Periodic Trends: Atomic Size & Ionic Charge
Periodic trends are specific patterns that are present in the periodic table, which illustrate different aspects of a certain element, including its size and its properties with electrons. The main periodic trends include: electronegativity, ionization energy, electron affinity, atomic radius,melting point, and metallic character. The periodic trends that arise from the arrangement of the periodic table provide chemists with an invaluable tool to quickly predict an element's properties. These trends exist because of the similar atomic structure of the elements within their respective group families or period and the periodic nature of the elements.
Atomic size
The atomic radius is the distance from the atomic nucleus to the outermost stable electron orbital in an atom that is at equilibrium. The atomic radii tends to decrease across a period from left to right. The atomic radius usually increases while going down a group due to the addition of a new energy level (shell). However, diagonally, the number of electrons has a larger effect than the sizeable radius. For example, lithium has a smaller atomic radius than magnesium.
Radius decreases across a period.
Increase effective nuclear charge due to decreased shielding.
Radius increases down a group.
Each row in periodic table adds a shell or energy level to the atom.
As you can see in this picture the atomic radius/atomic size increases from top to bottom and decreases from left to right across the periodic table. This is caused by electron shielding.
Ionic charge/Ionic radius
Ionic charge—the number of electrons an element tends to gain or lose is a periodic property. The ionic radius is the measure of an atom's ion in a crystal lattice. Values for ionic radius are difficult to obtain and tend to depend on the method used to measure the size of the ion.
As you move down a group in the periodic table, additional layers of electrons are being added, which naturally causes the ionic radius to increase as you move down the periodic table.
As you move across a row of period of the periodic table, the ionic radius decreases for metals forming cations, as the metals lose their outer electron orbitals. The ionic radius increases for nonmetals as the effective nuclear charge decreases due to the number of electrons exceeding the number of protons.
