The Atom, the Nucleus and Radioactivity Flashcards
Emission Spectrum
When light from a luminous source undergoes dispersion the resulting pattern is called an emission spectrum
Energy Level
An energy level is a fixed energy value that an electron can have in an atom
Atomic Number
The atomic number (Z) of an element is the number of protons in the nucleus of an atom of that element
Mass Number
The total number of protons and neutrons in the nucleus of an atom is called the mass number (A) of that atom
Isotopes
Atoms of an element that have the same number of protons but different numbers of neutrons are called isotopes of that element
Radioactivity
Radioactivity is the disintegration or decay of the nuclei of certain atoms with the emission of one or more types of radiation
Alpha Radiation
Alpha radiation is fast moving helium nuclei ejected from the nuclei of radioactive atoms
Beta Radiation
Beta radiation is high-speed electrons ejected from the nuclei of radioactive atoms
Gamma Radiation
Gamma radiation is high-frequency electromagnetic radiation (with frequencies above those of normal x-rays) emitted from the nucleus of a radioactive atom
Activity
The activity (A) of a radioactive substance is the number of nuclei of that substance decaying per second
Unit of Activity
The unit of activity is the becquerel (Bq)
1 becquerel is equal to 1 radioactive disintegration per second
Half-Life
The half-life of a radioactive isotope is the time taken for half of the undecayed atoms to undergo decay
The half-life of a radiactive element is also the time taken for its activity to decrease by half
The Mole
A mole of any substance is the amount of that substance that contains as many particles as there are atoms in exactly 12 grams of Carbon 12. The number is
6.02 x 10*23, and is called Avogadro’s number
