Lecture 17
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What are Van der Waals’ forces?
weak interactions caused by momentary changes in electron density or distribution in non-polar compounds
What causes Van der Waals forces?
it results from the polarization of electrically neutral atoms or molecules that are not themselves polar
How do atoms feel electrical forces?
Every part of an atom or molecule feels an electrical force exerted on it by all parts of the other. This causes a temporary shift of the electron because of the presence of other electrical charges in the neighboring atoms
What is the result of Van der Waals Forces?
The sum of attractive forces wins out over repulsive forces adn weak bonds are formed
What happens because electrons are constantly in motion?
The electron density at any given instant may not be totally symmetrical across the atom
What does the difference in electron density give rise to?
a temporary dipole, even if the atom is non-polar itself, causing a temporary dipole in another molecule
How is graphite an example of van der Waals forces?
Because it is made of carbon, the carbon atoms within a single layer are strongly linked by covalent bonds, but are held together by much weaker Van der Waals bonds
Why are Graphite and Diamond, even though they are made of the same materials, two entirely different materials?
Graphite is in a plane, where weaker bonds exist between layers than within layers, but Diamonds have a 3-D framework and strong construction
All chemical reactions involve _______ in elements and compunds as well as ________ to form chemical bonds
rearrangement of the atoms, rearrangement of electrons
How are chemical reactions expressed?
reactants (on the left side) -> products (right-hand side)
What are redox reactions?
Reactions in which there is a simultaneous transfer of electrons from one chemical species to another (an atom or molecule)
Redox reactions consist of?
two half reactions (oxidation and reduction) which occur simultaneously. Neither oxidation nor reduction can take place without the other
What is the difference between oxidation and reduction?
Oxidation, loss of e- Reduction, gain of e-
What is the mnemonic device OIL RIG?
Oxidation Is Loss - Reduction Is Gain
In the compound NaCl, which is oxidized and which is reduced?
Na is oxidized as it looses an e- and Cl is reduced as it gains one
How would you write the redox reaction equation for NaCl?
Na^0 + Cl^0 –> Na^+1Cl^-1
What are the two half-reactions equations that happen simultaneously for NaCl?
Na^0 —> Na^1+ + e- Cl^0 + e- —-> Cl^1-
Besides the loss of an electron, how else can oxidation happen?
By gaining oxygen, as in the process of rusting
What are the two ways reduction happen by?
A gain of e- or the loss of oxygen
The transfer of ____ from the atom that is oxidized to the atom that is reduced can _____
electrons, be used to produce electricity
How is electricity created in oxidation and reduction pairs?
When they are kept apart the flow or electrons has to travel between them through some external pathway
Why do oxidation and reduction reactions happen at all?
Because each of the electrons possesses: Kinetic energy (its orbital motion around the nucleus), Chemical potential energy (position relative to the nucleus), and electro potential energy (electrical repulsion between electrons), where the total energy of the single electron is a sum of all of these energies (E). So energy of Na would be E x 11(atomic number of Na) or E_Na
After the formation of the ionic bond what happens?
The total force on each electron is now different, the total energy of each atom will be different, and the total energy of the system will be different
How are exothermic reactions created?
If E initial > E final