Chapter 6 Flashcards
How do electron pairs around central atom determine the shape
Electrons repel so they are arranged as far apart as possible to minimise repulsion and have a definite shape
3d shape of compound
What does solid line mean
Bond on the plane of paper
3d shape of compound
What does a solid wedge mean
Bond comes out of the plane of paper
3d shape of compound
What does a dotted wedge mean
Bond goes into plane of paper
Why does lone pair repel more strongly than bonded pair
Slightly closer to central atom and occupies more space
Which repels more: bonded and lone or bonding and bonding?
Bonded and lone repels most
How much is the angle decreased for each lone pair in compound
2.5 degrees
Shape and angle of H2
Linear
180 degrees
Shape and angle of CO2
Linear
180 degrees
Shape and angle of BF3
Trigonal planar
120 degrees
Shape and angle of CH4
Tetrahedral
109.5 degrees
Shape and angle of PCl5
Trigonal bipyramid
90 and 120 degrees
Shape and angle of SF6
Octahedral
90 degrees
Shape and angle of H3O +
Pyramidal
107 degrees
Shape and angle of H2O
Non linear
104.5 degrees
What is electronegativity
Amount of attraction of a bonded atom for the pair of electrons in a covalent bond
What is a pure covalent bond and example
H2
Equal electronegativity so electrons shared equally in bond
Why does electronegativity change
Factors that affect it is…
Nuclear charge are different meaning number of proton
Different size of atom so larger the size weaker attraction to outer shell where there will be a bond
Which atom would the shared electrons be closer to in HCl
Cl is more electronegative
Cl
Where does electronegativity increase according to Pauling scale in periodic table
Increases up the table
Increases from left to right of table so across
What is the meaning of non polar bond
Pair shared equally between bonded atoms that have similar or same electronegativities
What is a dipole
What does it mean by Cl end having a delta negative in HCl
It is a separation of opposite equal charges
Small partial negative charge
What is a permanent dipole
Dipole in polar covalent bond does not change
What is a polar molecule
Molecule with permanent dipoles and the shape is not symmetrical so the charges don’t cancel out
And there is an overall dipole
CO2 has permanent dipoles but it is classified as non polar
Why
Shape is symmetrical so dipoles cancel each other out
What shapes are symmetrical
4 points
Linear
Trigonal planar
Tetrahedral
Octahedral
How do polar compounds dissolve in water
Water surrounds lattice
Positive ion or delta positive attracted to O part of water
Negative part attracted to H
This attraction pulls and breaks the lattice and dissolves
Finish
Greater the difference in electronegativity the …. The permanent dipole
Greater
What are the three types of intermolecular forces
Induced dipole dipole interactions (London forces)
Permanent dipole dipole interaction
Hydrogen bond
What are the van der waals forces
Induced dipole dipole interactions (London forces)
Permanent dipole dipole interaction
What type of molecules do London forces work
All molecules
Polar and non-polar
How are London forces made
Fluctuations of electrons produce a changing dipole in molecule and at any moment an instantaneous dipole will exist temporarily.
This instantaneous dipole induces neighbouring molecules
And then there will be small attractions for an instant
How does number of electrons affect induced dipoles
More electrons mean larger instantaneous and induced dipoles, greater the induced dipole dipole interactions and stronger attractive force between molecules
What type of molecule do permanent dipole dipole interactions occur
Between different polar molecules
Which usually has a higher mp/bp
Polar or non polar?
Why?
Polar as it has both permanent and induced interactions
Non polar only has induced interactions so more intermolecular forces and more energy required to break all of this.
When does hydrogen bonding occur? What is it?
What atoms must or can be present?
Strong dipole dipole interaction between an electron deficient H atom and a lone pair of electrons on a highly electronegative atom on a different molecule.
H atom and (O, N, F)
Ice is less dense than liquid water
Why?
Hydrogen bonds holds water molecules apart forming an open lattice structure of ice
Features of water that are unusual compared to other similar molecules (because of H bonds)
2 points
High mp/bp as H bonds along with other intermolecular forces must be broken and require more energy
H bonds give water high surface tension and viscosity as H bonds pull molecules together (attractive force)
