The document discusses the organization of the periodic table. It explains that elements are organized into periods based on the number of electron shells and into groups based on the number of electrons in the outer shell. Transition metals follow slightly different rules regarding shells and valence electrons. Helium, though in group 18, only has two electrons due to its single electron shell.

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2. •Each row is called a “period”
•The elements in each period have
the same number of shells
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3. •Each column is
called a “group”
•Each element in a
group has the same
number of electrons
in their outer orbital,
also known as
“shells”.
Except for He, it
has 2 electrons
•The electrons in the
outer shell are called
“valence electrons”
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4. •Transition Metals
have slightly
different rules for
shells and
valence electrons.
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18. • Helium is the exception in Group 8.
• Since it has just one shell, that shell
can only fit 2 electrons instead of 8.
• It is in this group because all the
elements have a full outer shell.