Week 3:  elements, atomic models, periodic table, isotopes

Elements: fundamental building block of all kinds of matter (solids, liquids, gases)

            examples:  oxygen, silicon, carbon, hydrogen, uranium, lead, sodium (about 100+ altogether)

      individual atoms “seen” (imaged) only recently, presence/existence was inferred for many years

 

Atomic Model:  elements often pictured as spheres but more like angry bees buzzing around hive

      hive = nucleus, contains 2 particles, represent almost all the mass of an atom, usually 50:50 ratio

            neutron:  massive particle in nucleus, has no electrical charge (neutral)

            proton:  massive particle in nucleus, has a positive (+ve) electrical charge

                  usually a neutron for every proton in the nucleus (but exceptions, see below)

      nucleus has an overall positive charge.  nucleus is very small compared to whole atom.

      particles in nucleus bound together with incredibly strong force, when you rupture nucleus = BANG

      angry bees = electrons, tiny particle, + massless, has a negative (-ve) electrical charge

            electrons swarm/orbit around nucleus forming electron cloud.  99.9% of atom = empty space

            electrons not tightly bound to atom, can be added or subtracted without too much effort

 

Problem:  moving charged particles produces electromagnetic waves (= radiation)

      example:  hook wire to battery, electrons move through wire, EM field/waves produced

            radiation produced means radiation/Energy lost, electrons should lose energy and stop…..

      Bohr:  at certain special distances out from the nucleus, electrons can orbit without losing energy

                  cannot circle/orbit nucleus at any old distance, must be at special distances from nucleus

                              special distances called orbitals or electron shells or energy levels

                              Why/how possible?  take chemistry and physics to learn about quantum mechanics

            lowest energy level closest to nucleus, highest energy levels farther away

                  when electron drops from high E shell to lower E shell, radiation emitted (called photon)

                              examples:  glow in the dark materials, fires, etc. all emitting photons

                  to push electron from low E shell to high E shell, must add/absorb photon/radiation

 

Periodic Table:  one way of arranging the different elements.   

      A) either 1 or 2 letter abbreviation for each element, first letter capitalized

            ex:  H = hydrogen, He = helium, S = sulfur, Si = Silicon, Fe = iron, K = potassium, etc.

      B) arranged by  atomic number above element.  atomic number = # of protons in nucleus

                  example:  silicon (Si) has 14 protons in its nucleus (that’s how silicon is defined)

            H = hydrogen = 1 = lightest element, 103 = Lr = Lawrencium = heaviest element

      C) average atomic mass given below the element: average number of protons and neutrons

            should be twice the atomic number (for every proton in atomic number, should be neutron). 

                  examples:  silicon, 2 x 14 = 28, actually 28.1.  oxygen, 2 x 8 = 16, actually 15.99

            these examples tell you that elements can have extra or missing neutrons = different flavors

                  different flavors of elements called isotopes.  some isotopes stable, others unstable

                  ex:  Carbon 14 (6 protons and 8 neutrons) is unstable = radioactive, will break down

                              Carbon 14 breaks down/decays into Carbon 12 (6 and 6) which is stable.

                  radioactive decay:  change from unstable to stable isotope, releases radiation and particles

return to top of page

-30-