Molecular Compounds: Formulas and Nomenclature
Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular com…
Molecular compounds are formed by atoms of two or more nonmetallic elements via covalent bonds. However, the same elements may combine in different ratios, giving rise to different molecular compounds. Hence, each molecular compound is described using distinct chemical formulas and systematic naming based on the number of atoms of its constituent elements.
A binary molecular compound is represented by first indicating the more metal-like element situated to the left and bottom of the periodic table. The more nonmetallic element is denoted subsequently. Numerical subscripts signify the number of atoms of each element.
These binary molecular compounds are named using a format beginning with a Greek-prefix indicating the number of atoms of the first element, followed by the element name. The prefix 'mono-' is usually omitted for the first element.
A second Greek-prefix denotes the number of atoms of the second element, which is followed by the element base-name ending with the suffix ‘-ide'. Hence the two different molecular compounds of carbon and oxygen, CO2 and C2O, are named carbon dioxide and dicarbon monoxide, respectively.
Acids, which are hydrogen-containing molecular compounds that dissociate into hydrogen plus ions and anions in water, follow a similar nomenclature. The formula of acids denotes the hydrogen first, followed by the nonmetal elements. Acids can be categorized as binary acids or oxyacids, depending on their constituent elements.
Binary acids are composed of hydrogen and a nonmetal. The nomenclature uses the term ‘hydro', followed by the nonmetal base-name ending with the suffix ‘-ic’, and concludes with the term ‘acid’. The binary acid, HF, is named hydrofluoric acid.
Oxyacids, on the other hand, contain hydrogen and an oxyanion composed of a nonmetal and oxygen. The names of oxyacids depend on the ending-suffix in the oxyanion name. For oxyanions ending with ‘-ate’, the format uses the base-name of the oxyanion, followed by the suffix ‘-ic’, ending with the term ‘acid’. The oxyacid containing hydrogen-ions and acetate-ions is named acetic acid. For oxyanions ending with ‘-ite’, the format uses the base-name of the oxyanion, followed by the suffix ‘-ous’, ending with the term ‘acid’. The oxyacid containing hydrogen-ions and sulfite-ions is named sulfurous acid.
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Q1: How do you write the chemical formula for a binary molecular compound?
Binary molecular compounds are written by placing the more metal-like element first, followed by the more nonmetallic element. Numerical subscripts indicate the number of atoms of each element. For example, carbon and oxygen form CO and CO2, representing different compounds with distinct properties. The element positioned to the left and bottom of the periodic table is listed first.
Q2: What is the naming system for binary molecular compounds?
Binary molecular compounds use Greek prefixes to denote the number of atoms of each element. The first element name is preceded by a prefix, with 'mono-' typically omitted. The second element name ends with the suffix '-ide' and is also preceded by a prefix. For example, CO2 is carbon dioxide and N2O is dinitrogen monoxide.
Q3: How are binary acids named differently from other molecular compounds?
Binary acids contain hydrogen and one nonmetallic element. They are named using 'hydro-' followed by the nonmetal base-name ending with '-ic' and the word 'acid'. For instance, HF dissolved in water is called hydrofluoric acid. This naming convention reflects the acidic properties these compounds exhibit when dissolved in water.
Q4: What determines whether an oxyacid is named with '-ic' or '-ous' suffix?
The oxyacid naming depends on the oxyanion's ending suffix. If the oxyanion ends with '-ate', the oxyacid uses '-ic' before 'acid'. If the oxyanion ends with '-ite', the oxyacid uses '-ous' before 'acid'. For example, acetate ions form acetic acid, while sulfite ions form sulfurous acid.
Q5: Why do carbon and oxygen form two different compounds with different names?
Carbon and oxygen can combine in different ratios because covalent bonding allows significant variation in atom combination. CO and CO2 are distinct substances with different properties, so they require different names to avoid confusion. Greek prefixes explicitly identify these ratios: CO is carbon monoxide and CO2 is carbon dioxide.
Q6: What is the relationship between an element's periodic table position and molecular compound naming?
The periodic table position determines element order in molecular compound formulas and names. The more metal-like element, located to the left and bottom, is named first. The more nonmetallic element, positioned to the right and top, is named second with the '-ide' suffix. This systematic approach helps identify compound composition from its name.
Q7: How do oxyacids differ structurally from binary acids?
Binary acids contain only hydrogen and one nonmetallic element, while oxyacids contain hydrogen, oxygen, and at least one other element bonded as a polyatomic oxygen-containing ion. Oxyacids are formed from hydrogen combined with oxyanions, making their structure more complex than binary acids. Both types release hydrogen ions when dissolved in water.