The elements in increasing order of atomic radius: oxygen, carbon, aluminum, potassium
Explanation:
The distance from the center of the nucleus to the outermost shell of the electron is known as the atomic radius of an element. The atomic radius decreases rightward along each period (row) of the table due to the increase in effective nuclear charge (the charge of the nucleus equal to the number of protons). Across a period, electrons are added to the same energy level and the increasing number of protons causes the nucleus to exert more pull on these electrons, which makes the atomic radius smaller. Atomic radius increases down each group (column) of the periodic table because of the addition of electrons to higher energy levels, which are further away from the nucleus and the pull of nucleus weakens. Another reason for the increase in atomic radius is the electron shielding effect, which is the reduction of the attractive force between a nucleus and its outer electrons due to the blocking effect of inner electrons
While moving from left to right in the second period, c
arbon comes before oxygen and so oxygen will have a smaller atomic radius than carbon. While moving down the periodic table, al
uminum comes before potassium even if they are not in the same period. So aluminum
's atomic radius will be smaller than that of potassium but bigger than that of carbon and oxygen.
