other. 

 Sugar will dissolve in water because both are polar molecules.

​London Dispersion Forces

​London Dispersion forces

Nonpolar molecules can become momentarily polar, due to movement of electrons

​London Dispersion Forces

​Since the bonds are weak, the materials tend to be fragile and easily disrupted.

• Dry ice is crumbly and does not hold its form well due to its crystalline structure being loosely assembled by LDF.

​Larger Molecules Have Greater London Dispersion Forces

• ​The larger a molecule, the further electrons can travel when being repelled by electrons from other molecules.

• Larger molecules have larger dispersion forces, which means they cling to each other more and thus will stick together at higher temperatures.

​Dipole-Induced Dipole

​If a polar molecule comes close to a non-polar molecule, it will repel the electrons of the nonpolar one and thus will induce a dipole.

• They will then be attracted to each other. 

​

​Although the attraction is much weaker than two polar molecules would have.

​Dipole-Induced Dipole

​Non-polar gases with lone-pairs like O₂ , CO₂ , and N₂ will dissolve slightly in water because the polar water molecules will induce the dipole of the gas molecules.

​Hydrogen Bonding

​Strong attraction between electronegative atoms (N, O or F) and hydrogen, due to a large electronegativity difference

​Hydrogen Bonding is the Key to Life

​ Hydrogen bonding is what allows proteins to hold their shape and DNA to remain a double-helix.

​Why Do Water and Oil Not Mix?

​Water displays hydrogen bonding intermolecular force attraction with itself

• But, oil is a non-polar molecule. 

• Being non-polar, there are no ends for waters to attach. 

• Water attach to each other and simply push oil out of the way.

​Ion-Dipole Forces

​Ion–dipole interactions is the attraction between the partial charges on polar covalent molecules and the full ions of ionic compounds

• The strength of these forces is what makes it possible for ionic substances to dissolve in polar solvents (why salt can dissolve in water)

​IMFs AND PHYSICAL PROPERTIES

​The STRONGER the forces between particles/molecule

• The HIGHER the melting point - the temperature at which a solid becomes a liquid

• The HIGHER the boiling point - the temperature at which a liquid becomes a gas

• The LOWER the vapor pressure - aka, the harder it is to evaporate

• The HIGHER the viscosity 

  • The ability of a fluid to flow

    • The more easily a fluid flows, the lower the viscosity

• The HIGHER the surface tension

  • Added attractive force per molecule at the surface of a liquid

  • Which is part of why the vapor pressure is lower

​Ranking Intermolecular Forces

• ​London Dispersion Forces

• Dipole-Induced Dipole

• Dipole-Dipole

• Hydrogen Bonding

• Ion-Dipole

Multiple Choice

This is an example of a(n) __________.

• Hydrogen Bonding

• Dipole

• Nonpolar Molecule

• Intermolecular Force

Multiple Choice

Which intermolecular force requires hydrogen and one of the following: nitrogen, oxygen, fluorine?

• Dipole-dipole

• Hydrogen bonding

• London dispersion forces

Multiple Choice

Does CH₄ have hydrogen bonding?

• yes
• no

Multiple Choice

Does NH₃ have hydrogen bonding?

• yes
• no

Multiple Choice

What kind of force is the arrow pointing to?

• Intramolecular Force

• Intermolecular Force

Multiple Choice

The weaker the intermolecular forces of a substance the _____________ the boiling point

• higher

• lower

Multiple Choice

London forces are stronger in heavier atoms or molecules, and weaker in lighter atoms or molecules.  Which of these has the strongest London forces?

• F₂
• Br₂
• I₂
• Cl₂

Multiple Choice

Does HF have hydrogen bonding?

• yes
• no

Multiple Choice

What information do we look for on the periodic table if we  want to examine intermolecular forces?

• atomic mass
• atomic number
• electronegativity
• ionization 

Multiple Choice

Type of intermolecular force present in I₂, Br₂, and Cl₂.

• dipole dipole
• H-bond
• dispersion
• metallic

Multiple Choice

H₂S has what kind of intermolecular force?

• dipole dipole
• dispersion
• H-bond
• ionic

Multiple Choice

Intermolecular force present in HCl?

• dipole dipole
• dispersion
• H-bond
• ionic

Multiple Choice

Intermolecular force present in Cl₂?

• dipole dipole
• H-bond
• dispersion
• metallic

Multiple Choice

In a polar covalent bond, the electrons gather around...

• Mostly the atom with the greatest electronegativity

• The atom with the lowest electronegativity

• Each atom equally

• Only the atom with the greatest electronegativity

Multiple Choice

In a nonpolar covalent bond, the electrons gather around...

• Mostly the atom with the greatest electronegativity

• The atom with the lowest electronegativity

• Each atom Equally

• Only the atom with the greatest electronegativity