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My teacher said that on the periodic table there is a "nose" formed by Al, Zn, Ag, and Cd. She said that they are all fixed charged (+3, +2, +1, and +2 respectively), and said that if I write them in ionic equations, I just say Silver Nitrate instead of Silver (I) Nitrate. She also said to put all Al as +3 charge in all cases, etc. But I did some research and found out that you do say Silver (I) Nitrate (actually both are fine, but my teacher specifically said never put the (I) in such cases). So is my teacher wrong? And are there cases where the charges of the elements are not what my teacher says?

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    $\begingroup$ Saying "silver (I) nitrate" is certainly not wrong, just redundant. Yes there are cases where Ag has charge other than +1, but you probably won't ever encounter them. $\endgroup$ – Ivan Neretin Nov 13 at 6:16
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    $\begingroup$ @BadAtChemistry "Silver(I) nitrate" is definitely not wrong and all of the elements have at least one more oxidation state, zero. As for the noses, tails and other mnemonics used to remember stuff I find them counterproductive and sometimes even harmful. $\endgroup$ – andselisk Nov 13 at 6:19
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    $\begingroup$ For regular chemistry, there are not such cases as simplification. For advanced chemistry, there are such cases, like silver (II) or silver(III). Search for advanced resources of element chemistry. $\endgroup$ – Poutnik Nov 13 at 6:20
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    $\begingroup$ See e.g Ag4O4,( Silver(I,III) oxide), AgF2 or KAgF4. $\endgroup$ – Poutnik Nov 13 at 6:29
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    $\begingroup$ In probably ten minutes of SciFindering, I could find an exception for each of those elements. But as you have a teacher you’re probably at school so two very old rules apply: 1) you are learning very simplified concepts; and 2) the teacher is always right. $\endgroup$ – Jan Nov 13 at 17:03
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All of these elements can form compounds in other oxidation states. Aluminium forms some compounds in the +1 state (e.g. see the section in https://en.wikipedia.org/wiki/Aluminium_iodide), as does Zinc (see the section in https://en.wikipedia.org/wiki/Compounds_of_zinc) and Cadmium (e.g. https://en.wikipedia.org/wiki/Cadmium(I)_tetrachloroaluminate). But Silver is the element that shows this most often in the list given - for instance it forms fluorides in the +1, +2 and +3 oxidation states (https://en.wikipedia.org/wiki/Silver_fluoride). As such I wouldn't say including the oxidation states in the formula is wrong, but on the other hand if you omit it everybody who knows there is an ambiguity will understand what is implied.

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