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Now that you have explored the pattern of electron arrangements across the periodic table, you can use those patterns to understand the properties of different groups. Begin with the least reactive elements found in group 18 to the far right of the periodic table.
Now that you have explored the pattern of electron arrangements across the periodic table, you can use those patterns to understand the properties of different groups. Begin with the least reactive elements found in group 18 to the far right of the periodic table.
Figure 25 The noble gases are the elements in group 18 of the periodic table.
The elements in group 18 are known as the noble gases. In nature, these elements are found as single atoms. Argon, krypton, xenon, and radon can, under certain conditions, link to other elements to form very unstable substances. Helium and neon have been made to bond to other atoms to form unusual substances under extreme conditions. These elements are, by far, the most unreactive group.
You can understand why these elements are unreactive when you examine their electron arrangements. Helium is the only noble gas with two valence electrons, which, in this case, constitutes a full outer shell. The remaining noble gases also have full sets of valence electrons. In other words, the outermost shell of every noble gas is completely filled with electrons. This causes these elements to be inert: they do not gain, lose, or share electrons.
Table 4: Physical properties of the noble gas elements
Table 4 summarizes some physical properties of some noble gases. You can see from the melting and boiling points that the noble gases must be cooled to extremely low temperatures before they condense from a gas to a liquid. At that point, it only takes a further decrease of a few degrees to freeze these elements into solids. Thus, these elements exist as gases under normal conditions.
Trends in the melting and boiling points of the elements can be seen as you move down within the group. The trends show that the larger the atomic radius of the noble gas is, the higher its melting point and boiling point are.
As explained earlier, the exact size of an atom cannot be determined because of the atom’s lack of defined boundaries. Instead, scientists make their best judgment of the atomic radius of an element from data gathered about the element. The table above shows atomic radii determined for the noble gases. From these data, you can see that atomic radius increases with increasing atomic number. This trend can be explained by the increasing number of electrons filling more energy levels as you move down within the group. Each energy level that must be added to accommodate more electrons tends to increase the volume of space the atom takes up, thus increasing its radius.
Because of their lack of reactivity, noble gases are used whenever an inert atmosphere is needed. For example, argon is pumped into light bulbs before they are sealed and helium is used to fill large weather balloons and airships known as dirigibles or blimps. A 1937 disaster in which a hydrogen-filled dirigible caught fire and exploded made it clear that hydrogen was not a suitable gas for airships. Dirigibles are now filled with helium, a gas that is much safer due to its inert property.
Which element needs colder conditions to solidify, helium or krypton?
The element that needs colder conditions to solidify is
.
answer :
helium
Which of the following statements is/are true about elements of group 18 of the periodic table?
When you move down the group, the atomic radius increases.
They share electrons with one another.
When you move down the group, the atomic radius stays constant.
They are the most unreactive elements.
answer :
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