Shapes of molecules and ions (6) Flashcards
Electron repulsion
When you have a pair of electrons they will repel each other, but will also repel other electron pairs in the molecule so the bonded pairs will position themselves as far apart as possible which gives the molecule a specific shape
Which repels more, bonded or lone pairs?
Lone pairs will repel a lot more than a bonded pair so they will push the bonded pairs further apart from it and they will be moved closer together
Tetrahedral
4 bonded pairs, 0 lone pairs
109.5 angle
Trigonal planar
3 bonded pairs 0 lone pairs
120 angle
Linear
2 bonded pairs, 0 lone pairs
180 angle
Pyramidal
3 bonded pairs, 1 lone pair
107 angle
Non-Linear
2 bonded pairs, 2 lone pairs
104.5 angle
Trigonal Bipyramidal
5 bonded pairs, 0 lone pairs
120 and 90 angles
Octahedral
6 bonded pairs, 0 lone pairs
90 angle
T-shaped
3 bonded pairs, 2 lone
<90 angle
Umbrella
5 bonded pair, 1 lone pair
90, <90 angle
What is electronegativity?
The ability of an nuclei of an atom in a covalent bond to attract the shared pair of electrons
What affects the electronegativity of an atom?
How big the nuclear charge is and how big the atomic radius is
How is electronegativity measured?
The Pauling Scale
What are the most electronegative elements?
Fluorine, nitrogen, oxygen and chlorine
How do you know if it’s an ionic or covalent bond using the Pauling scale?
If it’s 0 its a pure covalent which means atoms of the same element are bonded together.
If it’s 0-1.8 its a polar covalent which means the shared pair of electrons are closer to one atom than the other
If it’s more than 1.8 it’s ionic because the shared pair of electrons is a lot closer to one of the atoms than the other until they become accepted by it to form ions.
When will a bond be non-polar?
When the two atoms in a covalent bond are the same or have very similar electronegativities
When will a bond be polar?
When both of the atoms have different electronegativity values which means the electronegative atom will have a stronger attraction to the shared pair of electrons and so will create a partially positive and negative dipole.
Is water a polar molecule, why?
Water is a polar molecule because O-H is a polar bond. The oxygen is far more electronegative than hydrogen so attracts the pair of electrons and becomes partially negative while hydrogen becomes partially positive. Because water is a non-linear molecule, the two polar bonds don’t cancel.
Is CO2 a polar molecule, why?
CO2 is not a polar molecule. This is because even though C=O is polar, the molecule is linear so the dipoles act in opposite directions and get cancelled out.
Why are ionic lattices soluble in polar solvents?
Because the partial charges on the dipole can attract the ions in the lattice and break it apart. E.g NaCl will dissolve in water because the partially positive H will attract the Cl- and the partially negative O will attract the Na+
What is an intermolecular force?
Weak interactions between dipoles of different molecules. These could be London forces, permanent dipole-dipole interactions and hydrogen bonding
What are London forces?
They are induced dipole-dipole interactions and weak intermolecular forces that occur between all molecules
How are London forces created?
Electrons are constantly moving around so instantaneous dipoles are being created in molecules. This then triggers instantaneous dipoles in other molecules and they attract each other. In the next instant, the dipole may disappear.