Comprehensive Chemistry Notes: Isomers, The Periodic Table, Ionic/Molecular Compounds, and Formula Mass

Isomers

• Isomers are compounds with the same molecular formula but different atomic connectivity or spatial arrangements.

• They include structural and spatial (stereochemical) isomers.

• Example: S-(+)-carvone and R:(−)-carvone are enantiomers (non-superimposable mirror images) with different smells.

2.5 The Periodic Table

• Periodic Law: Properties of elements are periodic functions of their atomic numbers.

• Organization: Elements are arranged by increasing atomic number in seven periods (rows) and 18 groups (columns).

• Classification:

  • Metals: Shiny, malleable, ductile, good conductors.

  • Nonmetals: Dull, poor conductors.

  • Metalloids: Intermediate properties.

• Main Groups: Columns 1, 2, 13–18. Transition Metals: Columns 3–12. Inner Transition Metals: Lanthanides and Actinides.

• Group Names: Group 1 (alkali metals), Group 2 (alkaline earth metals), Group 17 (halogens), Group 18 (noble gases).

• Elements in the same group share similar chemical behaviors due to comparable outer-shell electron configurations.

2.6 Ionic and Molecular Compounds

• Bonds:

  • Ionic: Electrostatic attraction between oppositely charged ions (electron transfer, typically metal + nonmetal).

  • Covalent (Molecular): Sharing electron pairs between atoms (typically nonmetals).

• Ion Formation (Main-Group):

  • Metals lose electrons to form cations (charge often equals group number).

  • Nonmetals gain electrons to form anions (charge completes noble-gas configuration).

• Types of Ions:

  • Monatomic: Single atom ions (e.g., $Na^+$, $Cl^−$).

  • Polyatomic: Groups of bonded atoms with an overall charge (e.g., $OH^−$, $SO_4^{2−}$).

• Ionic Compound Formulas: Must be electrically neutral; written as the simplest ratio of ions (e.g., $NaCl$, $CaCl_2$).

3.1 Formula Mass and the Mole Concept

• Formula Mass: The sum of the average atomic masses of all atoms in a compound's formula unit.

  • For covalent substances, it's called molecular mass (e.g., $M<em>{CHCl</em>3} = M<em>C + M</em>H + 3 M_{Cl}$.

  • For ionic compounds, it's the sum for the empirical formula (e.g., $M<em>{NaCl} = M</em>{Na} + M_{Cl}$).

• The Mole: A counting unit linking macroscopic mass to a number of entities.

• Avogadro’s Number ($N_A$): $6.022 imes 10^{23} ext{ entities/mol}$.

• Molar Mass: The mass in grams of 1 mole of a substance; numerically equivalent to formula mass in amu.

• Relationships:

  • $n = rac{m}{M}$ (moles = mass / molar mass).

  • $N = n imes N_A$ (number of entities = moles x Avogadro's number).