Chemistry

Chapter 3: Periodicity and Off-Tech

• Transition from Chapter 2 to periodicity in the context of the periodic table.

• Emphasis on periodic trends and behaviors of elements based on their positions in the periodic table.

  • Most elements adhere to periodic trends, while some may deviate.

Five-Step Process for Structure Cleanup

1. Counting Electrons

   • Determine the total number of electrons in the structure.

2. Formal Charge Calculation

   • Create and visualize possible resonance structures and their stability.

   • Calculate and compare formal charges to identify the most stable structure.

   • Utilize a formal charge formula for calculations.

Key Concepts

• Formal Charge:

  • A value calculated for atoms within a molecule to assess their stability.

  • Structures with formal charges close to zero generally preferred for stability.

  • Nitrogen tends to have a -1 formal charge when bonded appropriately.

• Resonance Structures:

  • Atoms can exist in different arrangements leading to multiple valid Lewis structures.

  • More stable structures are favored, exhibiting resonant characteristics.

Naming Covalent Compounds

• Covalent compounds (p-block elements, nonmetal-to-nonmetal) differ from ionic compounds in naming conventions.

  • Use prefixes to indicate the number of each atom in the formula (e.g., Carbon Monoxide, Carbon Dioxide).

  • In contrast to ionic compounds where no prefixes are needed (e.g., Sodium Chloride).

Types of Acids

• Binary Acids:

  • Named with the prefix 'hydro' and the nonmetal plus 'ic' (e.g., HCl as Hydrochloric Acid).

• Oxyacids:

  • Named based on polyatomic ions; suffix 'ate' becomes 'ic' and 'ite' becomes 'ous' (e.g., HNO3 as Nitric Acid from Nitrate).

Valence Shell Electron Repulsion (VSEPR) Theory

• Focus on the spatial arrangement of electron pairs around a central atom.

  • Electron pairs repel each other, leading to distinct molecular shapes and bond angles.

• Common Geometries:

  • Linear: Two atoms (180° angle).

  • Trigonal Planar: Three bonding pairs (120° angle).

  • Tetrahedral: Four bonding pairs (109.5° angle).

  • Shapes alter with lone pairs affecting angles.

Example of Molecular Shapes

• Bent Shapes arise from lone pair presence amidst multiple bonds.

• Tetrahedral Geometry is established with four electron clouds (single/double bonds and lone pairs).

Practical Applications and Stability

• Resonance contributes to the stability and identity of chemical species.

• Relating structures to chemical behavior in natural systems (example: oxygen in respiration).

• Understanding these concepts is vital for recognizing stability markers in compounds, predicting reactiveness, and naming accurately in chemistry.