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.
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1$\begingroup$ 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. $\endgroup$– MithoronSep 26, 2022 at 14:47
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It's not simply the column that determines the ionic charge of an element, but also other factors, such as row and with what other elements it's combined.
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 $\ce{XeF6}$.
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So there's no simple rule for learning the number of electrons an atom may gain or lose in a compound (and using electricity, for example, it's possible to remove electrons well below the valence shell), though the number of electrons in the valence shell is unique.
answered Sep 25, 2022 at 2:28
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$\begingroup$ So if it were FeCl3, that would mean that it's Fe3+ because Cl3 is -3, so Fe has to cancel with positive three, thus Fe3+. Am I Correct? and wasn't the simple rule that if it is the first three columns excluding transition and the elements with carbon-silicon etc., then it (+) and otherwise it's (-) because they gain one more due to them having an imbalance. $\endgroup$– AbdullahSep 25, 2022 at 15:20
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$\begingroup$ Yes, Fe+3 in FeCl3, and Fe+2 in FeCl2. The first few rows tend to follow general rules, but consider carbon monoxide, or all the different oxides of nitrogen. en.wikipedia.org/wiki/Nitrogen_oxide $\endgroup$ Sep 25, 2022 at 16:24