How do you determine the charges of an element without looking at the periodic table?

Like for example, I have Cr. Without looking at the table, how can I know what the charge is on it?



DON'T JUST TELL ME THE NUMBER, TELL ME HOW TO FIND IT WITHOUT USING THE TABLE.How do you determine the charges of an element without looking at the periodic table?
Group 1 all have +1

Group 2 all have +2

Oxygen's group has -2

Florine's group has -1

Aluminum has +3How do you determine the charges of an element without looking at the periodic table?
Know the charge of the molecule it is bonded to, and subtract that from 8.
Other than memorizing the properties, there is no way. That is why the periodic table is so valuable.
It's just something you have to learn by heart, unfortunately. Once you become more familiar with the elements, you'll be able to remember the charges of the ones that come up most often in your field.



You can however deduce the charge of an atom if you know the charges of other atoms in a molecule, and if you know the charge of the molecule itself. For example, if you have H2O, and you know Oxygen ion has two unpaired electrons giving it a charge of -2, in order for water to have no charge each Hydrogen must have a charge of +1 to balance the molecule. Make sense?



Here's another example, suppose you need to know the charge of sodium ion, but can never remember it. You know that salt, NaCl, has no net ionic charge, and you know that all of the halogens have a charge of -1. Chlorine is a halogen (along with flourine, bromine, iodine, etc), so for NaCl to have no net charge, Sodium ion must have a charge of +1.



In regards to Chromium, and all of the other metals, there is no way to know without memorizing them. Metals are troublesome that way.
If you have the number of protons (+) and the number of electrons (-), then you just find the difference. If there are more electrons, the element is negative. If there are more protons, the element is positive.
Other than memorizing it there is not really a way. If you know its position on the table, how many valance electrons it has then that can be helpful. Cr has two oxidation states 2+ and 3+ this is because it can lose its s electrons 1st that is 2+ then it will lose one d electron. As you begin to become more familiar with ways in which d block elements gain stability there are definite patterns.