Atomic Structure and Electron Configuration

Electron Configuration Diagrams

Electron configuration diagrams visually represent the arrangement of electrons in an atom's orbitals, following the Aufbau principle, Pauli exclusion principle, and Hund's rule. The diagram provided asks for the electron configuration of neutral Sulfur (S).

• Aufbau Principle: Electrons fill orbitals starting with the lowest energy level first.

• Pauli Exclusion Principle: Each orbital can hold a maximum of two electrons with opposite spins.

• Hund's Rule: Electrons occupy degenerate orbitals singly before pairing.

Example: Electron Configuration for Sulfur (S, atomic number 16):

• 1s2 2s2 2p6 3s2 3p4

• Orbital diagram: Fill boxes for each subshell according to the number of electrons.

Additional info: Sulfur's electron configuration can be shown as:

Noble Gas Notation

Noble gas notation is a shorthand for electron configuration, using the previous noble gas to represent filled inner shells.

• Se (Selenium, atomic number 34): [Ar] 4s2 3d10 4p4

• Na (Sodium, atomic number 11): [Ne] 3s1

• Pt (Platinum, atomic number 78): [Xe] 4f14 5d9 6s1

Example: For Sodium:

Lewis Structures, Molecular Geometry, and Polarity

Drawing Lewis Structures

Lewis structures depict the arrangement of valence electrons around atoms in a molecule. They help predict molecular shape, bond angles, and polarity.

• Steps:

  1. Count total valence electrons.

  2. Arrange atoms (central atom usually least electronegative).

  3. Connect atoms with single bonds.

  4. Distribute remaining electrons to complete octets.

  5. Form double/triple bonds if necessary.

Molecular Geometry and Bond Angles

The shape of a molecule is determined by the number of bonding pairs and lone pairs around the central atom, as described by VSEPR theory.

Examples: Lewis Structures and Molecular Properties

• PI3 (Phosphorus triiodide):

  • Central atom: P

  • Three I atoms bonded to P, one lone pair on P

  • Shape: Trigonal pyramidal

  • Bond angle: ~107°

  • Polarity: Polar

• SO2 (Sulfur dioxide):

  • Central atom: S

  • Two O atoms bonded to S, one lone pair on S

  • Shape: Bent

  • Bond angle: ~120°

  • Polarity: Polar

• H2O (Water):

  • Central atom: O

  • Two H atoms bonded to O, two lone pairs on O

  • Shape: Bent

  • Bond angle: ~104.5°

  • Polarity: Polar

Additional info: The polarity of a molecule depends on both its shape and the electronegativity difference between atoms.

Chemical Nomenclature

Writing Chemical Formulas from Names

Chemical nomenclature involves converting compound names to formulas and vice versa. The rules differ for ionic and covalent compounds.

• Ionic Compounds: Metal + Nonmetal; use charges to balance formula.

• Covalent Compounds: Nonmetals; use prefixes to indicate number of atoms.

Examples: Name to Formula

Examples: Formula to Name

Additional info: For transition metals, Roman numerals indicate the oxidation state.

Summary Table: Prefixes for Covalent Compounds