2.1 - Early Chemical Discoveries and the Atomic Theory
Law of conservation of mass - The total mass of substances present after a
chemical reaction is the asame as the total mass of substances before the
reaction. Matter is neither created nor destroyed in a chemical reaction.
Law of constant composition - All samples of a compound have the same
composition - the same proportions by mass of the consituent elements.
Dalton's atomic theory - the theory involves three assumptions:
- Each cemical element is composed of minute, indivisible particles called atoms.
Atoms can neither be created nor destroyed during a chemical change.
- All atoms of an element are alike in mass (weight) and other properties, but the
atoms of one element are different from those of all other elements.
- In each of their compounds, different elements combine in a simple numerical
ration, for example, one atom of A to one of B (AB), or one atom of A to two of B
Law of multiple proportions - If two elements form more than a single compound,
the masses of one element combined with a fixed mass of the second are in the
ratio of small whole numbers.
2.2 - Electrons and Other Discoveries in Atomic Physics
All matter is made up of positively or negatively charged particles.
Cathode rays - A type of radiation emitted by the negative terminal, or cathode.
Eventually became known as electrons.
Radioactivity - Continuous radiation of a material.
Alpha particles - Carry two fundamental units of positive charge and have
essentially the same mass as helium atoms. They are identical to He2+ ions.
Beta particles - Negatively charged particles produced by changes occurring
within the nuclei of radioactive atoms and have the same properties as electrons.
Gamma rays - (y), a form of radiation unaffected by electric or magnetic fields. It
is not made up of particles; it is electromagnetic radiation of extremely high
2.3 - The Nuclear Atom
Rutherford's explanation of alph