Why is the size of noble gases greater than others of same period?

Answer 1

If by size you mean "mass", then Noble Gases have greater mass because they have more protons and neutrons in the nucleus. This follows the Periodic Trend across periods that mass increases from left to right. There are a few exceptions that can be found, which is why elements are ranked according to # protons and not mass.

If by physical size, then the answer gets more complicated. An atom's size is often measured using its atomic radius, which is the physical distance from the center of the nucleus to the outermost shell (aka "orbital" or "energy level"). By referencing the atomic radius, Noble Gases are actually SMALLER even though the nucleus is more massive. This is due to the electrostatic attraction between protons and electrons. As # protons increases the # electrons also increases. This increases the "tug of war" between the particles and causes the electrons to be held closer to the nucleus. This decreases the overall size, or radius, of the atom.

Answer 2

Even though atomic size decreases across a period due to increasing effective nuclear charge, the noble gases have the highest atomic size in their respective periods due to fact that they have achieved octet or duplet configuration and are extremely stable. They face electron-electron repulsion between their shells and they have van der waals radii rather than covalent or ionic radii.

Answer 3

Since Noble gases do not react,there is no OVERLAP of their atomic orbitals.Consequently,they will have a larger radius.

Answer 4

The noble gases are the largest of their period because they are the most stable and have the most electrons in that period.