Chapter 6: Shapes of molecules & IMF Flashcards
Shapes, Electronegativity, Polarity, IMF, H-bonds
What is electron pair repulsion theory?
Electron pairs around a nucleus repel such that the structure of these pairs around the nucleus minimises repulsion.
By how much do lone pairs reduce bond angle?
2.5° for each lone pair around the nucleus
What are the 4 main types of shape with their corresponding number of electron dense regions.
Linear- 2
Trigonal Planar- 3
Tetrahedral- 4
Octahedral- 6
What are the bond angles of molecule shapes when there are no lone pairs?
Linear- 180°
Trigonal Planar- 120°
Tetrahedral- 109.5°
Octahedral- 90°
Do double or triple bonds affect bond angle?
No
Can electron pair repulsion theory be used on ions?
Yes
What is polarity?
When one nucleus out of a bonded pair exerts a greater attractive force on the bonding electrons such that a permanent dipole is produced.
What is electronegativity?
The attraction of a bonded atom for the pair of bonded electrons in a covalent bond.
How does electronegativity vary on the periodic table and why?
Increases across a period due to increased nuclear charge and reduced atomic radius,
Decrease down a group as atomic radius increase and shielding by electrons also increases.
How do you use electronegativity to determine a bond?
Evaluate the difference in electronegativity in bonded atoms:
0- Nonpolar
0 to 1.8- Polar
greater than 1.8- Ionic
What is a pure covalent bond?
A covalent bond where the bonding atoms are of the same element; hence diatomic molecules usually.
What is a nonpolar bond?
A bond where the electron pair is equally shared between each bonding atom.
What is polar bond
A bond where electronegativity differs such that the electron pair are not equally shared.
When is a molecule polar?
When a molecule contains polar bonds arrange asymmetrically such that they do not cancel.
What is a polar solvent?
A solvent which itself is polar and thus contains polar bonds.
What are the three types of intermolecular forces?
- Induced dipole-dipole interactions (London forces)
- Permanent dipole-dipole interactions
- Hydrogen bonding
What are induced dipole-dipole interactions (London Forces)?
Weak intermolecular forces which exist between all molecules. Caused by small fluctuations in the electron cloud around one molecule inducing an instantaneous dipole around neighboring molecules; radiating this effect out.
What are permanent dipole-dipole interactions?
A force arising from the electrostatic attraction of dipoles between polar molecules.
How do you increase the strength of London forces?
Greater attraction is felt by molecules with a greater number of electrons as the induced dipole becomes more significant (greater instantaneous polarity).
What is the structure of a solid molecule?
A simple Molecular Lattice.
What types of solvents pull polar and nonpolar molecules into solution?
Nonpolar solvents for nonpolar molecules
Polar solvent for polar molecules.
Why in solvents do like dissolve like?
As an intermolecular force needs to be overcome, induced dipoles and can overcome other induced dipoles but not permanent dipoles. Hence permanent can overcome permanent.
Can covalent molecules conduct?
No, no charge carriers.
What is hydrogen bonding?
A type of permanent dipole dipole interaction occurring between H-O H-N H-F. Where the polar hydrogen strongly attracts the lone pair around the O, N, F of other molecules.
Why is water anomalous?
Utilises hydrogen bonding to have a higher than expected boiling point and also has quite high surface tension.
Arrange the types of IMF in terms of strength smallest first.
- London Forces
- Permanent dipole dipole interactions
- Hydrogen bonding
