MR - Electronegativity and Intermolecular Forces Flashcards
Define electronegativity
The ability to attract bonding electrons in a covalent bond
What scale is electronegativity measured on and what do higher values mean?
The Pauling scale
The higher the value, the more electronegative the element is
State the most electronegative element
Fluorine
although Oxygen, Nitrogen and Chlorine are also strongly electronegative
Describe the trend in electronegativity across the periods
Electronegativity increases across the periods
Describe the trend in electronegativity down the groups
Electronegativity decreases down the groups (ignoring noble gasses)
Explain polarity of covalent bonds
In a covalent bond between two atoms of different electronegativities, the bonding electrons are pulled towards the more electronegative atom. This makes the bond polar
Explain why a molecule’s shape and polarity effect whether it has a permanent dipole
- Simple molecules (like HCl), polar bonds give the whole molecule a permanent dipole
- More complicated molecules may have several polar bonds. If they are arranged so they point in opposite directions, they’ll cancel each other out (non-polar overall)
- If the polar bonds all point in roughly the same direction, then the molecule is polar
- Lone pairs of electrons on the central atom also have an effect on the overall polarity
Name the 3 types of intermolecular bonds
- Permanent Dipole - Permanent Dipole
- Instantaneous Dipole - Induced Dipole
- Hydrogen Bonding
Give the 3 types of intermolecular bonds in order of strength from strongest to weakest
- Hydrogen
- PD-PD
- ID-ID
Describe PD-PD bonding
The delta + and - charges on polar molecules cause a weak electrostatic force of attraction between molecules
Describe ID-ID bonding
- Electrons in charge cloud are always moving quickly. At one moment, the electrons in a bond are more likely to be one side than the other
- This dipole can induce a temporary dipole in adjacent molecules. The molecules are then attracted to each other
- Because the electrons are constantly moving, dipoles are being created and destroyed all the time.
Give 3 factors that effect the strength of intermolecular forces
- The polarity of the molecules
- The size of the molecule
- The shape of the molecule (e.g. branching)
Describe hydrogen bonding
- Hydrogen is bonded to an electronegative element drawing the bonding electrons away from Hydrogen
- This bond is polarised so Hydrogen forms an electrostatic attraction to a lone pair of electron of other molecules