Binary Compounds of Metals and Nonmetals

When a metal combines with a nonmetal, they form an ionic compound. These compounds must be electrically neutral, with the simplest combination of ions making up the formula.

Learning the common ions is essential for naming these compounds:

• Group 1 metals (Li, Na, K, Rb, Cs) form +1 cations
• Group 2 metals (Mg, Ca, Sr, Ba) form +2 cations
• Transition metals often form multiple ions with different charges (like iron(II) ion Fe²⁺ and iron(III) ion Fe³⁺)

For nonmetals, common anions include:

• Halides: fluoride (F⁻), chloride (Cl⁻), bromide (Br⁻), iodide (I⁻)
• Others: oxide (O²⁻), sulfide (S²⁻), nitride (N³⁻)

💡 When writing formulas, you don't need to memorize every combination! If you know the charges of the ions, you can determine how many of each ion are needed to create a neutral compound.

With these ions, you can predict compounds like silver bromide (AgBr), calcium fluoride (CaF₂), and aluminum oxide (Al₂O₃).

Polyatomic Ions

Polyatomic ions consist of two or more atoms bonded together that carry a charge. Many contain oxygen and are called oxoanions.

Some key polyatomic ions to know:

• Positive ions: ammonium (NH₄⁺) and hydronium (H₃O⁺)
• Negative ions: hydroxide (OH⁻), nitrate (NO₃⁻), carbonate (CO₃²⁻), phosphate (PO₄³⁻), and sulfate (SO₄²⁻)

Look for patterns in naming to help memorization:

• "-ate" endings generally have more oxygen than "-ite" endings
• "hydrogen" or "bi-" prefixes indicate a hydrogen has replaced one negative charge

When naming compounds with polyatomic ions, follow the same rules as with simple ions. For example:

• Sodium sulfate is Na₂SO₄
• Potassium hydrogen carbonate is KHCO₃
• Iron(III) nitrate is Fe(NO₃)₃

🔑 An acid is a substance that produces H⁺ ions in aqueous solution, while a salt is an ionic compound where an acid's hydrogen has been replaced by another positive ion.

Understanding polyatomic ions is crucial for naming the compounds they form and for predicting their chemical behavior.

Acids

Acids fall into two main categories: binary acids and oxoacids. Both produce H⁺ ions in water.

Binary acids contain hydrogen and one other nonmetal. When dissolved in water, they're named with the prefix "hydro-" and suffix "-ic acid":

• HCl: hydrogen chloride (pure) → hydrochloric acid (in water)
• HBr: hydrogen bromide → hydrobromic acid
• H₂S: hydrogen sulfide → hydrosulfuric acid

Oxoacids contain hydrogen, oxygen, and another nonmetal. Their names relate to their corresponding oxoanions:

• Acids ending in "-ic" contain oxoanions ending in "-ate" (HNO₃ is nitric acid; its ion is nitrate, NO₃⁻)
• Acids ending in "-ous" contain oxoanions ending in "-ite" (HNO₂ is nitrous acid; its ion is nitrite, NO₂⁻)

⚠️ You must memorize the six strong acids: HCl, HBr, HI, HNO₃, H₂SO₄, and HClO₄. All other acids are weak, meaning they don't fully dissociate in water.

Similarly, there are nine strong bases to memorize: LiOH, NaOH, KOH, RbOH, CsOH, Mg(OH)₂, Ca(OH)₂, Sr(OH)₂, and Ba(OH)₂. All others are weak.

Binary Compounds of Two Nonmetals

When two nonmetals combine, they form molecular compounds. These are named using numerical prefixes to show how many atoms of each element are present:

For example:

• SO₂ is sulfur dioxide (one sulfur, two oxygens)
• Cl₂O₇ is dichlorine heptoxide (two chlorines, seven oxygens)

Sometimes oxidation numbers are used instead of prefixes. For example, P₂O₅ might be called phosphorus(V) oxide instead of diphosphorus pentoxide.

Simple Organic Nomenclature

Organic compounds are based on carbon chains with various functional groups. Their names combine:

1. A prefix indicating the number of carbons $meth- = 1, eth- = 2, prop- = 3, etc.$
2. A suffix showing the functional group $-ane = alkane, -ene = alkene, -yne = alkyne, etc.$

🔍 For the AP exam, focus on identifying the structure from the name. You'll typically deal with chains of no more than 6 carbons.

Some examples:

• Ethane (C₂H₆): Two carbons with single bonds
• Propene (C₃H₆): Three carbons with a double bond
• Ethanol (C₂H₅OH): Two carbons with an -OH group

Cyclic Compounds and Structural Variations

Organic compounds can form rings by adding the prefix "cyclo-" to the name. Ring structures have two fewer hydrogens than their straight-chain counterparts:

• Cyclohexane (C₆H₁₂): A six-carbon ring with single bonds
• Cyclohexene (C₆H₁₀): A six-carbon ring with one double bond
• Benzene (C₆H₆): A special six-carbon aromatic ring with alternating double bonds

When drawing organic structures, remember that each carbon needs four bonds total. If you see a carbon with fewer connections shown, add hydrogens until it has four bonds.

For functional groups, numbers indicate their position on the carbon chain. For example:

• 1-propanol has the -OH group on the first carbon
• 2-propylamine has the -NH₂ group on the second carbon

💡 When taking the AP exam, focus on understanding the overall structure rather than worrying about minor naming details. If you recognize the functional group and carbon chain, you can usually determine the correct formula.

The AP exam typically focuses on simple organic molecules, so mastering the basics of functional groups and carbon chains will be sufficient.

Functional Groups in Organic Chemistry

Each functional group gives organic compounds distinctive properties and reactivity. Here's how they appear in propane-based molecules:

Hydrocarbons:

• Propane (C₃H₈): All single bonds between carbons
• Propene (C₃H₆): Contains a carbon-carbon double bond
• Propyne (C₃H₄): Contains a carbon-carbon triple bond

Oxygen-containing compounds:

• 1-propanol (C₃H₇OH): Contains an -OH (hydroxyl) group on the first carbon
• Methoxyethane (CH₃OC₂H₅): Contains an -O- (ether) linkage between carbons
• Propanal (C₂H₅CHO): Contains a -CHO (aldehyde) group at the end
• Propanone (CH₃COCH₃): Contains a C=O (ketone) group in the middle (also known as acetone)
• Propanoic acid (C₂H₅COOH): Contains a -COOH (carboxylic acid) group

Nitrogen-containing compound:

• 2-propylamine (C₃H₇NH₂): Contains an -NH₂ (amine) group on the second carbon

🧪 When you encounter a complex organic name, break it down into its parts: first identify the main chain, then look for functional groups and their positions on the chain.

Remember that the functional group suffix takes priority in naming. The location of the functional group is indicated by a number prefix $like 1-propanol or 2-propylamine$.