1.3(P2) Shapes And Forces
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What are the 5 basic shapes of molecules?
Linear Trigonal Planar Tetrahedral Trigonal Bipyramidal Octahedral
How do we work out the shape?
Identify the central atom Determine how many … are around the central atom: Electrons Electron Pairs Bonding Pairs Lone Pairs Then arrange the electron pairs as far apart as possible Name the shape and suggest the bond angle
What are the possible shapes with 2 electron pairs? Bonding angles?
Linear - 2 bonding pairs 180 °
What are the possible shapes with 3 electron pairs? Bonding angles?
Trigonal Planar - 3 bonding pairs V-shaped - 2 bonding pair, 1 lone pair 120 ° 117.5 °
What are the possible shapes with 4 electron pairs? Bonding angles?
Tetrahedral - 4 bonding pairs Trigonal Pyramidal - 3 bonding pairs, 1 lone pair V-shaped - 2 bonding pairs, 2 lone pairs 109.5 ° 107 ° 104.5 °
What are the possible shapes with 5 electron pairs? Bonding angles?
Trigonal Bipyramidal - 5 bonding pairs See-saw - 4 bonding pairs, 1 lone pair T-shaped - 3 bonding pairs, 2 lone pairs 120 ° , 90 ° 117.5 ° , 87.5 ° 120 ° , 86 °
What are the possible shapes with 6 electron pairs? Bonding angles?
Octahedral - 6 bonding pairs Square Pyramidal - 5 bonding pairs, 1 lone pair Square Planar - 4 bonding pairs, 2 lone pairs 90 ° 87.5 ° 90 °
What is electronegativity?
The power of an atom to attract the electron density in a covalent bond towards itself
What are the trends of electronegativity?
Electronegativity increases left to right across a period Electronegativity increases up a group
What is significant about noble gases?
They don’t form compounds therefore have no electronegativity
What are intermolecular forces?
Forces between all molecules in covalent bonding in liquids and solids
What are the intermolecular forces in order of strength?
Hydrogen bonding Permanent dipole-dipole interaction Van der Waals force
What are Van der Waals?
Weakest type of intermolecular force present in all molecules but the strongest type of force that acts on non-polar molecules
What does the strength of the van der Waals depend on?
Size of the molecules As larger molecules have more electrons hence stronger attractions
What causes van der Waals?
Temporary partial charges on the molecules occur due to fluctuating electron density which creates a temporary induced dipole Therefore the temporary dipole and the temporary induced dipole causes the molecules to be attracted
What is van der Waals also called?
Dispersion Forces
What are permanent dipole dipole forces?
They occur between polar molecules (molecules with an overall permanent dipole moment due to difference in electronegativity)
How do permanent dipole dipole forces occur?
A molecule has a high electron density due to greater electronegativity This causes a permanent dipole
What can permanent dipole dipole forces be affected by?
Van der Waal forces but the permanent dipole dipole interaction is likely to be stronger
What is hydrogen bonding?
A specific type of permanent dipole dipole which only occurs between molecules containing hydrogen bound to: Nitrogen Oxygen Fluorine
Why is hydrogen bonding special?
There is a greater dipole due to the large difference in electronegativity between hydrogen and N, O or F
What must you show on intermolecular force diagrams?
The covalent bonds The delta partial charges ALL the lone pairs A dashed line between the element to a lone pair
What is the effect of hydrogen bonding on the boiling points of Hydrides?
Those with hydrogen bonding have higher boiling points Big drop down the groups as van der Waals are weaker but slight incline as the go from there as the size of the molecules increase
What has the highest boiling point out of hydrides?
Water It has the strongest attraction It can form more hydrogen bonds