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Chapter 6 - Shapes of molecules I - Coggle Diagram
Chapter 6 - Shapes of molecules I
Electron pair repulsion theory
Electron pairs repel one another as electrons have negative charge, this means they/re arranged as far apart as possible
Arrangement minimises repulsions
Shapes of molecules
Wedges
Solid line - bond in the plane of the paper
Solid wedge - comes out of the plane of the paper
Dotted wedge - goes into the plane of the paper
Bonded/ lone pair repulsions
Lone pair is slightly closer to the central atom, also occupies more space than a bonded pair
This means the lone pair is repelled more strongly than a bonded pair
Shapes from four electron pairs
Four electron pairs around the central atom repel eachother as far as possible into a tetrahedral arrnagement
Lone pairs decrease the bond angle between bonded pairs as they repel more strongly
No lone pairs - 109.5 (tetrahedral)
1 lone pair - 107 (triangular pyramid)
2 lone pairs - 104.5 (bent)
bond angle is reduced by 2.5 degrees for each lone pair
Shapes from multiple bonds
Each multiple bond is treated as a bonding region
CO2 - Four bonded pairs around the central carbon are arranges as two double bonds, so two bonded region
Three electron pairs - bond angle of 120 (trigonal planar)
Six electron pairs (octohedral) - bond angle of 90
Five electron pairs (Trigonal bipyramid)
Shapes of ions
Ammonium/ sulfate ions
Four bonded pairs surrounding the central nitrogen atom
Has the same tetrahedral shape and bond angles in a tetrahedral shape (109.5)
Carbone/ nitrogen ions
Three regions of electron density around central atom
Bond angle of 120 degrees
Electronegativity
For covalent molecules with the same elements, bonded electron pair is shared evenly
When bonded atoms are different elements
Nuclear charged are different
Atoms are different sizes
Shared pair of electrons may be close to one nucleus
The attraction of a bonded atoms for the pair of electrons in a covalent bond
Measuring it
Pauling scale
Nuclear charge increase across the periodic table, atomic radius decreases
Floruine is the most electronegative element
Bond polarity
Non polar bonds
Bonded electron pair is shared equally between bonded atoms
Bond is non polar when:
Bonded atoms are the same
Bonded atoms have the same/ similar electronegativity
Polar bonds
Bonded electron pair is shared unequally between bonded atoms
Bond is non polar when:
Bonded atoms are different
Bonded atoms have different electronegativity
Separation of opposite charges is called a dipole
Dipole in a polar covalent bond doesn't change and is called a permanent dipole
HCl
Chlorine has a higher electronegativity than Hydrogen
Chlorine atom has a greater attraction for the bonded pair of electrons
There is a small positive charge on the hydrogen, and a small negative charge on the chlorine
Water
Polar
Two O-H bons each have a permanent dipole
They don't exactly oppose eachother as they're in different directions
Overall, oxygen has a delta - charge and the hydrogen has a delta +
CO2
Non-polar
Two C=O bonds have a permanent dipole
Two dipoles act in opposte directions and exactly oppose one another
Dipoles cancel out, overall dipole is 0
Polar solvents and solubility
Water molcules attract Na+ and Cl- ions, the lattic breaks down
Na+ ions are attracted to the oxygen of water molecules
Cl- are attracted to the hydrogen of water molecules