Chemistry: Chemical Bonds

Trying to catch up in my snails progress through various science and math resources.  Here's my review notes for a chemistry chapter on chemical bonds.

• The octet rule is the fact that (except for H and He), the outermost electron shell of Groups 1A-7A want to have eight electrons.
• For those in the outer groups, there will be a tendency to go into ions, so those on the right tend to become cations (positive ions) by losing electrons to end up with the 8 outer electrons of a lower shell.  Those on the left tend to gain electrons and become negatively charged anions to fill up the outermost shell they start with.
• Electronegativity is how strongly an atom holds on to its electrons.  It increases from left to right on the periodic table and from bottom to top in a column (as does ionization energy).
• An ionic bond forms with a difference in electronegativity of 1.9 or greater between two atoms.  A covalent bond forms if less than 1.9.  A non-polar covalent bond forms if the difference in electronegativity is below 0.5.
• In an ionic bond, electrons transfer from one atom to another (e.g., from Na to Cl).  In a covalent bond, two atoms share electrons (mostly elements toward the middle of the periodic table).  In a polar covalent bond (electronegativity between 0.5 and 1.9), electrons are shared but gravitate more toward one atom than another (the one more to the right and top in the table).  Such a polarized compound is called a dipole.
• An ion can be one type of element (monatomic, add -ide) to it (choride).  An ion can also be polyatomic.  To name a binary ionic compound, name the first (cation) element, then the second (anion).  "Ous" and "ic" (think ars-en-ic with a British accent) are the lower and higher charged ions of an element that can form more than one ion (e.g., Fe).
• A binary molecular compound will use di- tri- and so forth.
• VSEPR or Valence Shell Electron Pair Repulsion model predicts the structure of a compound.  An atom with 4 regions of electron density would be tetrahedral with default angles of 109.5 degrees.  Three regions would be pyramidal with a default of 120 degrees.  Two regions would be linear (180 degrees).

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.