Any material all samples of which have the same composition and properties (a mixture is not a substance).
The smallest unit of an element that still retains the properties of that element. Contains 3 subatomic particles: (Protons, Neutrons, Electrons)
Carries a positive charge and are found in the nucleus of an atom. ( the atomic number in the nucleus.)
Are neutral and are also found in the nucleus. The number of electrons in an atom must equal the number of protons. To find the number of neutrons in an atom subtract the atomic number from the mass number in an element.
Carries a negative charge and are found outside the nucleus and arranged according th their energy level.
Atoms of the same element (with the same number of protons) that contain a different number of neutrons, (atoms of the same element that have different numbers of neutrons)
an ion that has a negative charge; forms when valence electrons are added to the outer energy level, giving the ion a stable electron configuration
an electron in the outer shell of an atom which can combine with other atoms to form molecules
one of the elements of Group 18 of the periodic table (helium, neon, argon, krypton, xenon, and radon); noble gases are unreactive
any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
An isotope that has an unstable nucleus and undergoes radioactive decay., An atom with normal number of neutrons that spontaneously breaks down releasing particles and energy