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the smallest particle into which an element can be divided and still be the same substance. positive portion- small, massive, dense. Neutral.


a pure substance that cannot be separated or broken down into simple substances by physical or chemical means.


the tiny, extremely dense, positively charged region in the center of an atom. made up of protons and neutrons.


the negatively charged particles found in all atoms. electrons are involved in the formation of chemical bonds. they move in energy levels. 0 amu.


the positively charged particles of the nucleus. the number of protons in a nucleus is the atomic number that determines the identity of an element. 1amu.


the particles of the nucleus that have no charge. 1amu.

atomic mass

the weighted average of the masses of all the naturally occurring isotopes of an element.

atomic number

the number of protons in the nucleus of an atom.

atomic mass unit

the SI unit used to express the masses of particles in atoms.

mass number

the sum of the protons and neutrons in an atom.

electron clouds

the regions inside an atom where electrons are likely to be found.

energy level

the energy characteristic of a stationary state of a physical system.


charged particles that form during chemical changes when one or more valence electrons transfer from one atom to another.


atoms that have the same number of protons but have different numbers of neutrons.

periodic table

a highly organized chart listing all the known elements arranged in horizontal rows called periods and vertical columns called groups.


the quality or state of being periodic. Recurrence at regular intervals.


a horizontal row of elements on the periodic table.


a column of elements on the periodic table.


elements that are shiny and are good conductors of thermal energy and electric current. Most metals are malleable and ductile.


elements that are dull and are poor conductors of thermal energy and electric current.


elements that have properties of both metals and nonmetals. Sometimes referred to as semiconductors.

alkali metals

the elements in group 1 of the periodic table. They are the most reactive metals. Their atoms have one electron in their outer level.

alkaline earth metals

the elements in group 2 of the periodic table. They are reactive metals but are less reactive then alkali metals. Their atoms have 2 electrons in their outer level.

transition metals

the elements of groups 3 through 12.


the elements in group 17 of the periodic table. They are very reactive nonmetals, and their atoms have 7 electrons in their outer level.

noble gases

the unreactive elements in group 18 of the periodic table. Their atoms have 8 electrons in their outer level. (except for helium, it has 2 electrons)

carbon group

group 14. Carbon, silicon, germanium, tin, and lead. 4 electrons in the outer level.

nitrogen group

group 15. Nitrogen, phosphorus, arsenic, antimony, and bismuth. 5 electrons in the outer level.

oxygen group

group 16. Oxygen, sulfur, selenium, tellurium, and polonium. 6 electrons in the outer level. Reactive.

boron group

group 13. Boron, aluminum, gallium, indium, and thallium. 3 electrons in the outer level. Reactive.

stepped leader

From cloud to ground, usually faint, invisible - negative charge.


positive charges coming up from the ground. not visible to the human eye.

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