classification of matter

MATTER

anything that occupies space and has mass.

PURE SUBSTANCES

fixed composition; cannot be further purified.
HOMOGENEOUS MATTER
uniform composite throughout.
HETEROGENEOUS MATTER
nonuniform composition.
MIXTURES
a combination of two or more pure substances.
COMPOUNDS
elements united in fixed ratios.
ELEMENTS
cannot be subdivided by chemical or physical means.
ATOM
the smallest unit of an element that has all of the properties of an element.

MASS NUMBER

the sum of the number of protons plus neutrons in the nucleus of an atom.
ATOMIC NUMBER
the number of protos in the nucleus of an atom.

ISOTOPES

atoms with the same number of protons but a different number of neutrons.
ATOMIC MASS
the weighted average of the masses in amu of the isotopes of an element found in nature.
VALENCE SHELL
the outermost incomplete shell.
VALENCE ELECTRON
an electron in the valence shell.
OCTET RULE
atoms and ions are the most stable when they have EIGHT electrons in the valence shell.

ANIONS

negatively charged ions.
CATIONS
positevly charged ions.
COVALENT BOND
bond formed as a result of sharing aa pair of electrons.