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is a pure substance that cannot be broken down into simpler substances by a chemical reaction.


located on the left side of the periodic table and include 2 transition rows at the bottom. They are shiny solids that are good conductors of heat and electricity. All of them are solids at room temperature except for mercury, which is liquid.


do not have a shiny appearance, and they are generally poor conductors of electricity. They like sulfur and carbon are solids at room temperature.


have properties intermediate between metals and nonmetals. Only seven elements are categorized as this kind of element.


the number of naturally occurring elements


the number of elements prepared by scientists in the laboratory


total number of elements currently known

oxygen, carbon, hydrogen and nitrogen

Comprise 96% of the mass of the human body and are known as the building block elements


needed for hemoglobin


a protein that carries oxygen in red blood cells


the protein that stores oxygen in muscle


needed for proper functioning of many enzymes in liver and kidneys


needed for proper thyroid function

Major Minerals

present in body fluids (K, Na, Cl)

Magnesium (Mg) and Sulfur (S)

elements found in proteins

Calcium (Ca) and Phosphorus (P)

present in teeth and bones

100 mg

amount of each major mineral needed in the daily diet

15 mg

amount of trace elements needed in the daily diet


a pure substance formed by chemically combining two or more elements together.

Chemical Formula

consists of element symbols to show the identity of the elements forming a compound and subscripts to show the ratio of atoms (the building blocks of matter) contained in the compound.


is a subatomic particle that holds a positive charge in an atom and is symbolized by p and has a charge that is = +1


is a subatomic particle that holds a negative charge in an atom and is symbolized by e-and has a charge that is = -1


is a subatomic particle that holds no charge in an atom and therefore has a charge that is = 0


a dense core that contains the protons and neutrons. Most of the mass of the atom resides here.

Electron Cloud

is composed of electrons that move rapidly in the almost empty space surrounding the nucleus. This comprises most of the volume of an atom.

Opposite Charges


Like Charges

These charges repel.

Atomic Number (Z)

tells us both the number of protons in the nucleus and the number of electrons in the electron cloud of a neutral atom.

Mass Number (A)

= the number of protons (Z) + the number of neutrons.


are atoms of the same element having a different number of neutrons

Atomic Weight

is the weighted average of the mass of the naturally occurring isotopes of particular element reported in atomic mass units.

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