GROUP 8A ELEMENTS - Noble Gases

By: Sam Haber, Ashley Kavanagh, and Theresa Jurewicz

The Group 8A Elements are more commonly known as the Noble gases, which include Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn). Noble gases are monatomic elements and are very nonreactive due to their complete valence electron shells, ns^2np^6 (1s^2 for Helium). The complete s and p orbitals form what is called a "stable octet". Ions which become isoelectronic to the any of the noble gases also share that same electron stability. (As shown in the diagram below, these colorless, odorless gases, also called the Inert Gases, have an oxidation number is 0 and do not readily form compounds.)
The only intermolecular forces present in the vacinity of Noble Gases are London Dispersion Forces, the strength of which is determined by the size of the atom itself. As the size of the atom increases, the more electrons there are, and, therefore the more powerful the attractive force that the atom exerts when it is polarized.

external image Noblefe.gif
Below is a table of all of the essential statistics of each of the Noble Gases, as well as Lithium and Fluorine for comparison. Some noticeable trends include that the Noble Gases all have small atomic radii, high ionization energies, no electron affinities, and very low melting and boiling points. In an atom, the attraction force of a proton is more than that of repulsion forces between each electrons or the centripical force keeping the electrons in orbit around the nucleus. This is the reason for the small atomic radii, and, therefore the high ionization energies (being closer to the nucleus, electrons would thus require more energy to be drawn away). The electron affinity for the Noble Gases is zero because of their complete s and p orbitals and the low temperature phase changing points for Noble Gases is due to weak intermolecular forces between them.


Helium
Neon
Argon
Krypton
Xenon
Radon
Lithium
Fluorine
Symbol
He
Ne
Ar
Kr
Xe
Rn
Li
F
Atomic Number
2
10
18
36
54
86
3
9
Atomic Weight (amu)
4.00
20.18
39.95
83.80
131.29
[222]
6.94
19.00
Atomic Radius (pm)
31
38
71
88
108
120
167
42
Density (g/L)
0.18
0.90
1.78
3.75
5.9
9.73
0.54 (g/ml)
1.70
Melting Point (degrees C)
none at STP
-248.59
-189.30
-157.36
-111.80
-71.00
180.54
-219.60
Boiling Point
-268.93
-246.08
-185.80
-153.22
-108.00
-61.70
1342
-188.12
Electronegativity
Unknown
Unknown
Unknown
3.0
2.6
Unknown
0.98
3.98
First Ionization Energy (eV)
24.59
21.57
15.76
14.00
12.13
10.75
5.391
17.422
Electron Affinity (eV)
0
0
0
0
0
0
0.618
3.4
Half-Life (days)
n/a
n/a
n/a
n/a
n/a
3.82
n/a
n/a
Abundance in Atmosphere
(% volume)
5 x 10^-4
1 x 10^-3
9 x 10^-1
1 x 10^-4
9 x 10^-6
1 x 10^-19


Examples of Compounds
none
none
HArF
KrF2
XeF6, XeF4,
XeO4, XeO3
RnF



external image 153px-Electron_shell_002_Helium_-_no_label.svg.png
external image 153px-Electron_shell_010_Neon_-_no_label.svg.png
external image 153px-Electron_shell_018_Argon_-_no_label.svg.png
external image 600px-Electron_shell_036_Krypton_-_no_label.svg.pngexternal image 153px-Electron_shell_054_Xenon_-_no_label.svg.pngexternal image 153px-Electron_shell_086_Radon_-_no_label.svg.png

Helium

Helium is not just used for hot air balloons or neon signs. It is a rather strategic element in that it is used as a cryogen for superconducting magnets, such as the ones use in the Large Hadron Collider, and in HeNe lasers. It can only obtained by separating it from natural gas in the ground and once it is released into the atmosphere it may as well be gone forever, since it rises and leaves the atmosphere. With increasing demand for the element as well as initial production costs makes Helium relatively expensive. Helium, named after the Greek sun god and rightly so, is also the second most abundant element in our sun, being that it is the product of the hydrogen nuclear fusion reaction. It is also the second most abundant element in the universe, after Hydrogen.

