Different Forms of the Same Element •  In any element, the # of protons is always constant. •  Unlike the number of protons, the number of electrons and neutrons can vary within an element without changing the idenAty of the element. –  Ex. Carbon (C) ALWAYS has 6 protons, but it can have anywhere from 6-­‐8 neutrons and 2-­‐10 electrons Isotopes •  An ISOTOPE is a form of an element that has a different number of neutrons than “normal” •  Carbon has three isotopes Notice how the # of
protons does NOT
change!
Nuclear Symbols Isotopes are atoms with the same number of protons but
different number of neutrons
A X Z A = mass number
(the total number of protons + neutrons)
Z = atomic number
(the total number of protons)
X = element symbol
Hyphen NotaAon Another way to represent an isotope
is using hyphen notation. This
involves: Element-Mass #
Example
• Nuclear Symbol
• Hyphen Notation Chlorine-35
Another example of a nuclear symbol and
hyphen notation for same isotope.
Beryllium-9
Determine the number of neutrons in
Argon-40.
The atomic number for argon is 18.
40 - 18 = 22.