Chapter 6 - Shapes of molecules and intermolecular forces Flashcards
What is the electron-pair repulsion theory?
Used to predict shapes of molecules or ions
Electron pairs repel each other so they are as far apart as possible
Lone pairs repel more than bonding pairs
What is bond length?
Distance between the nuclei of the two bonded atoms
What is bond angle?
Angle between two covalent bonds
Describe the linear shaped molecule.
EP - 2
BP - 2
LP - 0
180°
e.g. CO2
Describe the trigonal planar shaped molecule.
EP - 3
BP - 3
LP - 0
120°
e.g. BF3
Describe the non-linear shaped molecules.
EP - 3
BP - 2
LP - 1
119°
e.g. SO2
OR
EP - 4
BP - 2
LP - 2
104.5°
e.g. H2O
Describe the tetrahedral shaped molecule.
EP - 4
BP - 4
LP - 0
109.5°
e.g. CH4
Describe the pyramidal shaped molecule.
EP - 4
BP - 3
LP - 1
107°
e.g. NH3
Describe the trigonal bipyramidal molecule.
EP - 5
BP - 5
LP - 0
90° and 120°
e.g. PF5
Describe the octahedral molecule.
EP - 6
BP - 6
LP - 0
90°
e.g. SF6
Describe the distorted square pyramid molecule.
EP - 6
BP - 5
LP - 1
89°
e.g. ClF5
Describe the square planar molecule.
EP - 6
BP - 4
LP - 2
90°
e.g. XeF4
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond
Which element has the highest electronegativity and why?
Fluorine
Small atomic radius (less repulsion)
Low electron shielding (less repulsion)
Relatively high nuclear charge to outweigh the others to attract the electrons
What is a polar bond?
Then the electron pair is shared unequally between the bonded atoms due to a difference in electronegativity
Making there permanent dipoles with partially positive/negative charges on each end.
How can you determine whether a molecule is bonded ionically or covalently?
Electronegative difference
<1.8 = covalent bond
> 1.8 = ionic bond
What is a polar molecule?
Polar bonds need to reinforce each other in into one direction to create poles
If they cancel each other out then they are no longer polar
Just because a molecule has polar bonds doesn’t make it a polar molecule
What are intermolecular forces?
Weak interactions between dipoles of different molecules.
What are the three types of intermolecular forces?
Induced dipole-dipole forces (London forces)
Permanent dipole-dipole forces
Hydrogen bonding
Describe induced dipole-dipole forces.
Between all molecules
Movement of electrons in a molecule is random meaning an instantaneous dipole can form which will induce a force upon a neighboring molecule, therefore attraction each other and forming intermolecular forces
Relatively weakest of the intermolecular forces
Describe permanent dipole-dipole forces.
Occurs in polar molecules
Stronger than London forces in the same molecule
Describe hydrogen bonding.
Special permanent-permanent dipole force
Must involve an electropositive hydrogen and an electronegative O, N or F
The electronegative atom must have a lone pair
Strongest type of intermolecular force
Describe the anomalous trends of water.
Solid state is less dense than the liquid state - hydrogen bonding holds the molecules apart in the lattice structure
Relatively high melting and boiling point - hydrogen bonding is stronger than London forces so it has higher energy required compared to similar molecules
What are the simple molecular lattices?
Solid structures made up of simple molecules
e.g. Iodine
Molecules held together by weak intermolecular forces
Atoms in a molecules held together by strong covalent bonds
Why do simple molecular substances have low boiling/melting points?
Weak intermolecular forces
What is the solubility of non-polar simple molecular substances?
Soluble in non-polar substances - Intermolecular forces form between the two substances and these weaken the IMFs in the simple molecular substance and it dissolves into the solvent
Insoluble in polar substances - Very little interactions with each other
What is the solubility of polar simple molecular substances?
Solubility depends on the strength of the dipoles
Many do dissolve in both polar and non-polar substances as they attract each other
What is the electrical conductivity of simple molecular substances?
No mobile charged particles therefore there is nothing to complete an electrical circuit
They do not conduct electricity
