CHEMISTRY -PERIODIC TABLE - NOBLE GASES #4

The Noble Gases

We love the noble gases. Some scientists used to call them the inert gases. It didn't really work because there are a few other gases that are basically inert but not noble gases.
Nitrogen (N₂) might be considered an inert gas, but it is not a noble gas. 

The noble gases are another family of elements, and all of them are located in the far right column of the periodic table. For all of you budding chemists, the far right is also known as Group Zero (Group 0) or Group Eighteen (Group XVIII). This family has the happiest elements of all. 

Why Are They Happy?

Using the Bohr description of electron shells, happy atoms have full shells. All of the noble gases have full outer shells with eight electrons. 
Oh, wait! That's not totally correct. At the top of the noble gases is little helium (He), with a shell that is full with only two electrons. The fact that their outer shells are full means they are quite happy and don't need to react with other elements. In fact, they rarely combine with other elements. That non-reactivity is why they are called inert. 

Who's in the Family?

All of the elements in Group Zero are noble gases. The list includes helium, neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Don't think that, because these elements don't like to react, we don't use them. You will find noble gases all over our world. Neon is used in advertising signs. Argon is used in light bulbs. Helium is used in balloons and to cool things. Xenon is used in headlights for new cars. Because of their chemical properties, these gases are also used in the laboratory to help stabilize reactions that would usually proceed too quickly. When you move down the periodic table, as the atomic numbers increase, the elements become rarer. They are not just rare in nature, but rare as useful elements, too. 

But Wait, They Do Bond!

Some do. As of about 40 years ago, scientists have been able to make some compounds with noble gases. Some have been used in compounds to make explosives, and others just form compounds in a lab. The thing to remember is that they were forced. When going about their natural lives, you will never (well, never say never, because there may be an exception) find the noble gases bonded to other elements. 

PUZZLE PRACTICE

CHEMISTRY - ELEMENT OF THE DAY - ARGON

18

Ar

Argon

39.948

Atomic Number: 18

Atomic Weight: 39.948

Phase at Room Temperature: Gas

Element Classification: Non-metal

Period Number: 3    Group Number: 18    

Group Name: Noble Gas

What's in a name? From the Greek word for inactive, argos.

Say what? Argon is pronounced as AR-gon.

History and Uses:

Argon was discovered by Sir William Ramsay, a Scottish chemist, and Lord Rayleigh, an English chemist, in 1894. Argon makes up 0.93% of the earth's atmosphere, making it the third most abundant gas. Argon is obtained from the air as a byproduct of the production of oxygen and nitrogen.

Argon is frequently used when an inert atmosphere is needed. It is used to fill incandescent and fluorescent light bulbs to prevent oxygen from corroding the hot filament. Argon is also used to form inert atmospheres for arc welding, growing semiconductor crystals and processes that require shielding from other atmospheric gases.

Once thought to be completely inert, argon is known to form at least one compound. The synthesis of argon fluorohydride (HArF) was reported by Leonid Khriachtchev, Mika Pettersson, Nino Runeberg, Jan Lundell and Markku Räsänen in August of 2000. Stable only at very low temperatures, argon fluorohydride begins to decompose once it warms above -246°C (-411°F). Because of this limitation, argon fluorohydride has no uses outside of basic scientific research.

CHEMISTRY - PERIODIC TABLE - HALOGENS #3

Halogens on the Right

In the second column from the right side of the periodic table, you will find Group Seventeen (Group XVII). 

This column is the home of theHalogen family of elements. 

Who is in this family? The elements included are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). 

What Makes Them Similar?

When you look at our descriptions of the elements fluorine and chlorine, you will see that they both have seven electrons in their outer shell. That seven-electron trait applies to all of the halogens. They are all just one electron shy of having full shells. Because they are so close to being happy, they have the trait of combining with many different elements. They are very reactive. You will often find them bonding with metals and elements from Group One of the periodic table. The elements in the column on the left each have one electron that they like to donate. 

We've just told you how reactive the halogens are. Not all halogens react with the same intensity or enthusiasm. Fluorine is the most reactive and combines with most elements from around the periodic table. Reactivity decreases as you move down the column. As you learn more about the table, you will find this pattern true for other families. As the atomic number increases, the atoms get bigger. Their chemical properties change just a little bit when compared to the element right above them on the table. 

What is a Halide?

The elements we are talking about in this section are called halogens. When a halogen combines with another element, the resulting compound is called a halide. One of the best examples of a halide is sodium chloride (NaCl). Don't think that the halogens always make ionic compounds and salts. Some halides of the world are a part of molecules with covalent bonds. 

PUZZLE PRACTICE

QUIZ - HALOGENS