Question

Identify each case in which the formula is incorrect. Give the correct formula for the indicated name. a. silver oxide, \(\mathrm{SiO}_{2}\) b. sodium sulfide, \(\mathrm{Na}_{2} \mathrm{S}\) c. barium oxide, \(\mathrm{B}_{2} \mathrm{O}_{3}\) d. calcium nitride, \(\mathrm{Ca}_{3} \mathrm{N}_{2}\) e. lithium bromide, \(\mathrm{Li}_{3} \mathrm{B}\)

Short answer

a. Incorrect: \(\mathrm{SiO}_{2}\). Correct: \(\mathrm{Ag}_{2}\mathrm{O}\) (silver oxide) b. Correct: \(\mathrm{Na}_{2}\mathrm{S}\) (sodium sulfide) c. Incorrect: \(\mathrm{B}_{2} \mathrm{O}_{3}\). Correct: \(\mathrm{BaO}\) (barium oxide) d. Correct: \(\mathrm{Ca}_{3} \mathrm{N}_{2}\) (calcium nitride) e. Incorrect: \(\mathrm{Li}_{3} \mathrm{B}\). Correct: \(\mathrm{LiBr}\) (lithium bromide)

Step-by-step solution

Identify the error

Deconstruct the formula to find its individual elements. The chemical symbols do not match the elements given in the name. We have silicon (Si) and oxygen (O) instead of silver (Ag) and oxygen (O).

Correct the formula

Rewrite the formula with the correct chemical symbols and the correct ratio of atoms. The correct formula of silver oxide is \(\mathrm{Ag}_{2}\mathrm{O}\). b. sodium sulfide, \(\mathrm{Na}_{2} \mathrm{S}\)

Identify the error

In this case, the formula has the correct chemical symbols and the correct ratio of atoms.

Confirm the formula

No changes are needed; the given formula is correct. Sodium sulfide remains \(\mathrm{Na}_{2}\mathrm{S}\). c. barium oxide, \(\mathrm{B}_{2} \mathrm{O}_{3}\)

Identify the error

Deconstruct the formula to find its individual elements. We have boron (B) and oxygen (O) instead of barium (Ba) and oxygen (O). The ratio of atoms is also incorrect.

Correct the formula

Rewrite the formula with the correct chemical symbols and the correct ratio of atoms. The correct formula of barium oxide is \(\mathrm{BaO}\). d. calcium nitride, \(\mathrm{Ca}_{3} \mathrm{N}_{2}\)

Identify the error

In this case, the formula has the correct chemical symbols and the correct ratio of atoms.

Confirm the formula

No changes are needed; the given formula is correct. Calcium nitride remains \(\mathrm{Ca}_{3} \mathrm{N}_{2}\). e. lithium bromide, \(\mathrm{Li}_{3} \mathrm{B}\)

Identify the error

Deconstruct the formula to find its individual elements. We have lithium (Li) and boron (B) instead of lithium (Li) and bromine (Br). The ratio of atoms is also incorrect.

Correct the formula

Rewrite the formula with the correct chemical symbols and the correct ratio of atoms. The correct formula of lithium bromide is \(\mathrm{LiBr}\).

Key concepts

Chemical Nomenclature

Understanding chemical nomenclature, the system for naming chemical compounds, is fundamental for anyone studying chemistry. Nomenclature involves not only knowing the names of the elements but also the rules for combining these names to describe compounds. Simple binary compounds consist of only two elements. The name of such a compound generally starts with the name of the metal (or the positive ion), followed by the name of the nonmetal (or negative ion) with its ending changed to -ide. In our exercise example, 'silver oxide' correctly combines 'silver' (the metal) with 'oxide', which hints at oxygen being the nonmetal.

There are also prefixes used to indicate the number of atoms of each element in compounds that are not binary. When dealing with multi-valent metals, which can form more than one type of positive ion, a roman numeral or the suffixes -ous and -ic can indicate the charge of the metal ion. For example, iron(II) oxide indicates that iron has a +2 charge. To master chemical nomenclature, students should familiarize themselves with the periodic table's groups, as elements within the same group typically form ions of the same charge, and memorize common polyatomic ions and their charges.

Chemical Compound Identification

Identifying chemical compounds requires a clear understanding of the elements that compose them and their respective ratios. When given a compound's name, such as 'barium oxide', one must know that the symbol for barium is 'Ba' and that for oxygen is 'O'. Besides just knowing the symbols, one must also identify the correct ratio of these elements to write the proper formula. The ratio often depends on the charge of the ions formed by the elements. Barium, a group 2 element, forms a +2 ion, while oxygen, in group 16, typically forms a -2 ion. Thus, they combine in a one-to-one ratio to form 'BaO'.

Incorrect identification of elements, like confusing boron (B) with barium (Ba), leads to incorrect chemical formulas. The exercise provided clearly demonstrates these pitfalls in compound identification. One helpful strategy is to use a chart of common charges for metal and nonmetal ions to cross-check formulas. This cross-checking supports correct identification and underscores the importance of understanding periodic trends and charge balance in compounds.

Writing Chemical Formulas

Writing chemical formulas involves several steps. First, you need to recognize the symbol for each element in the compound. Then, you must determine the valence, or combining capacity, of each element to know how many atoms of each are needed to balance the charges. The exercise demonstrates the importance of using the correct symbols and knowing the valences to properly write the formulas. For instance, silver has a +1 charge, meaning that two silver ions will combine with one -2 charged oxide ion to form 'Ag₂O', the proper formula for silver oxide.

In compounds like 'lithium bromide', it is crucial to know that the symbol for bromine is 'Br', not 'B', which stands for boron, and that lithium has a +1 charge while bromine has a -1 charge, showing that they combine in a one-to-one ratio, resulting in the formula 'LiBr'. Understanding these underlying principles is key to writing the correct chemical formulas. Moreover, practicing with different types of compounds, including polyatomic ions, will improve this skill and help avoid common mistakes.