Difficulty: Introductory | Prerequisites: Molecular Structure Representations (first set of Ch. 1 notes), basic knowledge of ions, metals vs. nonmetals
This section rounds out Chapter 1 by covering the classification and naming of inorganic compounds (binary compounds, acids, polyatomic ions) and then pivoting to organic compound types (hydrocarbons, functional groups). It bridges general chemistry terminology with the organic focus of the rest of the course. You should already know the difference between metals and nonmetals, and be comfortable with the formula types from the previous set of notes.
Chemistry sorts compounds into inorganic (binary ionic and molecular compounds, acids, polyatomic-ion compounds) and organic (carbon-based, starting with hydrocarbons). Within organic compounds, functional groups like hydroxyl (–OH) and carboxyl (–COOH) determine the compound's chemical behaviour and help with naming. Knowing the classification rules lets you predict properties and write correct names.
Binary compound
A compound formed from exactly two elements. When one element is a metal and the other a nonmetal, the result is an ionic compound. When both are nonmetals, the result is a molecular (covalent) compound.
Think of it as the simplest kind of compound: just two players on the field.
Ionic compound
A compound held together by the electrostatic attraction between cations (positive ions) and anions (negative ions), producing a net-neutral formula unit (e.g. BaBr₂).
In simple terms, a metal hands electrons to a nonmetal, and the opposite charges hold them together.
Molecular compound
A compound formed by two nonmetals sharing electrons through covalent bonds (e.g. N₂O₄, dinitrogen tetroxide). The element with the more positive oxidation state is written first.
Think of it as atoms cooperating rather than one giving and one taking.
Binary acid
An acid formed when hydrogen bonds with a nonmetal in a binary compound (e.g. HBr, hydrobromic acid). Named with the prefix "hydro-" and the suffix "-ic acid."
In simple terms, it is the simplest type of acid: hydrogen plus one other element.
Polyatomic ion
An ion consisting of two or more atoms joined by covalent bonds that carries an overall charge (e.g. NH₄⁺, MnO₄⁻). Most common polyatomic ions are anions.
Think of it as a group of atoms that travels together and acts as a single charged unit.
Oxyacid
An acid that contains hydrogen, oxygen, and one other element (e.g. HNO₃, nitric acid).
In simple terms, it is an acid where oxygen is part of the package.
Hydrate
A compound that has water molecules physically bonded into its crystal structure, written with a centred dot (e.g. CoCl₂·6H₂O).
Think of it as a compound that has trapped water inside its solid form.
Hydrocarbon
A compound consisting entirely of carbon and hydrogen atoms.
In simple terms, hydrocarbons are the backbone molecules of organic chemistry, and everything else is built by swapping some of their H atoms for other groups.
Alkane
A hydrocarbon containing only single bonds between carbon atoms (e.g. methane, CH₄; propane, C₃H₈).
Think of it as the fully "saturated" hydrocarbon: every carbon holds as many hydrogens as it can.
Alkene
A hydrocarbon containing at least one carbon-carbon double bond (e.g. ethene, C₂H₄).
In simple terms, a double bond means two fewer hydrogen atoms than the equivalent alkane, and the molecule is more reactive at that double-bond site.
Functional group
A specific grouping of atoms within an organic molecule that determines its chemical properties and reactivity. Compounds with the same functional group tend to behave similarly.
Think of it as a molecular "badge" that tells you how the compound will react.
Hydroxyl group (–OH)
The functional group characteristic of alcohols. Compounds ending in –OH are classified as alcohols (e.g. butanol).
Carboxyl group (–COOH)
The functional group characteristic of carboxylic acids. It consists of a carbonyl (C=O) bonded to a hydroxyl (–OH). Compounds ending in –COOH are carboxylic acids (e.g. acetic acid, oxalic acid).
Inorganic compounds are typically not of biological origin, and their atoms are connected using ionic bonds.
Binary compounds (metal + nonmetal)
The result is an ionic compound with a net-neutral charge (cation + anion).
For transition metals, specify the charge in the name (e.g. Iron(III) chloride).
Example: Barium Bromide, BaBr₂.
Binary compounds (nonmetal + nonmetal)
The result is a molecular (covalent) compound.
The element with a positive oxidation state is written first.
Greek prefixes indicate the number of each atom (di-, tri-, tetra-, etc.).
Example: Dinitrogen Tetroxide, N₂O₄.
Binary acids
Formed when hydrogen bonds with a nonmetal.
Named with "hydro-" prefix and "-ic acid" suffix.
Exception: NH₃ is a base (ammonia), not an acid, even though it contains H bonded to a nonmetal.
Example: Hydrobromic Acid, HBr.
Polyatomic ions
Two or more atoms connected by covalent bonds that carry an overall charge.
Most common polyatomic ions are anions (e.g. permanganate, MnO₄⁻).
The ammonium ion (NH₄⁺) is a notable cation.
When a polyatomic ion bonds to a metal via ionic bonds, the result is a chemical compound (e.g. Sodium Permanganate, NaMnO₄).
Oxyacids
Contain hydrogen, oxygen, and one other element.
Example: Nitric Acid, HNO₃.
Complex compounds and hydrates
Some compounds can appear in multiple written forms yet represent the same substance.
Hydrates have water molecules bonded into the crystal structure.
Written with a centred dot: CoCl₂·6H₂O.
Hydrocarbons
Compounds consisting of only carbon and hydrogen atoms.
