Multiple Choice
What is the purpose of the Roman numeral within the name of an ionic compound?
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3. Chemical Reactions
Naming Ionic Compounds
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Which of the following is the correct chemical formula for the ionic compound formed between sodium (Na) and sulfur (S)?
A
Na2S
B
Na2S2
C
NaS2
D
NaS
Verified step by step guidance1
Identify the charges of the ions formed by sodium and sulfur. Sodium (Na) is an alkali metal that typically forms a +1 cation, written as Na\^{+}. Sulfur (S) is a nonmetal that typically forms a -2 anion, written as S\^{2-}.
Determine the ratio of sodium ions to sulfur ions needed to balance the overall charge of the compound. Since sodium has a +1 charge and sulfur has a -2 charge, you need enough sodium ions to balance the -2 charge from one sulfur ion.
Set up the charge balance equation: Let the number of sodium ions be x and the number of sulfur ions be y. The total positive charge is +1 \times x and the total negative charge is -2 \times y. For the compound to be neutral, these must sum to zero: 1 \times x + (-2) \times y = 0.
Solve the charge balance equation for the smallest whole number ratio. If y = 1 (one sulfur ion), then x must be 2 (two sodium ions) to balance the charge: 2 \times (+1) + 1 \times (-2) = 0.
Write the chemical formula using the ratio found. Since there are 2 sodium ions for every 1 sulfur ion, the formula is Na\_2S.
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