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Matter, Elements, and Atoms:
Matter is anything that occupies space and has mass.Mass refers to the amount of matter in an object.Matter is composed of elements, basic substances that cannot be broken down into simpler substances by ordinary chemical means.An atom is a smallest unit of an element that retains the chemical characteristics of that element.
Some of elements critical to proper body function are oxygen, carbon,nitrogen,hydrogen,phosphorus.
The nucleus of an atom contains positively charged protons and uncharged neutrons.Orbiting the nucleus are negatively charged electrons.
An atom atomic number indicates the number of protons in its nucleus.Atomic weight is calculated by adding the number of protons and the number of neutrons in the nucleus.
Isotopes are atoms of an element that have the typical number of protons and electrons but different of neutrons.Radioactive isotopes have nuclei that are undergoing changes called "decay"
The electrons of atoms are distributed around the nucleus in layers called electron shells.
The number of electrons in the outermost shell determines how one atom will react with another atom.Atom that have a filled outer shell are stable.
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