Compounds and Bonding

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms covalently bonded, carrying a net charge. Memorizing their names and formulas is essential for naming and writing chemical compounds.

• Common Polyatomic Ions: hydroxide (OH-), hydronium (H3O+), ammonium (NH4+), nitrate (NO3-), chlorate (ClO3-), carbonate (CO32-), cyanide (CN-), acetate (C2H3O2-), sulfate (SO42-), phosphate (PO43-).

• Application: Used in naming ionic compounds and understanding chemical reactions.

Naming Compounds

Chemical nomenclature follows systematic rules to ensure clarity and consistency.

• Ionic Compounds: Name the cation (metal or ammonium) first, then the anion. For transition metals, indicate the charge with Roman numerals.

• Covalent Compounds: Use prefixes to indicate the number of each atom (mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-). The more electronegative element is named last with the suffix "-ide."

• Organic Compounds: Use roots for 1-10 carbons (meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non-, dec-). Functional groups and substituents are named according to IUPAC rules.

VSEPR Geometries

The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular shapes based on electron pair repulsion around a central atom.

• Electron Density Regions: 2-6 regions lead to different geometries (linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral).

• Bond Angles: Linear (180°), trigonal planar (120°), tetrahedral (109.5°), trigonal bipyramidal (90°, 120°, 180°), octahedral (90°, 180°).

• Special Focus: Carbon, nitrogen, and oxygen form characteristic geometries based on their bonding and lone pairs.

Line Diagrams and Lewis Structures

Line diagrams (skeletal structures) and Lewis structures are two ways to represent molecules. Line diagrams omit hydrogen atoms bonded to carbon for simplicity, while Lewis structures show all atoms and valence electrons.

• Interpretation: Each line represents a bond; vertices and line ends represent carbon atoms.

Functional Groups

Functional groups are specific groups of atoms within molecules that determine chemical reactivity and properties.

• Common Functional Groups: alkane, alkene, alkyne, aromatic, alcohol, phenol, ether, aldehyde, ketone, carboxylic acid, carboxylate, ester, amine, amide, thiol, thioether, disulfide, phosphate.

• Note: Alkanes are not functional groups but are the simplest organic compounds.

Bond Types and Properties

The type of bond (single, double, triple) affects bond length, strength, and reactivity.

• Single Bonds: Longest and weakest; most flexible.

• Double Bonds: Shorter and stronger than single bonds; less flexible.

• Triple Bonds: Shortest and strongest; least flexible and most reactive.

Isomerism

Isomers are compounds with the same molecular formula but different structures or spatial arrangements.

• Types: Structural (skeletal/constitutional), stereoisomers (geometric, optical), conformational, enantiomers.

• Example: Butane and isobutane are structural isomers.

Chapter 3: Electrons, Ionic Compounds, and Molecular Polarity

Energy Levels and Valence Electrons

Electrons occupy energy levels (shells) around the nucleus. The outermost electrons are called valence electrons and determine chemical reactivity.

• Valence Shell: The outermost electron shell.

• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.

Ion Formation

Atoms form ions by gaining or losing electrons. Metals lose electrons to form cations; non-metals gain electrons to form anions.

• Isoelectronic: Ions with the same electron configuration as a noble gas.

Naming and Writing Ionic Compounds

• Formula: Combine cations and anions in ratios that yield a neutral compound.

• Naming: Name the cation first, then the anion (with "-ide" or polyatomic name).

Covalent Bond Formation and Lewis Structures

Covalent bonds form when atoms share electrons. Lewis structures depict the arrangement of atoms and shared electron pairs.

• Example: Water (H2O) has two single bonds and two lone pairs on oxygen.

Mole Concept and Molar Mass

The mole is a counting unit for atoms, molecules, or ions. Molar mass is the mass of one mole of a substance, calculated from its chemical formula.

• Formula:

Molecular Shape and Polarity

The shape of a molecule (molecular geometry) and the distribution of electrons determine whether a molecule is polar or nonpolar.

• Polar Bonds: Formed when atoms have different electronegativities.

• Polarity of Molecules: Determined by both bond polarity and molecular shape.

Chapter 4: Organic Molecules and Isomerism

Structural Representations

Organic molecules can be represented in several ways:

• Condensed Structures: Show all atoms but group similar ones together.

• Lewis Structures: Show all atoms and bonds, including lone pairs.

• Skeletal (Line) Diagrams: Simplified, showing only carbon skeleton and functional groups.

Saturated vs. Unsaturated Hydrocarbons

Saturated hydrocarbons contain only single bonds; unsaturated hydrocarbons contain double or triple bonds or rings.

• Index of Hydrogen Deficiency (IHD): Indicates the number of rings and/or pi bonds.

• Formula: (where C = carbons, N = nitrogens, H = hydrogens, X = halogens)

Bond Types in Hydrocarbons

• Single Bond: 1 sigma bond

• Double Bond: 1 sigma + 1 pi bond

• Triple Bond: 1 sigma + 2 pi bonds

Resonance

Resonance involves the delocalization of electrons across multiple atoms, increasing molecular stability.

• Example: Benzene ring (C6H6)

General Formulas of Hydrocarbons

• Alkanes:

• Alkenes:

• Alkynes:

• Cycloalkanes:

Properties and Nomenclature

• Alkanes: Recognize the longest carbon chain; name alkyl and halogen substituents.

• Cycloalkanes: 5- and 6-membered rings are most common in nature.

• Haloalkanes: Alkanes with halogen substituents.

Intermolecular Forces (IMF) and Fatty Acids

IMF influence the state of matter and properties of fatty acids. Saturated fatty acids have higher melting points due to stronger IMFs.

Classification of Functional Groups

• Alcohols and Amines: Classified as 1°, 2°, 3°, or 4° based on the number of carbon groups attached to the functional atom (O or N).

Isomer Relationships

• Structural Isomers: Differ in connectivity.

• Stereoisomers: Same connectivity, different spatial arrangement (includes geometric and optical isomers).

• Conformational Isomers: Differ by rotation around single bonds.

• Geometric Isomers: Cis/trans isomers in alkenes and cycloalkanes.

• Optical Isomers (Enantiomers): Non-superimposable mirror images; have chiral centers.

Cis/Trans Isomerism

Cis/trans isomerism occurs in alkenes and cycloalkanes when two different groups are attached to each carbon of a double bond or ring. If two groups on the same carbon are identical, cis/trans isomerism is not possible.

• Chiral Centers: Carbon atoms bonded to four different groups.

Table: Common Polyatomic Ions

Table: Prefixes and Roots for Naming Compounds

Additional info: Some explanations and formulas have been expanded for clarity and completeness, including the Index of Hydrogen Deficiency and the classification of isomers.