4 The Nucleus & The Periodic Table Atomic number and atomic mass describe the structure of the nucleus of each elementAtomic number tells the number of protons in the nucleus (always a whole number)Atomic mass tells the number of protons and neutrons in the nucleus (always a decimal number)To figure out the average number of neutrons in a particular element, subtract the atomic number from the atomic mass
6 Element, Isotope, IonAtoms with different numbers of protons are called “elements”Elements differ by the number of protons in the nucleusAtoms with different numbers of neutrons in the nucleus are called “isotopes”Atoms with different numbers of electrons are called “ions”
7 Elements, Isotopes, Ions NaISOTOPES of SODIUMNa+
8 Writing IsotopesThe number of neutrons and protons in a particular atom (in this case, uranium) is written concisely as follows:Number ofProtons + neutronsAtomic MassNumber of protonsAtomic Number
9 SummaryEach different element has a different number of protons in its nucleusA single element has the same number of protons in its nucleus, but can have different numbers of neutrons. Each atom with different numbers of neutrons is called an isotopeThe atomic number equals the number of protons in the nucleusThe atomic mass equals the number of protons + the number of neutrons in the nucleus
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