Lecture 5: Concentration Cells, The Periodic Table, and Properties of Light
When the concentrations are different electrons flow from the side with the less concentration solution (Anode) to the side with the more concentration solution.
The cell stops working when the concentration is equal
electrode salt electrode Platinum
- In a cell with different concentrations (same metals) the EMF is higher than when the concentrations are equal.
- In the normal cell - one metal gets oxidized, the other reduced (Driving force) Difference in Potential energy
- The difference in energy is due to the entropic difference in the solution - the more concentrated the solution the lower entropy than the less concentrated solution.
- Electrons will flow from the electron with less concentrated solution to the electrode in the more concentrated solution
- Oxidation of the electrode in the less concentrated solution will increase the ion concentration in the solution - less concentrated solution has the anode. (And opposite)
- The cell has the same half reaction in both cell compartment but with different concentrations of electrolytes.as long as the concentration of the solutions are different the cell potential is >0 and the cell can do work.
The Periodic Table - Atomic Radius, Ionization Energy and Electronegativity
All have the same number of Valence electron (outer shell)
- Atomic Radius as we go down the table, the atomic size increases. As we move to the right, atomic ratios decreases.
- Ionic Radius - Electrons repel each other, so adding an electron makes the atom larger. Removing an electron makes it smaller.
- Ionization Energy - Energy required to remove an electron from the atom (always the one in the outer most shell) The farther the electron from the nucleus, the easier it is to pull it away. On the Periodic table, opposite from the atomic radius.
- Successive Ionization energies (KJ/mol) the more electrons removed, the less stable the atom becomes.
- Electron Affinity - (Opposite of ionization of energy) How much an atom wants to gain an electron.
- Electronegativity - Ability of an atom to hold electrons tightly
- The energy required to remove an electron from an atom
- The less likely an atom gives up an electron, the more energy is required to take that electron away.
- Increases across a period
= Charge due to the nucleus
= Charge due to the electrons
- As we go across a period from left to right, electronegativity increases. As we have more protons in the nucleus, higher nucleus charge/force. The force which the nucleus pulls the electrons is higher. (Ratio of protons in nucleus and electrons in outer shell)
- Measured on a Pauling scale
- As we proceed from top to bottom of a group, the electronegativity decreases
- For noble gases, electronegativity is undefined
Increases from left to right across a period and decreases from top to bottom
Basic Parts of an Atom
Atom - The smallest particle of an element - Retains the characteristics of the element
Nucleus - Contains the protons (+) and Neutrons (neutral)
Electron Cloud - move outside the nucleus in orbitals
Proton - (+) Very small mass 1 a.mu
Neutron - Neutral 1a.m.u
Electron - a.m.u , In a high speed
Atomic Structure Meets the Periodic Table
Atomic number - number of protons in the nucleus
Electron Shell - Row in the Periodic Table
Shell 1 - 2 electrons
Shell 2 - 8 electrons
Shell 3 - 8 electrons
Shell 4 - 18 electrons
Shell 5 - 18 electrons
Shell 6 - 32 electrons...
Frequency, Wavelength and Speed of Light
Frequency - (V) How often a wave cycle passes a given point per sec.
Wave Length - ( ) The distance from one wave cycle to the next
As the wave length is smaller the Frequency increases.
Measuring Frequency - Frequency = (unit - ls) / (Hz)
Speed of Light - 300,000,000 m/s 3.00 10 meters/sec (c)
Wavelength of 1 m = Frequency of 3 10 ls
(each wave length has a corresponding Frequency)
Wavelength ( ) Frequency (V) = Speed of Light (Constant)
What is Light?
All electromagnetic radiation moves at the speed of light.
All waves move at a speed equal to wavelength Frequency
How is Electromagnetic Radiation Produced?
E = h V Quantum Revolution
h - Planks Constant
V - Frequency of Photon
Photo electric Effect, Work Function, Threshold Frequency, Wavelength, Speed and Kinetic Energy
Photo electric Effect
The energy carried by a photon can be transferred to an electron. When hitting a metal, there is enough Kinetic energy to escape and bounce of the metal. The frequency needs to be at a certain wave length to eject an electron from the surface of a certain metal. This doesn't change if the amount of light is added, only wave length matters, to get an electron to eject, If the wave length is high enough to eject an electron, then adding more light will increase the amount of electrons ejected. You just need to pass the threshold)
h - Planks Constant
- Threshold Frequency
- wave length
- Required to eject the e
Speed of the e
m - (kg)
V - Speed
Maximum Wave Lenth
- Work function (in J)
To see if the light can eject e