A substance that cannot be broken down into simpler substances by chemical means. An element is composed of atoms that have the same atomic number, that is, each atom has the same number of protons in its nucleus as all other atoms of that element. Today 115 elements are known, of which 92 are known to occur in nature, while the remainder have only been made with particle accelerators. Eighty-one of the elements have isotopes that are stable. The others, including technetium, promethium, and those with atomic numbers higher than 83, are radioactive. See Periodic Table .
• Request a white board if you plan to jot down notes during the examination. Please note}
that you must complete the tutorial and accept the Non-Disclosure Agreement (NDA)
prior to writing any notes. Once the 15 minute tutorial is complete there is a five minute
window to accept the NDA. If the NDA is not signed within the appropriate window of
time your examination ends and you will be escorted out of the testing room, forfeit
your fees and eligibility. Test centers are using white boards (rather than paper) in an
effort to "go green."