How do we know the ionic charge of iron or elements such as iron on the periodic table?

How do we find iron's ionic charge? I was taught that we use roman numerals but I don't see any on the basic periodic table of elements (I'm using this one). So how do we find iron's charge of Fe 2+ or 3+? Again I thought it was the column that told us this but that doesn't seem like the case because iron's column numeral is VIII.

• Elements don't have "ionic charge". They can exhibit oxidation states and coordination numbers. While inorganic compounds are often treated like they were made of ions, that's hardly true. It's at best a lame approximation that easily outlives its usefulness. Sep 26, 2022 at 14:47

Epediaa states, "valence refers to the ability of an atom to be combined with another atom [which may vary, ed.] whereas valency refers to the maximum number of electrons that an atom can lose or gain in order to stabilize itself [a single value, ed.]." So an element has a specific valence, depending on its group (e.g., C, 4 or Xe, 0), but may have multiple values for valency, such as in $$\ce{FeCl2}$$ and $$\ce{FeCl3}$$, as you state
There are charts showing the most common valences, but take them with a grain of salt. For example, xenon, Xe, has a filled outer shell, ostensibly a valence of zero, yet over the last 50-or-so years, a number of Xe compounds have been discovered, such as $$\ce{XeF2}$$, $$\ce{XeF4}$$, and $$\ce{XeF6}$$.