Lecture 2 - Chemical Interactions Flashcards
What are the different types of bonds?
Covalent
Noncovalent –> Hydrogen, Ionic, Van der Waal’s, hydrophobic
Describe the covalent bond
intramolecular
sharing of electrons
Strong and stable
caused by overlap of atomic orbitals
Define bond energy
Amount of energy required to break a bond, or the amount of energy released when the bond is formed
Why are weak chemical interactions strong?
They are very weak bonds individually, and require much less energy to break. They are very transient/dynamic, constantly forming and reforming, but because there are so many of them, it is very unlikely that all of the bonds will be broken at the same time, so the molecule is stable
Describe hydrogen bonding
the interaction between a covalently bound hydrogen on a donor group and a pair of non-bonded electrons on an acceptor group
Requires a hydrogen bond donor and a hydrogen bond acceptor
Approximately 3 A long
Strongest noncovalent interaction
Describe hydrogen bonding in water
Because water has unequal sharing of electrons, there are partial charges on the hydrogens, and oxygen has a pair of lone electrons. Each H2O can H bond to 4 other H2O molecules, accounting for the high melting/boiling point of water
Why does water make a good solvent?
Polarity of water means it interacts well with polar/ionic solutes. Forms hydration shells around the ions
What is the dielectric constant?
Measure of a solvent’s ability to decrease the electrostatic attraction between ions relative to a vacuum
Describe ionic bonding
due to electrostatic interactions between opposing charges
Coulomb’s law describes force of attraction
Describe Van der Waal’s forces
All intermolecular forces between electrically neutral molecules
Constantly forming and breaking, cumulative # imparts stability
What are the three types of dipole interactions, and describe them
1) Permanent dipoles –> covalent bonding between polar groups
2) Dipole-induced dipoles –> permanent dipole induces a dipole in a neighbouring group
3) London Dispersion forces –> nonpolar groups polarize electrons in a neighbouring group due to random fluctuations creating transient dipoles
Describe hydrophobic interactions
Because water is forced into clathrates around non-polar molecules, which are hydrophobic, the grouping of these nonpolar molecules means that there is less total surface area requiring highly-ordered water molecules. Therefore, grouping means an increase in entropy of the system, even though it is decreasing the entropy of the molecules
Describe the difference between covalent and dipole-dipole interactions
Covalent bonding is the sharing of electrons to fill a valence shell. Polar covalent is where there is unequal sharing of the electrons. Dipole-dipole interactions refer to intermolecular bonding, where there is a dipole moment. The delta positive side interacts with a delta negative side.
Covalent bonding is INTRAMOLECULAR, dipole-dipole is INTERMOLECULAR
