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Flashcards in Intermolecular Forces Deck (30):

What are intermolecular forces?

Weak interactions between molecules of different molecules.


What are the three main types of intermolecular forces?

Induced dipole-dipole interactions (London forces)
Permanent dipole-dipole interactions
Hydrogen bonding


What type of property are intermolecular forces largely responsible for?

Physical properties


Give an example of a physical property?

Melting and boiling points.


What type of properties do covalent bonds determine?

The identity and chemical reactions of molecules.


List the intermolecular forces in order of strength.

London forces
Permanent dipole-dipole interactions
Hydrogen bonds


What is stronger, intermolecular forces of single covalent bonds?

Single covalent bonds


What type of molecules do London forces exist between?

They exist between all molecules, regardless of polarity.


What are London forces?

Weak intermolecular forces that exist between all molecules. They act between induced dipoles indifferent molecules.


Explain the origin of induced dipoles.

Movement of electrons produces a changing dipole in a molecule.
At any instant, an instantaneous dipole exist, but its position is constantly shifting.
The instantaneous dipole induces a dipole on a neighbouring molecule.
The induced dipole induces further dipoles on neighbouring molecules, which then attract one another.


Are induced dipoles temporary or permanent?



What do induced dipoles result from?

The interactions of electrons.


What happens to the strength of London forces as E number of electrons in the molecule increases?

The more electrons the:
Larger the induced dipole
The greater the induced dipole-dipole interactions
The stronger threat traction forces between the molecules


Why does the boiling point increase down the noble gases?

The larger number of electrons the larger the induced dipoles.
More energy is then needed to overcome the intermolecular forces, increasing the boiling point.


What do van der Waals forces describe?

This term is used to describe both induced and permanent dipole-dipole interactions.


What do permanent dipole-dipole interactions act between?

Permanent dipole-dipole interactions act between the permanent dipoles in different polar molecules.


What increases the boiling and melting points of molecules?

The permanent dipole-dipole interactions.


What is a simple molecular substance?

This is made up of small molecules containing a definite number of atoms with a definite molecular formula.


What do simple molecules form in their solid state?

A regular structure called a simple molecular lattice.


What are the bonds like in a simple molecular lattice?

The molecules are held in place by weak intermolecular forces.
The atoms within each molecule are bonded together strongly by covalent bonds.


Why do simple molecular substances have low melting and boiling points?

The weak intermolecular forces can be broken by the energy present at low temperatures.


What state are simple molecular substances in at low temperatures?

They can be solid, liquid or gases.


How can you solidify simple molecular structures?

By lowering the temperatures.


What happens when a simple molecular lattice is broken apart during melting?

Only the weak intermolecular forces break.
The covalent bonds are strong and do not break.


What two categories do simple molecular substances fit into?

Polar and non-polar.


What happens when a non-polar simple molecular compound is added to a non-polar solvent?

Intermolecular forces form between the molecules and the solvent.
These interactions weaken the intermolecular forces in the molecular lattice.
The intermolecular forces break and the compound dissolves.
Non-polar simple molecular substances tend to be soluble in non-polar solvents.


What happens when a non-polar simple molecular substance is added to a polar solvent?

There is little interaction between the molecules in the lattice and the solvent molecules as the intermolecular bonding within the polar solvent is too strong to be broken.
Simple molecular substances tend to be insoluble in polar solvents.


Why might polar covalent substances dissolve in polar solvents?

The polar solvent molecules and the polar solute molecules a can attract each other.


What does the solubility of polar simple molecular substances depend on?

The strength of the dipole.


Why are simple molecular substances not conductors of electricity?

There are no delocalised electrons so there are no charged molecules that can move, therefore the electrical circuit can not be completed.