READ: Noble Gases
READ: Noble Gases
What Are Noble Gases?
Noble gases are nonreactive, nonmetallic elements in group 18 of the periodic table. As you can see in the periodic table below, noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All noble gases are colorless and odorless. They also have low boiling points, explaining why they are gases at room temperature. Radon, at the bottom of the group, is radioactive, so it constantly decays to other elements. For an excellent overview of the noble gases, watch this video:
Q: Based on their position in the periodic table, how many valence electrons do you think noble gases have?
A: The number of valence electrons starts at one for elements in group 1. It then increases by one from left to right across each period (row) of the periodic table for groups 1–2 and 13–18. Therefore, noble gases have eight valence electrons.
Chemical Properties of Noble Gases
Noble gases are the least reactive of all known elements. That’s because with eight valence electrons, their outer energy levels are full. The only exception is helium, which has just two electrons. But helium also has a full outer energy level, because its only energy level (energy level 1) can hold a maximum of two electrons. A full outer energy level is the most stable arrangement of electrons. As a result, noble gases cannot become more stable by reacting with other elements and gaining or losing valence electrons. Therefore, noble gases are rarely involved in chemical reactions and almost never form compounds with other elements.
Some Uses of Noble Gases
Did you ever get helium balloons? Unlike a balloon filled with air, a balloon filled with helium needs to be weighted down so it won’t float away.
Q: Why does a helium balloon float away if it’s not weighted down?
A: Helium atoms have just two protons, two neutrons, and two electrons, so they have less mass than any other atoms except hydrogen. As a result, helium is lighter than air, explaining why a helium balloon floats up into the air unless weighted down.
Noble gases are also used to fill the glass tubes of lighted signs like the one in the below. Although noble gases are chemically nonreactive, their electrons can be energized by sending an electric current through them. When this happens, the electrons jump to a higher energy level. When the electrons return to their original energy level, they give off energy as light. Different noble gases give off light of different colors. Neon gives off reddish-orange light, like the word “Open” in the sign below. Krypton gives off violet light and xenon gives off blue light.
Summary
- Noble gases are nonreactive, nonmetallic elements in group 18 of the periodic table.
- Noble gases are the least reactive of all elements. That’s because they have eight valence electrons, which fill their outer energy level. This is the most stable arrangement of electrons, so noble gases rarely react with other elements and form compounds.
- The octet rule states that atoms react to form compounds that allow them to have eight valence electrons like the noble gases, which are the least reactive elements.
- Noble gases are used for balloons, light bulbs, and lighted signs.
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