molecules
when 2 or more atoms are joined together in specific shapes
states of matter
the 3 forms that matter can assume: solid, liquid & gas
gas
matter that has no fixed volume or shape; it conforms to the volume & shape of its container
liquid
matter that has a distinct volume but no specific shape
solid
matter that has both a definite shape & definite volume
pure substance
matter that has a fixed composition & distinct properties
elements
a substance consisting of atoms of the same atomic number. Historically defined as a substance that cannot be separated into simpler substances by chemical means.
compounds
a substance composed of two or more elements united chemically in definite proportions
mixtures
a combination of 2 or more substances in which each substance retains its own chemical identity
law of constant composition
states that the elemental composition of a pure compound is always the same, regardless of its source (law of definite proportion)
physical properties
can be observed without changing the identity & composition of the substance. includes color odor, density, melting & boiling point & hardness
chemical properties
describe the way a substance may change or react, to form other substances: common chemical property is flammability (ability of a substance to burn in the presence of oxygen)
intensive properties
properties like temperature & melting point that do not depend on the amount of sample being examined & are particularly useful in chemistry because many intensive properties can be used to identify substance
extensive properties
depend on the amount of sample, with 2 examples being mass & volume. they relate to the amount of substance present
physical change
substance changes its physical appearance, but not its composition (example water)
changes of state
example: from liquid to gas or from liquid to solid-all are physical changes
chemical change (chemical reaction)
a substance is transformed into a chemically different substance (example hydrogen burns in air because it undergoes a chemical change because it combines w. /oxygen to form water
precision
how close the measurements are to each other
accuracy
how close your measured answer is to the accepted answer