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The study of matter


Substance that has mass and occupies space. Made up of atoms.


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.


Identified by its symbol and it's atomic number.

Atomic Number

Is equal to the number of protons found in the nucleus of each of its atoms.

Mass Number

The number of protons + neutrons found in the nucleus of an atom.


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)

Atomic Mass

total mass of the protons and neutrons in an atom, measured in atomic mass units


atom that has a positive or negative charge


an ion with a positive charge produced by the loss of one or more electrons


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

Valence electron

an electron in the outer shell of an atom which can combine with other atoms to form molecules


an element that has some characteristics of metals and some characteristics of nonmetals

Noble Gas

one of the elements of Group 18 of the periodic table (helium, neon, argon, krypton, xenon, and radon); noble gases are unreactive


a horizontal row of elements in the periodic table


(chemistry) two or more atoms bound together as a single unit and forming part of a molecule


any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.

Radio isotope

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


a chemical element lacking typical metallic properties., an element that conducts heat and electricity poorly.

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