Chemistry Study Notes

Polar vs Nonpolar Bonds
- Hydrogen Fluoride (HF):
- Electronegativity: 1.9
- Polarity: Highly polar, close to ionic.
- Carbon Iodine (CI):
- Electronegativity: Carbon = 2.5, Iodine = 2.5
- Polarity: Nonpolar covalent bond; electronegativity difference (ΔEN) = 0.
- Alternative term: Pure covalent bond.
Importance of Electronegativity:
- Used in determining bond polarity: nonpolar covalent (ΔEN = 0) vs polar covalent (0 < ΔEN < 1.9) vs ionic (ΔEN >= 2.0).
Organic Chemistry Overview:
- Composed mostly of H, C, N, and O (90% of compounds in organic chemistry).
- Organic compounds often include structures like C-H bonds and chains.
Bond Types in Organic Compounds:
- C-C Bond: ΔEN = 0 (nonpolar).
- C-H Bond: ΔEN = 0.4 (considered nonpolar).
- C-N Bond: ΔEN = 0.5 (polar).
- H-F Bond: ΔEN = 1.9 (polar).
- Polar vs Nonpolar Bonds: Remember polarity cutoffs:
- Nonpolar: C-H
- Polar: C-N, H-F.

Structure of the Periodic Table:
- Groups: Vertical columns with similar chemical properties.
- Periods: Horizontal rows that indicate electron shell filling.
- Metals predominantly on left; nonmetals on right (H is an exception).
Valence Electrons:
- Elements in the same group have similar valence electron counts explaining similarities in their chemical properties.
- Common counts for groups:
- Group 1: 1
- Group 2: 2
- Groups 13-18: Increase from 3 to 8.

Electron Configurations:
- Example: shorthand for Vanadium (V)
- Neon (Ne) as previous noble gas
- Configuration: [Ne] 3s^2 3p^6 3d^3.
Valence Electrons:
- Valence determination from electron configuration, e.g., Vanadium has 2 outermost electron in the fourth shell.
- Exceptions occur in transition metals where D and S orbitals can shift.
Isoelectronic Species:
- Definition: Two atoms or ions having the same electron configuration.
- Example:
  - F^-
  - O^{2-}
  - Na^{+}
  - Mg^{2+}
- Isoelectronic species have different numbers of protons but the same number of electrons and thus different chemical properties despite identical electron configurations.

Effective Nuclear Charge (Z_eff):
- Significance: The net positive charge experienced by an electron in a multi-electron atom.
- Influential in determining atomic and ionic sizes; generally, greater Z_eff leads to smaller atomic radii due to stronger attraction between the nucleus and electrons.
Size Trends:
- General trend: Atomic size increases down a group, decreases across a period due to increasing Z_eff.
- For isoelectronic species, compare sizes based on Z_eff.

Valence Bond Theory:
- Concept of Hybridization: Combine S and P orbitals to create hybrid orbitals (e.g., sp, sp², sp³).
- Example: sp³ Hybridization = one s orbital and three p orbitals blended together producing four equivalent orbitals.
Molecular Geometry and Shape:
- Understand shapes based on electron pairs and molecular configurations (e.g., Tetrahedral, Trigonal Pyramid).
- Use VSEPR theory to predict molecular geometry from electron domain arrangements.

Ionic Compounds:
- Formation involves transfer of electrons (e.g., from metals to nonmetals).
- Naming involves cation followed by anion with appropriate charges indicated (e.g., MgCl₂ = Magnesium Chloride).
Covalent Compounds:
- Use of prefixes (mono-, di-, tri-, etc.) to denote the number of atoms in the compound name
- Example: CO₂ is carbon dioxide.

Understanding Moles:
- Definition: A mole is defined as 6.022 imes 10^{23} representative particles (Avogadro's number).
- Conversion between moles, molecules, and atoms with ratios based on chemical formulas.