Chapter 6 Flashcards
What is the electron-pair repulsion theory?
Electron pairs around a central atom determine the shape of the molecule/ion.
Electron pairs repel to be as far apart as possible, the arrangement therefore minimises repulsion.
What does the solid line show?
A bond in the plane of the paper
What does the solid wedge show?
A bond that comes out of the plane of the paper
What does the dotted wedge show?
A bond that goes into the plane of the paper
Why do lone pairs repel more strongly then bonded pairs?
A lone pair of electrons is slightly closes to the central atom and occupies more space.
By how much does a lone pair reduce a bond angle?
2.5 degrees
What is a tetrahedral shape like?
4 bonded pairs, 0 lone pairs
2 solid lines next to each other, 1 dotted wedge and one solid wedge.
109.5 degrees
What is a pyramidal shape like?
3 bonded pairs, 1 lone pair
1 of each, solid/dashed/line
107 degrees
What is a non-linear shape like?
2 bonded pairs, 2 lone pairs.
1 straight line and one solid wedge.
104.5 degrees
What is a linear shape like?
2 electron pairs, O lone pairs
2 double bonds
180 degrees
What is a trigonal planar shape like?
3 electron pairs, 0 lone pairs
3 straight lines
120 degrees
What is an octahedral shape like?
6 electron pairs, 0 lone pairs.
2 of each type of line/wedge. the solid wedges at bottom left and right, dotted at top left and right, straight lines at top and bottom.
90 degrees
What is electronegativity?
The attraction of a bonded atom for the pair of electrons in a covalent bond.
The shared pair of electrons may experience more attraction from one of the bonded atoms than the other.
How is electronegativity measured?
The Pauling scale is used.
In which direction does the electronegativity values increase?
Across and up (the most electronegative is Florine)
What is the bond type if the electronegativity difference is 0?
Covalent
What is the bond type if the electronegativity difference is 0-1.8?
Polar covalent
What is the bond type if the electronegativity difference is greater then 1.8?
ionic
How is the bonded electron pair shared in a non-polar bond?
Its shared equally between the bonded atoms.
This normally occur when the bonded atoms are the same eg H-H
How is the bonded electron pair shared in a polar bond?
Its shared unequally between the bonded atoms.
Polar bonds occur when there is a difference in electronegativity values between atoms.
Is the more electronegative atom going to have a delta positive or negative charge?
Delta negative
What is a dipole?
The separation of two opposite charges
What is a permanent dipole?
A dipole in a polar covalent bond that doesn’t change.
How is a molecule polar when there is electronegativity difference?
H2O is polar. Both of the O-H bonds have a permanent dipole and act in different directions, they dont oppose each other so the dipoles dont cancel out.
How is a molecule non-polar when there is electronegativity difference?
CO2 is non-polar. Despite them each having a permanent dipole, they act in opposite directions so the dipoles cancel
C=O
What are intermolecular forces?
Weak interactions between dipole of different molecules.
What are the 3 types of intermolecular forces?
-London forces (induced dipole-dipole interactions)
-permanent dipole-dipole interactions
-hydrogen bonding
What are intermolecular forces responsible for?
physical properties like melting/boiling points.
What are London forces?
Weak intermolecular forces between all molecules, the movement of electrons produces a changing dipole in a molecule. At any instant an instantaneous dipole will exist and this induces a dipole on a neighbouring molecule which then induces further dipoles on neighbouring molecules. So they all attract one another.
How does a molecule having more electrons impact its London forces?
- larger the instantaneous and induced dipoles
- greater the induced dipole-dipole interactions
- Stronger attractive forces between molecules
so they have larger boiling points since more energy is needed to overcome the intermolecular forces.
What is a simple molecular substance?
Made up of simple molecules (small units with a definite number of atoms with a definite molecular formula).
What is the structure of a simple molecular substance?
Simple molecular lattice. They are held in place by weak intermolecular forces. But the atoms in the molecules are bonded together strongly by covalent bonds.
Describe the melting/boiling point of a simple molecular substance?
Weak intermolecular forces are broken with not much energy, they are weak. So simple molecular substances have low mp/bp.
But only the weak intermolecular forces holding the lattice together break, not the strong covalent bonds between atoms.
Describe the solubility of a simple molecular substance? (NON-POLAR ADDED TO POLAR)
When a non-polar simple molecular substance is added to a polar solvent there is little interaction between the molecules in the lattice and the solvent molecules. So the intermolecular bonding in the polar solvent is too strong to be broken.
So non-polar simple molecular substances are insoluble in polar solvents.
Describe the solubility of a simple molecular substance? (NON-POLAR ADDED TO NON-POLAR)
When a simple molecular compound is added to a non-polar solvent intermolecular forces form between them.
The interactions weaken the intermolecular forces in the simple molecular lattice so they break and the compound dissolves.
So non-polar simple molecular substances are soluble in non polar substances.
Describe the solubility of a simple molecular substance? (Polar added to polar)
The polar molecules attract each other so they dissolve. The solubility depends on the strength of the dipole.
Describe the electrical conductivity of a simple molecular substance?
There are no mobile charged particles in simple molecular structures so there is nothing to complete an electrical circuit.
Therefore simple molecular structures are non-conductors of electricity.
What is a hydrogen bond?
Permanent dipole-dipole integration between molecules with an electronegative atom with a lone pair of electrons or a hydrogen atom.
It acts between a lone pair of electrons on an electronegative atom in one molecule and a hydrogen atom in a different molecule
