Strontium bromide contains only strontium and bromine. What is the formula for this compound?
Express your answer as a chemical formula.
Ionic compounds are always made up of a cation (positive ion) and an anion (negative ion). The cation is always listed first in the formula. The hard part about writing ionic formulas is determining how many of each ion is needed to make a neutral compound. In Na2S, the cation is Na + and the anion is S2−. Na forms a cation with a +1 charge because it must lose an electron to achieve 10 electrons like Ne, the nearest noble gas to Na in atomic number. S forms an anion with a −2 charge because it must gain two electrons to have 18 electrons like Ar, the nearest noble gas to S in atomic number.
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