CHEMISTRY: ATOMS

atom

the smallest particle of an element

atomic mass

the average mass of all the isotopes of a element

atomic mass unit

a unit used to express atomic weight and is equal to 1/12 the mass of a carbon - 12 atom

atomic number

the number of protons in the nucleus of an atom

electron

a particle of matter with a negative charge

element

pure substances that cannot be broken down or decomposed into simpler substances by chemical means

isotope

forms of an element that the same protons but differing neutrons

mass number

the total number of protons and neutrons in the nucleus of an atom

neutron

particle that has no charge in the nucleus of an atom

nucleus

dense; positively charged central core of an atom

orbital

region in an atom in which an electrons are located

proton

particle with a positive charge

valence electrons

electrons on the outer level of an atom

wave - mechanical model

the current model of the atoms that deals with the wave - particle duality of nature