Subcategories are defined by bond type:
Alkanes: only single bonds (e.g. methane, CH₄; propane, C₃H₈).
Alkenes: one or more double bonds (e.g. ethene, C₂H₄).
Alkynes (mentioned for completeness): one or more triple bonds.
Functional groups
Atoms or groups of atoms connected to chains or rings of organic molecules that determine the compound's behaviour.
Compounds with the same functional group tend to share similar properties.
Functional groups also help with nomenclature (naming).
Key groups from this chapter:
Hydroxyl group (–OH): defines alcohols (e.g. butanol).
Carboxyl group (–COOH): defines carboxylic acids (e.g. acetic acid, oxalic acid).
Category | Compound | Formula |
|---|---|---|
Binary ionic | Barium Bromide | BaBr₂ |
Binary molecular | Dinitrogen Tetroxide | N₂O₄ |
Binary acid | Hydrobromic Acid | HBr |
Polyatomic-ion compound | Sodium Permanganate | NaMnO₄ |
Oxyacid | Nitric Acid | HNO₃ |
Hydrate | Cobalt(II) Chloride Hexahydrate | CoCl₂·6H₂O |
Alkane | Methane | CH₄ |
Alkene | Ethene | C₂H₄ |
Functional Group | Ending | Compound Class | Example |
|---|---|---|---|
Hydroxyl | –OH | Alcohols | Butanol |
Carboxyl | –COOH | Carboxylic acids | Acetic acid, Oxalic acid |
Binary acids and oxyacids appear constantly in laboratory and industrial settings. Hydrochloric acid (HCl, a binary acid) is used in steel pickling and food processing; nitric acid (HNO₃, an oxyacid) is a key ingredient in fertiliser manufacturing.
Functional groups are the reason different organic molecules smell, taste, and react differently. The carboxyl group is what makes vinegar sour (acetic acid); the hydroxyl group is what makes ethanol a liquid you can drink rather than a gas.
Students often think any compound containing hydrogen is an acid. It is not. NH₃ (ammonia) contains hydrogen bonded to a nonmetal yet is a base.
Students mix up ionic and molecular binary compounds. The key distinction: metal + nonmetal = ionic; nonmetal + nonmetal = molecular.
Students sometimes assume the carboxyl group (–COOH) is just a hydroxyl group (–OH) attached to a carbonyl. While that is structurally true, the carboxyl group behaves as a single functional unit and makes the molecule an acid, not an alcohol.
Students forget that hydrate formulas use a centred dot (·) to separate the main compound from the water of crystallisation. Writing CoCl₂6H₂O without the dot is incorrect notation.
⚠️ Classifying a compound as organic or inorganic based on its formula (look for C–H bonds) is a standard exam question.
⚠️ Naming binary compounds: know the rules for ionic vs. molecular naming (Roman numerals for transition-metal charges; Greek prefixes for molecular compounds).
⚠️ Identifying functional groups from a condensed or line-angle formula appears on nearly every organic chemistry exam from this point onward.
⚠️ The NH₃ exception (base, not acid) is a classic trick question in the binary-acids section.
True or False: A binary compound made from two nonmetals is ionic.
False. Two nonmetals form a molecular (covalent) compound.
Fill in the blank: An oxyacid always contains hydrogen, oxygen, and ______.
One other element.
True or False: The hydroxyl group (–OH) makes a compound a carboxylic acid.
False. The hydroxyl group defines an alcohol. The carboxyl group (–COOH) defines a carboxylic acid.
Fill in the blank: Alkanes contain only ______ bonds between carbon atoms.
Single.
True or False: NH₃ is a binary acid.
False. NH₃ is a base (ammonia).
Q: Which of the following formulas are organic: HClO, C₅H₁₀, CO₂?
A: C₅H₁₀ is organic because it contains carbon-hydrogen bonds. HClO is an oxyacid (inorganic). CO₂ contains carbon but no C–H bond, so it is classified as inorganic.
Q: Classify acetic acid, butanol, and oxalic acid into their appropriate functional groups.
A: Acetic acid has a carboxyl group (–COOH). Butanol has a hydroxyl group (–OH). Oxalic acid has two carboxyl groups.
Q: What is the name and molecular formula of a branched five-carbon alkane (methylbutane)?
A: Methylbutane (also called 2-methylbutane or isopentane). Its molecular formula is C₅H₁₂.
Q: A compound has the formula NaMnO₄. Is it ionic or covalent? Name it.
A: Ionic. The polyatomic ion permanganate (MnO₄⁻) is bonded to sodium (Na⁺) via ionic bonds. The name is Sodium Permanganate.
Q: Write the structural formula for propane.
A: H–C–C–C–H with three H on the first carbon, two H on the middle carbon, and three H on the last carbon: CH₃CH₂CH₃.
Functional groups are the organising principle for the rest of organic chemistry. Chapters on alcohols, ethers, aldehydes, ketones, and carboxylic acids each focus on one functional group's reactions. Recognising –OH vs. –COOH here sets you up for those chapters.
The inorganic naming conventions (binary, polyatomic, oxyacid) are revisited in general chemistry exams and appear whenever stoichiometry problems involve naming reactants or products.
Alkane and alkene classification leads directly into nomenclature (IUPAC naming rules, Chapter 2) and later into reaction mechanisms (addition reactions of alkenes, typically Chapter 7 or 8).
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