5. Inter-molecular attractions and melting and boiling points Flashcards
What is a covalent bond? (Nat 5)
A shared pair of electrons
What is a non-polar (Pure) covalent bond?
An equal sharing of electrons between atoms with very similar en values
What is a polar covalent bond?
A n unequal sharing of electrons caused by atoms forming covalent bond having an en difference >0.5 and <2.0
How does electronegativity difference link to “covalent character” ?
The lower the electronegativity difference, the greater the covalent character
What is a dipole?
A separation in charge within a molecule
How do London Dispersion Forces arise?
- Electron Wobble
- Momentary separation of charge called Temp Dipole
- Induced dipole
- Electrostatic attraction between dipoles is LDF
Why were the Noble Gases used to show existence of intermolecular attractions called LDF?
There is no other bonding going on in the Noble gases so differences in boiling points had to be down to attractions between atoms.
Why do boiling points of Noble Gases increase going down group
- More electrons in atoms leads to greater cloud wobble
- leads to greater separation of charge and larger dipoles
- Electrostatic attraction between dipoles increases
- requires more energy to break them
- Boling points increase
Why do boiling points of halogens increase going down group?
- More electrons in molecules leads to greater cloud wobble
- leads to greater separation of charge and larger dipoles
- Electrostatic attraction between dipoles increases
- requires more energy to break them
- Boling points increase
Why does sulphur have a higher melting point than phosphorous?
- Sulphur exists as S8 molecules and phosphorous as P4
- Greater number of electrons in molecule leads to greater dipoles
- Electrostatic attractions is therefore larger between di[poled molecules and requires more energy to break them
- Melting point is therfore higher
What is a hydrogen bond?
A strong dipole-dipole electrostatic attraction between molecules where h is bonded to a small, highly electronegative atom.
Which 3 elements, if directly bonded to a H atom, will cause H-bonding to arise?
Nitrogen
Oxygen
Fluorine
How would you show a H-bond between 2 water molecules?
What is the bonding continuum?
The type of bonding is determined by the difference in electronegativity between the elements involved.
How does electronegativity difference link to “Ionic character” ?
The greater the electronegativity difference, the greater the ionic character
