Intermolecular Forces Flashcards
(27 cards)
What are the 3 types of intermolecular forces ?
Permanent dipole
Van der waals forces
Hydrogen bonding
What are dipole forces ?
Polar molecules will attract other molecules with permanent dipoles.
How are the strength of dipole forces increased ?
Increasing polarity if the molecules increases the strength of attraction.
What are van der waals forces.
The electrons in the atoms are moving around but are never likely to be spread evenly. This gives a temporary dipole.
The dipole moment will induce a temporary dipole in a neighbouring atom by either attracting or rappelling its electron cloud.
How is the strength of van der waals forces increased ?
The greater the number of electrons, the stronger the attraction and the greater the energy needed to separate out the particles.
What would make van der walla forces very strong.
Atoms with many electrons have a greater attraction and therefore need a lot of energy to separate.
What colour and substance is iodine at room temperature and pressure.
Greyish solid
When is ioidine a greyish solid.
At room temperature and pressure.
What colour vapour does iodine produce when heated?
Purple.
Why does iodine produce a purple vapour when heated ?
Iodine is composed of diatomic molecules which exist in order to make a molecular crystal solids. Each molecules in independent and is only attracted by van der waals forces. This means little energy is needed to separate an iodine molecule.
How much energy is needed to separate an iodine molecule and why.
Little energy because the diatomic molecules are independent and only attracted by van der waals forces.
What type of molecules are in iodine.
Diatomic
What are hydrides
A compound which contains hydrogen and metal.
How does the boiling point of a hydride relate to its Molecular mass.
As molecule mass increases, do does boiling point.
Why do H20, NH3 and HF all have higher boiling points than expected for their Mr ?
All 3 have hydrogen intermolecular bonds which are very strong and require a lot of energy to break.
What is another name for 3-H bonds
Dipole-dipole bonds
What is another name for dipole-dipole bonds ?
3-H bonds.
When do 3-H bonds or dipole-dipole bonds occur ?
They occur when a hydrogen is bonded to nitrogen, oxygen or flouring which are all very electronegative.
The H only has 2 electrons in the covalent bond and when these are pulled away from the H atom, the H nucleus is exposed.
The H bonds is then the attraction between the lone pair in N/O/F and the slightly positive neighbouring H atom.
What atoms create dipolar-dipolar bonds with hydrogen ?
Oxygen
Nitrogen
Fluorine
What does the size of F/O and N mean for dipole-dipole bonds ?
They are all small atoms so lead to a high charge density which makes the internolecular attraction greater and therefore increases melting and boiling points of the molecule.
What atoms have a high charge density and why.
Oxygen, fluroine and nitrogen because they are all small atoms.
How many bonds does water have ? And what type of bonds ?
4 hydrogen bonds
What formation does water have ?
Tetrahedral
Why does ice float ?
The volume of ice is larger than water therefore meaning ice is less dense than water and will float.
