Noble gases are elements in the last group of the periodic table.
Why are they the least reactive elements?
Noble gases have an octet configuration, which means they have maximum number of electrons in their outermost energy levels.
This makes them stable, which means they are inert.
Examples of noble gases include neon, argon, krypton, etc.
What is the Trend in reactivity in the periodic table?
Down the group from top to bottom
The reactivity of metals in the periodic table increases down the group due the increase in the number of energy levels which makes it easier for them to lose electron(s).
Non-metals react by gaining electron(s), therefore, their reactivity decreases down the group because as the energy level increases the nuclear charge decreases.
Across the period from left to right.
Reactivity of metals decreases across the period because of an increase in nuclear charge which makes it more difficult for them to lose electron(s).
On the other hand, reactivity of non-metals increases across the period due to increased nuclear charge that makes it easier for them to gain electron(s).
