2.2.2 Electronegativity And Intermolecular Forces Flashcards
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond.
Due to electronegativity there is a spectrum of ionising and covalency in a chemical bond.
What is the spectrum of charges? (Informal)
Ionic bonding —————polar covalent bonding ————non-polar covalent bonding
(Full charges). (Partial charges). (Electronically symmetrical)
What is a permanent dipole?
A small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms
What is a polar covalent bond?
Has a permanent dipole
What is a polar molecule?
Has a an overall dipole when all permanent dipoles and molecular shape are considered
Is CCl4 polar or non-polar?
- each C-Cl bond is polar
- however a CCl4 molecule is symmetrical
- therefore dipoles ACT IN DIFFERENT DIRECTIONS and so cancel out
- hence CCl4 is non-polar
What is an intermolecular force?
An attracting force between neighbouring molecules
What is a permanent dipole-dipole force?
A weak attractive force between PERMANENT DIPOLES in neighbouring polar molecules
What are London forces?
A temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles
Attractive forces between induced dipoles in neighbouring molecules.
How is an induced dipole created?
The electrons of an uncharged molecule are attracted by the slightly positive and negative ends of an exsisting dipole.
An induced dipole will orient itself so that the + end of one is attracted to the - end of the other
More electrons = more fluctuations in electron cloud possible = greater London forces
What is a hydrogen bond?
A strong dipole-dipole interaction between an electron deficient hydrogen atom:
O-H, N-H or F-H (only bonded to highly electronegative atoms - electron deficient)
AND a lone pair of electrons on a highly electronegative atom (H-O, H-N) on a different molecule
See notes for diagram (quite specific)
Why is ice less dense than water?
- water molecules arrange themselves into an orderly pattern and hydrogen bonds form between the molecules
- ice has an open lattice with hydrogen bonds holding the water molecules apart
- ice is less dense than water, hence floats
Why does water have a higher than expected mpt and bpt?
- hydrogen bonds are stronger than other IM forces
- extra strength of forces has to be overcome to melt or boil H2O
- higher mpt and bpt than if no hydrogen bonds present
Why does water have surface tension?
- extra IM bonding from hydrogen bonds = relatively high surface tension and viscosity of water
