BackGOB Chemistry Study Guide: Ionic and Covalent Compounds, Molecular Structure, and Organic Nomenclature
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Chapter 3.3: Ionic Compounds
Definition and Properties of Ionic Bonds
An ionic bond is a type of chemical bond formed through the electrostatic attraction between oppositely charged ions, typically a metal cation and a nonmetal anion.
Ions are atoms or molecules that have gained or lost electrons, resulting in a net charge.
Metals tend to lose electrons to form cations (positively charged), while nonmetals gain electrons to form anions (negatively charged).
Example: Sodium chloride (NaCl) forms when Na+ and Cl- ions combine.
Naming Ionic Compounds
To name an ionic compound from its formula, name the cation first, followed by the anion.
For main group elements, the cation uses the element name; the anion uses the root of the element plus "-ide" (e.g., NaCl is sodium chloride).
For transition metals with variable charge, use Roman numerals to indicate the charge (e.g., FeCl2 is iron(II) chloride).
Polyatomic ions retain their special names (e.g., NaNO3 is sodium nitrate).
Determining Ions and Formulas
Given a compound's name or formula, identify the ions present by considering the charges needed for neutrality.
To write a formula from ions, balance the total positive and negative charges so the compound is neutral.
Example: To form magnesium chloride, combine Mg2+ and Cl- ions: .
Naming Rules and Variable Charges
Main group elements usually have fixed charges; transition metals may have variable charges.
Roman numerals are used for elements with variable charge (e.g., copper(II) sulfate).
Polyatomic ions (e.g., SO42-, NO3-) have specific names and formulas.
Lab #3: Double Replacement and Precipitation Reactions
Predicting Products and Balancing Equations
In a double replacement reaction, two ionic compounds exchange ions to form two new compounds.
Precipitation occurs if one product is insoluble in water.
Use solubility rules to predict if a precipitate forms.
Balance the chemical equation to ensure the same number of each atom on both sides.
Phase Labels
(aq) indicates an aqueous (dissolved) species; (s) indicates a solid (precipitate).
Example:
Chapter 3.4: Covalent Compounds and Lewis Structures
Covalent Bonds and Compounds
A covalent bond is formed when two nonmetal atoms share electrons.
Covalent compounds consist of molecules with shared electron pairs.
Example: Water (H2O) is a covalent compound.
Bonding and Valence Electrons
The number of bonds an element forms is often determined by its number of valence electrons.
Example: Carbon (4 valence electrons) typically forms 4 bonds.
Lewis Structures
Lewis structures show the arrangement of valence electrons among atoms in a molecule.
Steps:
Count total valence electrons.
Arrange atoms and connect with single bonds.
Distribute remaining electrons to satisfy octet/duet rules.
Bonding pairs are shared between atoms; nonbonding (lone) pairs are not shared.
Naming Binary Molecular Compounds
Use prefixes to indicate the number of each atom (mono-, di-, tri-, etc.).
The more electronegative element is named last with the "-ide" suffix.
Example: CO2 is carbon dioxide.
Chapter 3.5: The Mole and Molar Mass
Avogadro's Number and the Mole
The mole is a counting unit for atoms, molecules, or ions: particles.
Used to relate mass, number of particles, and chemical amounts.
Molar Mass
Molar mass is the mass of one mole of a substance, in grams per mole (g/mol).
Calculated by summing the atomic masses of all atoms in a formula.
Example: has a molar mass of .
Chapter 3.6: Molecular Geometry and Charge Clouds
Charge Clouds and Electron Geometry
A charge cloud is a region where electrons are likely to be found, including bonding and nonbonding pairs.
Bonding charge clouds are shared between atoms; nonbonding charge clouds are lone pairs.
Electron geometry is determined by the number of charge clouds around a central atom.
Common Electron Geometries
Name | Number of Charge Clouds | Shape |
|---|---|---|
Linear | 2 | Straight line |
Trigonal Planar | 3 | Flat triangle |
Tetrahedral | 4 | Pyramid with triangular base |
Lone pairs can alter bond angles, making them smaller than ideal values.
Chapter 3.7: Electronegativity and Polarity
Electronegativity and Bond Polarity
Electronegativity is the ability of an atom to attract shared electrons in a bond.
Increases across a period and decreases down a group on the periodic table.
Polar covalent bonds have unequal sharing of electrons; nonpolar covalent bonds have equal sharing.
Use dipole arrows (→) or δ+/δ- symbols to indicate bond polarity.
Molecular polarity depends on both bond polarity and molecular geometry.
Chapter 4.1: Organic Structures
Types of Structural Representations
Condensed structure: Shows atoms in a group (e.g., CH3CH2OH).
Lewis structure: Shows all atoms, bonds, and lone pairs.
Skeletal structure: Lines represent bonds; carbon atoms are implied at line ends and vertices.
Be able to convert between these representations.
Chapter 4.2: Hydrocarbons and Alkanes
Hydrocarbons are organic compounds containing only carbon and hydrogen.
Alkanes are saturated hydrocarbons with only single bonds (general formula: ).
Chapter 4.3: Functional Groups
Recognizing Functional Groups
Functional Group | Example |
|---|---|
Alkane | CH4 |
Alkene | CH2=CH2 |
Alkyne | HC≡CH |
Aromatic | Benzene ring |
Phenol | Benzene ring with OH |
Alcohol | CH3OH |
Ether | CH3OCH3 |
Amine | CH3NH2 |
Alkyl halide | CH3Cl |
Carboxylic acid | CH3COOH |
Ester | CH3COOCH3 |
Amide | CH3CONH2 |
Chapter 4.4: IUPAC Nomenclature of Alkanes
Naming and Drawing Alkanes
Apply IUPAC rules to name straight-chain alkanes and those with substituents.
Label alkyl substituents (e.g., methyl, ethyl) and assign the lowest possible numbers to substituents.
Construct complete IUPAC names from structures and draw structures from names.
Example: 2-methylpropane (isobutane).
