the positively charged center of an atom, which contains protons and neutrons and has almost all the mass of the entire atom but only a tiny fraction of the volume.
isotope
a form of an element having a particular number of neutrons in the nuclei of its atoms. different isotopes of a particular element have the same atomic number but different atomic mass numbers.
brownian motion
the perpetual random movement of microscopic particles suspended in a fluid medium.
atom
the smallest particle of an element that can be identified with that element. consists of protons and neutrons in a nucleus surrounded by electrons
ion
an atom (or group of atoms bound together) with a net electric charge, which is due to the loss or gain of electrons.
nucleons
the principle building block of the nucleus; a neutron or a proton.
shell model of the atom
a model in which the electrons of an atom are pictured as grouped in concentric shells around the nucleus.
chemical formula
a description that uses numbers and symbols of elements to describe the proportions of elements in a compound or reaction.
protons
a positively charged particle that is one of the two kinds of particles found in the nucleus of an atom
compound
a chemical substance made of atoms of two or more different elements combined in a fixed proportion
