All pure substances are made of atoms. All substances can be divided but not “ad infinitum” (forever) Atoms are the smallest part that cannot be divided.

 Atoms of one element are different from atoms of another element.  However atoms of one element are identical to other atoms of the same element.  Atoms combine in simple, whole number ratios to form compounds.  Compounds themselves have a unique composition.  Chemical reactions occur when atoms are joined, separated, or rearranged.

 Cathode Ray Experiment  Investigate the relationship between the cathode ray (electric flow) and electric charge.  This helped bridge the gap between matter and energy.  Just as importantly, the work led to the “discovery” of the subatomic particle called the electron.

Cathode ray experiment set-up.

Dough = positive mass Chips = electrons

He conducted the Gold Foil Experiment An atom was considered a solid beam of alpha particles Most particles passed straight through, some bounced back But others scattered at 90 o to the foil  Impossible for solid objects!

Alpha particles:  Most pass through some empty space  Some come close to a positively charged, extremely small, solid nucleus and are deflected Electrons must be located in the empty space!

All electrons are at the same distance from the nucleus

 Electrons are held in quantized (energy specific) shells  If an atom gains energy, the electrons may move up shells.  When atom lose energy the electron moves back to or toward it’s ground state and releases the energy in the form of EMR (bright line spectrum).

Bohr’s Planetary model.. If the nucleus were made the size of a marble, the closest electron to the nucleus would be more than 120 yards away.

Progression of atomic theory; one builds from the others in the past.

What is the difference?

 Isotope - atoms with the same number of protons (same element) but with different numbers of neutrons (different mass)  Ion - an atom or group of atoms that has a positive or negative charge

 By gaining or losing electrons

 Atoms or groups of atoms that have a positive or negative charge  Formed by gaining or losing electrons  Ions are NEVER formed by gaining or losing protons

 Positive charge  Formed by the atom losing electrons  Metals form cations

Ca Ca e -

 Negative charge  Formed by the atom gaining electrons  Nonmetals form anions

O + 2e - O -2

 Use the periodic table  Columns are called groups or families ◦ The elements in the same group tend to have the same chemical properties ◦ Groups are referred to by the number over the column

The previous images display some of our hopes and fears associated with nuclear radiation. We know the images, and some of the uses, but what is “Nuclear Radiation” and where does “it” come from?

 In nuclear chemistry, an atom is referred to as a nuclide.  It is identified by the number of protons and neutrons in the nucleus.  Examples:  or Uranium-238

+ + + There are 2 forces at work  The repulsive force & a strong nuclear force.  A strong nuclear charge set up by the neutrons

 Alpha radiation (the alpha particle -  ) is composed of 2 protons and 2 neutrons that have been ejected from an unstable nucleus.  Alpha particles have the composition of the Helium-4 nucleus, but do not posses electrons.

In the above illustration, the plutonium-239 nucleus undergoes alpha decay to form the uranium-235 nucleus and the ejection of the alpha particle.

Uranium – 235 undergoes alpha decay.

 Beta radiation (the beta particle-  ) is formed when a neutron within an unstable nucleus decays to form a proton and an electron. (Too many neutrons)  The newly formed electron is ejected from the nucleus/atom. The high speed electron is the beta particle.

In the above diagram, the carbon-14 isotope undergoes beta decay to form the nitrogen- 14 isotope and eject a beta particle.

Potassium-40 undergoes beta decay. Give the nuclear equation for this decay process.

 Unlike the other forms of nuclear radiation, gamma radiation (  ) is in the form of an electromagnetic wave (EMR).  Gamma radiation is emitted from an unstable nucleus as the nucleus undergoes some rearrangement process (Alpha decay).

 In a nuclear fission reaction, a large nucleus is split into two smaller nuclei of approximately equal mass  Fission reactions are used to provide what is commonly called nuclear power.

 One fission reaction produces enough neutrons to start 3 more fission reactions, which in turn produces the neutrons needed to start 3 more reactions, and so on, in a series called a nuclear chain reaction.

Nuclear Fusion  In a nuclear fusion reaction, 2 small nuclei join to form a larger nucleus.

 Fusion reactions are hard to produce and to control  So far it takes a tremendous amount of heat to start  Cold fusion is a natural research opportunity, – The goal is to harness the power of the sun

 Every radioactive isotope has a unique rate of decay or half-life – 1 half life is the time required for ½ of nuclei of a radioactive sample to decay – After 1 half-life, ½ of the original nuclei have undergone transmutation  Half lives may be as short as a fraction of a second or as long as billions of years

 The half life of a substance is 2 minutes. How much will be left if you start with 10 grams after 10 minutes?