THE NOBLE GASES – GROUP 0
In this group, we have Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn). The electronic configuration will show that these atoms all have a complete outer shell of electrons and are not interested in reacting with other elements.
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These elements are therefore chemically non-interacting and inert. They are therefore gaseous in nature. They are Noble gases or inert gases They are all colourless monatomic gases. Monatomic means that they exist as single atoms. The forces between the atoms are very weak (and so they are gases).
Going down the group from helium to radon, the density increases. The melting and boiling point increases because the atoms become heavier (bigger) and require more energy to melt or boil.
Summary of Noble Gases
- The “Noble Gases” are the last group in the Periodic Table i.e. they form the last elements at the end of a period.
- They are all non-metallic elements and all are colourless gases at room temperature and pressure with very low melting points and boiling points.
- They form 1% of air, and most of this is argon. All the noble gases, except radon, are separated by the fractional distillation of liquefied air.
Helium can also be obtained from natural gas wells where it has accumulated from radioactive decay (alpha particles become atoms of helium gas when they gain two electrons).
- They are very unreactive elements because the highest occupied electron level is complete, meaning they have a full shell of outer electrons!
They have no ‘wish’ electronically to share electrons to form a covalent bond or to lose or gain electrons to form an ionic bond. In other words, they are electronically very stable.
- They exist as single atoms, i.e. they are monatomic He Ne Ar etc.
(NOT diatomic molecules as with many other gases).
- Their very inertness is an important feature of their practical uses.
- Down the Group with increasing atomic number:
- the melting point and boiling point steadily increase (see data)
- the density steadily increases
- more likely to react and form a compound with very reactive elements like fluorine
Variation of Atomic Radius down the Group
As we move down the group, the atoms get bigger as more electron shells are added. One full shell i.e. a set of 8 electrons is added from one element to the next. This means that the atomic number and mass number both increase as we move down the group. We can observe here that all the group member elements have the same valence electrons and display same valencies.
Metallic Character and Electronegativity
Ongoing down a particular group, the properties of elements get enhanced. For example, the figure below shows group I A, the alkali metal elements. As the atomic radii increases in the alkali metal elements, the last electron is farther away from the attractive forces of the nuclear charge. So it is relatively easy for the element to give up its last electron. And hence show more metallicity.
To say it in terms of electro positive character of elements, we can say that the electro positive character increases as we go down the group I. Now if we see the behaviour of elements in the group VII or the halogen elements, we see that the electro negative character reduces as we go down the group. This means that fluorine (F) is more reactive than chlorine (Cl). The reason for this is that the orbit where the extra electron is captured is closer to the nucleus in F than in Cl. Thus the extra electrons get attracted into the F-atom in a stronger manner than that in Cl.
Reactivity down the Group
As far as chemical reactivity is concerned, we can see that in group I, the reactivity increases as we go down the group. On the other hand, in the other extreme, in group VII A, the reactivity decreases as we go down the group. Also group VIII A consisting of noble gases is completely unreactive.
Summary of the characteristics of elements in a group
- The atomic numbers are not consecutive.
- The number of valence electrons in the elements is same in a group.
- The elements of the same group have the same valencies. The atomic radii increase while going from top to bottom in a group.
- Metallic character increases while going from top to bottom in a group for metallic groups.
For non-metallic groups, the non-metallic nature decreases while going from top to bottom
- Chemical reactivity increases while going from top to bottom in a group for metallic groups.
For non-metallic groups, the chemical reactivity decreases while going from top to bottom.