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Atoms of the same element.
• Same number of protons (same atomic #)

• Different numbers of neutrons (different mass #’s)

Nuclide names

Nuclide symbols

Mass Numbers (different)

Isotope notations Atomic Number (same).
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Number of Protons.

# of Neutrons (different)
(Mass# - Atomic #)

11 p 11 p
Nuclear diagrams
12 n 13 n

The average mass of an element’s naturally occurring
isotopes.

22.898 Can be found on the Periodic Table
or
Na Can be calculated from mass numbers and percent
23 abundances of an element’s natural isotopes.

th
1
1 amu = /12 the mass of Carbon–12

3 shell
rd

Energy levels of an atom. 2 shell
nd

st
1 shell

Atomic model of an element
that shows all the electron shells.
2 e-
Bohr’s diagram for Sodium (Na)

8 e-
is shown on the right.
1 e-

The arrangement of electrons 2 – 8 – 1 # of e-
in the electron shells of an atom.
1 2 3 shell
rd
st
nd

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