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General Chemistry II: Atomic Structure, Periodic Trends, Bonding, Geometry, Nomenclature, and Electron Configurations – Study Guide & Practice Problems

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Atomic Structure & Orbitals

Subshells and Orbitals

Atoms consist of electrons arranged in shells, subshells, and orbitals. Understanding these arrangements is fundamental to predicting chemical behavior.

  • Principal Quantum Number (n): Indicates the main energy level or shell. For each value of n, there are n subshells.

  • Subshells: Each shell contains subshells labeled s, p, d, f, etc. The number of subshells in a shell equals n.

  • Orbitals: Each subshell contains a specific number of orbitals: s (1), p (3), d (5), f (7).

  • Valid Orbitals: Only certain combinations of n and l (azimuthal quantum number) are allowed. For example, 3f is not valid because f orbitals start at n=4.

  • Maximum Electrons in f Subshell: Each orbital holds 2 electrons. The f subshell has 7 orbitals, so it can hold electrons.

  • Lowest n for f Subshell: The f subshell first appears in the n=4 shell.

Example: For n=3, there are 3 subshells: 3s, 3p, and 3d.

Periodic Trends & Atomic Size

Atomic and Ionic Radii

Periodic trends describe how atomic properties change across the periodic table. Atomic size is influenced by nuclear charge and electron configuration.

  • Na vs. Na+: Na+ is smaller than Na because it has lost an electron, reducing electron-electron repulsion and increasing effective nuclear charge.

  • Cl vs. Br: Br is larger than Cl because atomic size increases down a group due to additional electron shells.

  • Order of Increasing Size (O2−, F−, Ne): O2− > F− > Ne. All have the same number of electrons (isoelectronic), but more protons pull electrons closer, making Ne smallest.

  • Smallest Atomic Radius (Li, C, F, Ne): Ne has the smallest atomic radius due to its high nuclear charge and full shell.

Additional info: Atomic radius generally decreases across a period and increases down a group.

Bonding & Polarity

Molecular Polarity and Lewis Structures

Chemical bonds and molecular shapes determine whether a molecule is polar or nonpolar.

  • Nonpolar Molecules: CO2 is nonpolar due to its linear geometry and equal bond dipoles. H2 is nonpolar (homonuclear diatomic). NH3 and SO2 are polar due to their shapes and electronegativity differences.

  • Lewis Structure of BF3: BF3 has a trigonal planar structure with 120° bond angles. It is nonpolar because the dipoles cancel.

  • Most Polar Bond: H–F is the most polar due to the largest electronegativity difference.

  • CO2 vs. H2O Polarity: CO2 is nonpolar (linear, dipoles cancel); H2O is polar (bent, dipoles do not cancel).

Example: Draw the Lewis structure for BF3 and show that all B–F bonds are equivalent.

Molecular Geometry (VSEPR)

Predicting Shapes and Bond Angles

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

  • NH4+ Geometry: Tetrahedral, with bond angles of approximately 109.5°.

  • Electron Geometry of CH2O: Trigonal planar (three regions of electron density).

  • SO3 Geometry: Trigonal planar, 120° bond angles.

  • Bond Angles Comparison: NH3 (107°) vs. CH4 (109.5°); lone pairs on NH3 compress bond angles.

Additional info: Lone pairs decrease bond angles compared to ideal geometries.

Compounds & Nomenclature

Writing Formulas and Naming Compounds

Chemical nomenclature follows systematic rules for naming and writing formulas of compounds.

  • Iron (III) Sulfate: Formula is Fe2(SO4)3.

  • K2Cr2O7: Name is potassium dichromate.

  • Ammonium Hydroxide: Formula is NH4OH.

  • SnCl4: Name is tin(IV) chloride.

Compound

Formula

Name

Iron (III) sulfate

Fe2(SO4)3

Iron (III) sulfate

Potassium dichromate

K2Cr2O7

Potassium dichromate

Ammonium hydroxide

NH4OH

Ammonium hydroxide

Tin(IV) chloride

SnCl4

Tin(IV) chloride

Electron Configurations

Writing and Interpreting Configurations

Electron configurations describe the arrangement of electrons in an atom. They are essential for understanding chemical properties.

  • Orbital Diagram for Phosphorus (Z=15): (with arrows showing electron spins in each orbital).

  • Noble Gas Configuration for Sr:

  • Electron Configuration for Fe2+:

  • Noble Gas Configuration for Iodine:

Additional info: Noble gas configurations use the previous noble gas to abbreviate inner electrons.

Lewis Structures & Polarity

Drawing and Interpreting Lewis Structures

Lewis structures show the arrangement of valence electrons in molecules, helping predict geometry and polarity.

  • ClO3− Lewis Structure: Central Cl atom bonded to three O atoms, with one negative charge distributed as a lone pair or formal charge on an O.

  • Geometry: Trigonal pyramidal due to one lone pair on Cl.

Example: Draw ClO3− with three Cl–O bonds and one lone pair on Cl.

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