subatomic particles - determine the atom's characteristics  

• electronic charge - 1.602*10-19 coulombs
• atoms have the same number of protons/electrons, no net charge
• atomic mass unit (amu) - used to measure atomic mass; equal to 1.66054 x 10-24 grams, 1/12 the mass of a carbon-12 atom
• angstrom - 10-10 meters; along w/ picometers, used to express atomic diameters;
• atomic diameter equal to about 1-5 angstroms, atomic nuclei equal to about 10^-4 angstroms
• interiors of collapsed stars may approach the density within atomic nuclei

basic forces - 4 basic interactions in nature  

• gravity - attraction between all objects in proportion to their masses; incredibly small between atoms
• electromagnetism - forces between electrically charged objects
• strong nuclear force - acts between subatomic particles in the nucleus to keep them together
• weak nuclear force - weaker than electrical forces, but stronger than gravity; shows up in certain types of radioactivity

isotope - elements that differ in number of neutrons  

• atomic number - number of protons
• atomic mass - number of protons/neutrons
• nuclide - atom of a specific isotope
• average atomic mass - found by using the masses of all its isotopes and their relative abundance; aka atomic weight

periodic table - developed in 1869  

• similar elements placed in the same column (group)
• chemical/physical properties show repetition
• metallic elements - on the left/middle part of the periodic table; shiny, malleable, conductors
• nonmetallic elements - separated from metals on the table by a diagonal line from boron to astatine; brittle, dissolves to form salt, insulators
• metalloids - elements that have properties falling between metals/nonmentals; shiny/brittle
• 8A - unreactive, inert/noble gases; no charge
• 1A - alkali metals; +1 charge
• 2A - alkaline earth metals; +2 charge
• 6A - chalcogens; -2 charge
• 7A - halogens; -1 charge