Chemical Compounds and Their Formation

Hydrogen, Oxygen, and Water: Properties and Formation

Chemical compounds are formed when two or more elements combine in fixed, definite proportions, resulting in new substances with distinct properties. Water (H2O) is a classic example, formed from hydrogen and oxygen gases.

• Formation Equation:

• Properties Comparison: Water has very different physical and chemical properties compared to its constituent elements.

Types of Chemical Bonds

Chemical Bonding: Ionic, Covalent, and Metallic Bonds

Chemical bonds are forces that hold atoms together in compounds, lowering their potential energy and often achieving a noble-gas electron configuration.

• Ionic Bonds: Formed by electrostatic attraction between ions (metal + nonmetal), resulting in a lattice structure.

• Covalent Bonds: Formed by sharing electrons between nonmetals, resulting in molecules.

• Metallic Bonds: Bonded to several neighboring atoms, electrons are delocalized.

Lewis symbols represent valence electrons as dots around element symbols.

Representing Compounds: Chemical Formulas and Molecular Models

Types of Chemical Formulas

Chemical formulas indicate the elements present and their ratios in a compound.

• Empirical Formula: Shows the simplest whole-number ratio of atoms.

• Molecular Formula: Shows the actual number of atoms of each element in a molecule.

• Structural Formula: Uses lines to represent covalent bonds and shows how atoms are connected.

Molecular Models

Molecular models help visualize the geometry and bonding in molecules.

• Ball-and-stick model: Shows atoms as spheres and bonds as sticks.

• Space-filling model: Shows the relative sizes and spatial arrangement of atoms.

The Lewis Model and Octet Rule

Lewis Structures and the Octet Rule

Lewis structures use dots to represent valence electrons. The octet rule states that atoms tend to gain, lose, or share electrons to achieve eight valence electrons, mimicking noble gas configurations.

• Octet Rule: Applies to most main group elements.

• Duet Rule: Applies to hydrogen and helium (two electrons).

Ionic Bonding: The Lewis Model and Lattice Energies

Formation and Properties of Ionic Compounds

Ionic compounds are formed by the transfer of electrons from metals to nonmetals, resulting in cations and anions arranged in a lattice.

• Lattice Energy: The energy required to separate a mole of an ionic solid into gaseous ions. High lattice energy indicates strong ionic bonding.

• Properties: High melting/boiling points, non-conductive as solids, conductive in aqueous solution.

Ionic Compounds: Formulas and Names

Writing and Naming Ionic Compounds

Ionic compounds contain positive (cation) and negative (anion) ions. The formula reflects the smallest whole-number ratio of ions, and the sum of charges must equal zero.

• Binary Ionic Compounds: Metal + nonmetal. Name: cation name + anion base name + '-ide'.

• Metals with Invariant Charge: Do not specify charge (e.g., Na+, Ca2+).

• Metals with Variable Charge: Specify charge with Roman numerals (e.g., Fe(II), Cu(I)).

Polyatomic Ions and Oxyanions

Polyatomic ions are composed of two or more atoms. Oxyanions contain oxygen and another element, with naming conventions based on the number of oxygens.

• -ate: Most common oxyanion (e.g., nitrate NO3-).

• -ite: One oxygen less (e.g., nitrite NO2-).

• hypo- ... -ite: Two oxygens less.

• per- ... -ate: One oxygen more.

Hydrated Ionic Compounds

Hydrates are ionic compounds containing a specific number of water molecules per formula unit. Naming includes prefixes for the number of waters (e.g., pentahydrate).

• Example: CuSO4·5H2O is copper(II) sulfate pentahydrate.

Covalent Bonding: Simple Lewis Structures

Covalent Bonds and Multiple Bonds

Covalent bonds are formed by sharing pairs of electrons between atoms. Single, double, and triple bonds correspond to one, two, or three shared pairs, respectively.

• Single Bond: One pair shared (e.g., H2).

• Double Bond: Two pairs shared (e.g., O=C=O in CO2).

• Triple Bond: Three pairs shared (e.g., N≡N in N2).

• Bond Length: Decreases as the number of shared pairs increases.

Molecular Compounds: Formulas and Names

Naming Molecular Compounds

Molecular compounds are composed of two or more nonmetals. Naming uses prefixes to indicate the number of atoms.

• Prefixes: mono-, di-, tri-, tetra-, penta-, etc.

• Example: N2O is dinitrogen monoxide.

Formula Mass and the Mole Concept for Compounds

Calculating Formula Mass and Molar Mass

The formula mass is the sum of atomic masses of all atoms in a chemical formula. Molar mass is the mass in grams of one mole of a compound, numerically equivalent to its formula mass.

• Formula Mass Example: CO2:

• Molar Mass Example: Ca(NO3)2:

Using Molar Mass for Conversions

Molar mass is used as a conversion factor between grams and moles.

• Example: How many molecules of CO2 in 10.800 g?

Composition of Compounds

Mass Percent Composition

Mass percent composition expresses the percentage by mass of each element in a compound.

• Formula:

• Example: Ca(NO3)2: Ca = 24.42%, N = 17.07%, O = 58.50%

Conversion Factors from Chemical Formulas

Subscript numbers in chemical formulas represent mole ratios, useful for stoichiometric calculations.

• Example: 1 mole of CCl2F2 contains 2 moles of Cl.

Determining a Chemical Formula from Experimental Data

Empirical and Molecular Formulas

Empirical formulas are calculated from mass composition, and molecular formulas are whole-number multiples of empirical formulas.

• Empirical Formula Calculation: Divide moles of each element by the smallest value to get ratios.

• Molecular Formula Calculation:

Combustion Analysis

Combustion analysis is used to determine the empirical formula of organic compounds by measuring the masses of CO2 and H2O produced.

Organic Compounds

Organic vs. Inorganic Compounds

Organic compounds originate from living organisms and are mainly composed of carbon and hydrogen, sometimes with oxygen, nitrogen, or sulfur. Inorganic compounds originate from the Earth.

• Examples of Organic Compounds: Methane (CH4), Ethanol (C2H5OH)

• Examples of Inorganic Compounds: NaCl, NaHCO3

Alkanes and Alcohols

Alkanes have the general formula CnH2n+2, while alcohols have CnH2n+1OH.

Isomers and Functional Groups

Isomers are compounds with the same formula but different structures. Functional groups are specific groups of atoms within molecules that determine their chemical properties.

• Examples: 1-pentanol, 2-pentanol, 3-pentanol (isomers); carboxylic acid group (COOH), ether group (O).