Chemistry: Atoms

This is to record for review a summary of my pilgrimage through a chapter of Chemistry:

• element, compound, mixtures homogeneous and heterogeneous...
• Dalton's early 1800 revival of atomism--law of conservation of mass and law of constant composition. Dmitri Mendelev in the 1800s developed the Periodic Table.
• mass number includes both protons and neutrons, atomic number just protons
• Isotopes have differing numbers of neutrons in a particular atom.  Atomic weight is the average mass of a particular atom, with 1 amu (atomic mass unit) being the mass of a proton (1.666 x 10^-24g).
• The 18 non-metals are on the right side of the Periodic Table (except for Hydrogen).  They all conduct electricity except for graphite.
• 6 elements are metalloid: boron, silicon, germanium, arsenic, antimony, and tellurium.  The rest are metals.
• Groups are vertical columns.  Halogens are Group 7.  Alkali metals (except for Hydrogen) are Group 1.  Noble gases are Group 8.  Periods are horizontal rows. 
• The principal energy levels are numbered, 1, 2, 3, 4...
• These "shells" also have potential subshells: s, p, d, and f.  Electrons in subshells are paired, but only when all the potential orbitals have at least one electron.  The s subshell only takes 2 electrons.  The p subshell takes up to 6 (3 orbitals).  The d takes 10 (5 orbitals) and f takes 14 (7).  s shells are spherical. p shells are like bar bells along an imaginary x, y, and z axis.
• The transition elements are in between the main group elements columns 2 and 3.  They include the d shell.  The inner transition metals are the f shell and are located in the 6th and 7th periods before the normal transition metals.
• The valence shell is the outermost shell and its electrons are valence electrons.  The Lewis-dot structure is very helpful in processing how atoms bond on the basis of their outermost shell.
• Ionization energy, the propensity of an atom to form an ion (to gain or lose electrons in the valence shell), increases as you move up and to the right of the Periodic Table.