Helium Superfluid Video



Neon, Argon, Krypton

Neon, Argon, Krypton, and Xenon are obtained through fractional distillation of the air.
external image helium-neon-gas-laser.jpg
Neon is used, like Helium, as a cryogenic refrigerant, and has 40x the refrigerant capacity as Helium though not as cold. It is also used in HeNe lasers (seen to the right) and television tubes.

Argon, by far the most abundant Noble Gas, has a wide variety of uses. It is used whenever an inert gaseous environment is needed, like for the growing of Silicon and Germanium crystals. It is also used in industrial arc welding and as laboratory shielding between two panels of glass. Argon is used in industrial strength lasers.

Krypton, (no we're not talking about Superman) due to its brillance when an electric current is induced, is used in high-intensity lasers, airport runway lights, and in high efficiency lighting.

Xenon and Radon

external image 300px-Xenon_tetrafluoride.gif
Xenon is used in electron tubes, bactericidal lamps, Imax cinema projectors,
and it is used to excite ruby-lasers. Xenon is one of the more interesting Noble Gases because of its ability to form a variety of covalent bonds with Oxygen and Fluorine. In 1962, Neil Bartlett, sythesized the first compound of Xenon purely by chance. He was looking for another agent in a reaction with PtF6 and found that Xenon could replace the Oxygen in the original reaction due to its similar first ionization energy. The reaction did not go as he had expected it to, but the first compound, a solid containing Xenon, was formed. Perxenate ions (XeO6-), are used today as an oxidizing agent in analytical chemistry. Most of Xenon's compounds, as well as other Nobel Gas compounds, are only used for scientific research. (Xenon Tetrafluoride crystals seen to the right.)

Radon is the only radioactive gas, let alone Nobel Gas, discovered. It has a half-life of about 3.2 days and is produced from the decay of Uranium and Thorium. Radon seeps up from the ground, most notably from granite rock and hot springs. Radon was commonly used in cancer radiotherapy treatment, until safer methods were developed.

Noble Gas Video


Questions

1.What do all Noble Gases have?
a) Low ionization energies.
b) The same electronegativity.
c) High radioactivity.
d) Small atomic radii.

2. Which element is used in airport runway lights?
a) Xenon.
b) Krypton.
c) Neon.
d) Radon.

3. Which Noble Gas has the highest boiling point?
a) Radon.
b) Helium.
c) Lithium.
d) Argon

4.What is the electron configuration for Helium?
a)1s^2, 2s^2
b) 1s^2, 2s^2, 2p^6
c) 1s^2
d) 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^1

5. The complete orbitals of noble gases are called:
a) full owlet
b) full octet
c) full ocelot
d) full oncet


Works Cited

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"Experimental Feature: (Helium, Neon, Argon, Krypton, Xenon, Radon, Lithium, Fluorine)."
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<http://www.wolframalpha.com/>.

Gerkin, Dr. M. Chemistry 3830 Lecture Notes. N.p.: n.p., n.d. PDF.

"Krypton." - Uses, Pictures, Characteristics, Properties, Periodic Table. N.p., n.d. Web. 27 Nov. 2012.
<http://www.lookchem.com/Periodic-Table/Krypton/>.

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<http://chemistry.about.com/od/elementfacts/a/neon.htm>.

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<http://www.iun.edu/~cpanhd/C101webnotes/chemical-bond/noble-gas-rule.html>.

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<http://www.chemicalelements.com/groups/noblegases.html>.

"Noble Gases." About.com Chemistry. N.p., n.d. Web. 27 Nov. 2012.
<http://chemistry.about.com/od/elementgroups/a/noblegases.htm>.

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<http://chemistry.about.com/od/elementfacts/a/xenon.htm>.

Zumdahl, Steven S., and Susan A. Zumdahl. "Chapter 20: The Representative Elements." AP* Edition
Chemistry. 8th ed. Belmont, CA: Brooks Cole, 2012. 940-43. Print.