How does the atomic size of noble gases change across the group?

The atomic size of noble gases increases as you move down the group.

In the periodic table, noble gases are found in Group 18. These include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). As you move down this group from helium to radon, the atomic size or atomic radius of these elements increases. This is due to the addition of energy levels (shells) around the nucleus.

The atomic size is determined by the distance between the nucleus of an atom and its outermost shell where the valence electrons are located. In noble gases, each subsequent element down the group has an additional energy level compared to the one before it. For example, helium has one energy level, neon has two, argon has three, and so on. Each additional energy level is further away from the nucleus, which increases the atomic size.

Furthermore, the increase in atomic size is also due to the shielding effect. As more energy levels are added, the inner electrons 'shield' the outer electrons from the positive charge of the nucleus. This reduces the pull of the nucleus on the outer electrons, allowing them to drift slightly further away, which in turn increases the atomic radius.

However, it's important to note that the increase in atomic size does not affect the reactivity of noble gases. They are known for their low reactivity due to having a full outer shell of electrons, which makes them stable and unlikely to form bonds with other elements. This characteristic is consistent across the group, regardless of the atomic size.