Study Guide: Atomic Structure, Moles, and Chemical Nomenclature

Chapter 2: Atomic Structure and Moles

Nuclear Model of the Atom

The nuclear model describes the atom as a dense nucleus containing protons and neutrons, surrounded by electrons. Understanding atomic structure is fundamental to all of chemistry.

• Structure and Units: Atoms consist of a nucleus (protons and neutrons) and electrons in surrounding orbitals. Atomic mass is measured in atomic mass units (amu).

• Atomic Number (Z) and Mass Number (A): The atomic number is the number of protons in the nucleus, defining the element. The mass number is the sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons. Isotopes have the same atomic number but different mass numbers.

• Average Mass Calculations: The average atomic mass of an element is calculated based on the relative abundance and mass of its isotopes.

Example: Chlorine has two main isotopes: 35Cl and 37Cl. The average atomic mass is calculated using their natural abundances.

Moles and Molar Mass

The mole is a counting unit in chemistry, representing Avogadro's number ($6.022 \times 10^{23}$) of particles (atoms, molecules, ions).

• Mole Calculations: The number of moles ($n$) is calculated as $n = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$.

• Molar Mass: The mass of one mole of a substance, numerically equal to the average atomic or molecular mass in grams per mole.

Example: To find the number of moles in 18.0 g of water ($H_2O$): Molar mass of $H_2O = 2(1.01) + 16.00 = 18.02$ g/mol $\text{Moles} = \frac{18.0\ \text{g}}{18.02\ \text{g/mol}} = 1.00$ mol

Chapter 3: Chemical Compounds and Nomenclature

Compound Basics

Chemical compounds are formed by the combination of two or more elements. Compounds can be classified as ionic or covalent based on the nature of the bonding.

• Ionic Bonding: Involves the transfer of electrons from one atom to another, forming ions that are held together by electrostatic forces.

• Covalent Bonding: Involves the sharing of electron pairs between atoms.

Nomenclature

Nomenclature is the systematic method of naming chemical compounds.

• Ionic Compounds:

  • Monatomic Ions: Ions consisting of a single atom (e.g., Na+, Cl-).

  • Polyatomic Ions: Ions composed of two or more atoms covalently bonded (e.g., $\text{NO}_3^-$, $\text{SO}_4^{2-}$).

  • Oxoanions: Polyatomic ions containing oxygen (e.g., $\text{CO}_3^{2-}$, $\text{PO}_4^{3-}$).

  • Ions with Multiple Charges: Some elements form ions with different charges (e.g., Fe2+ and Fe3+).

• Molecular Compounds: Composed of nonmetals bonded covalently. Named using prefixes to indicate the number of each atom (e.g., CO2 is carbon dioxide).

• Acids: Compounds that release H+ ions in solution. Naming depends on the anion present (e.g., HCl is hydrochloric acid, H2SO4 is sulfuric acid).

Molecular Mass and Formula Mass

The molecular mass (for covalent compounds) or formula mass (for ionic compounds) is the sum of the atomic masses of all atoms in a molecule or formula unit.

• Compositions: The percent composition of an element in a compound is calculated as: $\text{Percent Composition} = \frac{\text{mass of element in 1 mol of compound}}{\text{molar mass of compound}} \times 100\%$

• Empirical and Molecular Formulas: The empirical formula gives the simplest whole-number ratio of atoms in a compound. The molecular formula gives the actual number of atoms of each element in a molecule.

Example: For glucose ($C_6H_{12}O_6$), the empirical formula is $CH_2O$.

Table: Types of Chemical Compounds and Their Naming

Type	Example	Naming Rule
Ionic (Monatomic)	NaCl	Metal + Nonmetal (e.g., sodium chloride)
Ionic (Polyatomic)	NaNO3	Metal + Polyatomic Ion (e.g., sodium nitrate)
Molecular	CO2	Prefix + Name of First Element + Prefix + Name of Second Element + -ide (e.g., carbon dioxide)
Acid (Binary)	HCl	Hydro- + base name of nonmetal + -ic acid (e.g., hydrochloric acid)
Acid (Oxoacid)	H2SO4	Base name of polyatomic ion + -ic or -ous acid (e.g., sulfuric acid)

Additional info: Chapter 4 is explicitly excluded from Exam 1. Focus your study on the listed topics from Chapters 2 and 3, as outlined above.