atom - makes up all matter and all substances in the universe  

• can be seen indirectly w/ tech such as tunnel microscopy
• electrons - (-) charge; revolves around the nucleus
• neutrons - no charge; in the nucleus
• protons - (+) positive charge; in the nucleus; determines the atom's atomic number
• mass - amount of substance
• weight - force gravity exerts on a substance
• atomic mass - equal the combined mass of neutrons/protons; measured in daltons (6.02*10^23 daltons=1 gram)

isotopes - atoms of an element w/ different numbers of neutrons  

• elements - same atomic number, same chemical properties
• radioactive isotope - isotopes that decay due to unstable nuclei; decay is constant
• half-life - time is takes 1/2 of the atoms to decay; can be used to determine age of biological material
• released subatomic particles could cause mutations in genes

electrons - determines the charge in each atom  

• neutral atoms - not net charge, same number of electrons/protons
• ions - atoms in which the number of electrons is different from the number of protons
• cation - ion with positive charge
• anion - ion with negative charge

orbital - area where an electron is most likely to be found  

• each can't contain over 2 electrons
• electrons determine the atom's chemical behavior because the nuclei never interact
• electrons contain potential energy based on their position
• oxidation - loss of electron
• reduction - gain of electron
• energy level - based on an electron's distance from the nucleus; different from orbitals

periodic table - developed by Dmitri Mendeleev  

• elements' chemical properties repeated themselves in groups of 8
• valence electrons - electrons on the outermost energy level; basis for the atoms' chemical properties
• noble gases - elements w/ filled outer levels; are inert and nonreactive
• halogens - elements w/ 7 electrons in outer levels; extremely reactive
• octet rule - atoms tend to completely fill their outer levels

chemical bonds - connects atoms in a molecule and molecules in a compound  

• ionic bonds - forms between atoms of opposite charge; exists between an ion and all oppositely charged ions in the area
• covalent bonds - forms between 2 specific atoms when electrons are shared; has no net charge or free electrons
• single bond - 1 electron is shared
• double bond - 2 electrons are shared
• triple bond - 3 electrons are shared
• structural formulas - shows elements in a compound and their bonds
• molecular formulas - shows only the elements in a compound
• atoms can form many covalent bonds (ex. carbon)
• chemical reaction - forming/breaking of chemical bonds
• reactants - original molecules before the reaction
• products - resulting molecules after the reaction

factors influencing reactions  

• higher temperature increases reaction rate
• temperature must not be so high that it destroys molecules
• more reactants exposed to each other increases reaction rate
• catalyst - substance that increases reaction rate; proteins called enzymes act as catalysts in organisms