The identity of the atom is determined by the # of protons in the nucleus. One can change one kind of atom into another by changing the number of protons in the nucleus These changes involve enormous amounts of energy. This is the source of nuclear energy and the atomic bomb. Most of these reactions result from nuclear decay and involve changes of only one or two protons in the nucleus.

Can we turn copper into gold? On a Periodic Table the Atomic Number also tells us the number of protons in the nucleus. Copper has 29 protons in its nucleus. Gold has 79 protons in its nucleus Clearly we can’t really turn copper into gold Alchemists didn’t really have a prayer to actually convert a “base metal” into gold either.

Most chemical reactions occur from interactions of the electrons. A neutral atom has the same number of electrons as protons. However, an atom can gain and lose electrons fairly easily to form ions, which can have positive or negative charge. Electrons are also responsible for the forces (bonds) which hold atoms together in a molecule.

The majority of chemical reactions can be classified as one of two kind of major reaction types. Acid/Base Reactions Oxidation/Reduction (Redox) Reactions.

The Proton The hydrogen atom has a mass of about 1 amu, as its nucleus contains only one proton and no neutrons. So the hydrogen atom without its electron has a charge of +1 and can be called a hydrogen ion, or more commonly a proton.

Acid Base Reactions In an Acid Base reaction, the hydrogen ion is simply transferred from one molecule or ion to another molecule or ion. Any examples?

This afternoon’s examples AcOH + HCO3-  AcO- + H2CO3 H2CO3  CO2 + H2O This reaction is reversible so it is also true that CO2 + H2O H2CO3  H+ + HCO3- 2AcOH + CaCO3 Ca(AcO)2 + H2CO3

Oxidation-Reduction Reactions In a Redox reaction electrons are transferred from one atom, ion or molecule to another atom, ion or molecule. This is the reaction we will use to turn the copper penny into “silver”, or more accurately coat the penny with zinc.

How does this happen? Zn(s) + 4-OH  ZnO22- + 2 H2O + 2e- 2H2O + 2e-  H2(g) + 2OH- Zn(s) + 2OH-  H2(g) + ZnO22- 2H2O + ZnO2- Zn2+ + 4OH- Zn2+ + 2e-  Zn(s) 2OH- + H2  2H2O + 2e- 2OH- + H2 + Zn2+  Zn(s) + 2H2O

Silver Penny to Gold This process is neither acid/base nor redox. In this reaction we form an alloy, i.e. a metal mixture. When we heat the zinc coated penny, the zinc atoms mix with the copper atoms to form brass, which has a gold-like color. We can use colorless nail polish to prevent tarnishing. Real gold does not tarnish.

What do we mean by tarnish? When a metal tarnishes, it is getting oxidized by O2 to a metal oxide. e.g. 4Ag + O2  2 Ag2O 2Zn + O2  2ZnO 2Cu + O2  2CuO Most metals, like these oxidize easily and form a smooth layer of oxides on the surface of the metal that actually protects it from further oxidation.

Iron doesn’t tarnish, it rusts and corrodes 4 Fe + 3O2  2 Fe2O3 (rust) The difference here is that rust does not form a smooth surface on Iron, it flakes off, exposes more metal surface to oxidation. We call this corrosion.

How is this a redox reaction? 4 Fe + 3O2  2 Fe2O3 (rust) 4 Fe  4Fe3+ + 12e- iron gets oxidized 3O2 + 12e-  6”O2-” oxygen gets reduced 4Fe3+ + 6O2-  2 Fe2O3

How does acid rain affect this? Iron needs water to get oxidized by air(O2). The water allows ions to move around, which is necessary for iron to corrode. Iron will not rust in anaerobic water. Iron will not rust in anhydrous air. Salt or acid, increase the rate of the redox process.

Creating Acid Rain Real acid rain is caused by the reaction of water with Nitrogen and sulfur oxides formed from car exhaust and industrial waste. e.g. SO3 + H2O  H2SO4(sulfuric acid!)

Making acid rain We will make “fake” acid rain, by first generating CO2, then bubbling it into water. AcOH + HCO3-  AcO- + H2CO3 H2CO3  CO2 + H2O This reaction is reversible so it is also true that CO2 + H2O H2CO3  H+ + HCO3-