Periods are the horizontal rows on the periodic table of elements.  Elements in the same period have the same number of electron shells/orbitals.

The group/family number is the number assigned to the vertical columns of the periodic table.  Elements within the same group have the same number of valence electrons.  This similar electron configuration leads to the elements in the same group having similar chemical properties. 

Look through your notes at the observations that you made in Activity 1.  Did elements in the same group have similar properties?  If so, which properties where similar?

Notice the similar electron configurations in the image of the noble gases below.  The fact that all the noble gases have complete outer energy shells leads to similar properties: one of which is that the noble gases are considered to be extremely stable elements.

Chemical Elements of the Six Noble Gases
(Group 18 of the Periodic Table)

Helium - He An atom with two protons in the nucleus, and two electrons in the first energy level.	Neon - Ne An atom with ten protons in the nucleus, two electron in the first energy level, and eight electrons in the second energy level.
Argon - Ar An atom with ten protons in the nucleus, two electrons in the first energy level, eight electrons in the second energy level and eight electrons in the third energy level.	Krypton - Kr An atom with 36 protons in the nucleus, two electrons in the first energy level, eight electrons in the second energy level, eight electrons in the third energy level and eight electrons in the fourth energy level.
Xenon – Xe An atom with 54 protons in the nucleus, two electrons in the first energy level, eight electrons in the second energy level, eight electrons in the third energy level, eight electrons in the fourth energy level and eight electrons in the fifth energy level.	Radon – Rn An atom with 86 protons in the nucleus, two electrons in the first energy level, eight electrons in the second energy level, eight electrons in the third energy level, eight electrons in the fourth energy level, eight electrons in the fifth energy level and eight electrons in the sixth energy level.

Location of the Noble Gases on the Periodic Table: