Week4

Week 4 Overview

• Topics Covered:

  • 2.4 Chemical Formulas

  • 2.5 The Periodic Table

  • 2.6 Molecular and Ionic Compounds

  • 2.7 Chemical Nomenclature

Section 2.4: Chemical Formulas

Learning Objectives

• Symbolize molecular composition using:

  • Molecular formulas

  • Empirical formulas

• Represent bonding arrangements with structural formulas.

Chemical Formulas

• Molecular Formula:

  • Represents type and number of atoms.

  • Uses chemical symbols and subscripts (e.g., H₂O).

  • Structural Formula:

    • Shows how atoms connect in a molecule.

Molecular vs. Structural Formulas

• Representations of Methane:

  • Molecular Formula: CH₄

  • Structural Formula: Shows connections between carbon and hydrogen atoms.

  • Ball-and-stick Model & Space-Filling Model: Show 3D arrangement.

Diatomic and Polyatomic Molecules

• Diatomic Molecules:

  • Examples include H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂.

• S₈ (Elemental Sulfur): Contains 8 sulfur atoms arranged to form a molecule.

Empirical vs. Molecular Formulas

• Empirical Formula: Simplest ratio of atoms (e.g., CH for C₆H₆).

• Molecular Formula: Actual number of atoms in the molecule.

  • Examples:

    • Benzene:

      • Molecular: C₆H₆

      • Empirical: CH

    • Acetic Acid:

      • Molecular: C₂H₄O₂

      • Empirical: CH₂O

Isomers

• Isomers: Same molecular formula, different structures (e.g., acetic acid and methyl formate).

Spatial Isomers

• Carvones: Exist as spatial isomers differing in atom orientations.

Section 2.5: The Periodic Table

Learning Objectives

• State the periodic law.

• Predict general properties based on periodic table location.

• Identify metals, nonmetals, and metalloids.

Discovering the Periodic Table

• Developed independently by Dimitri Mendeleev and Lothar Meyer in the 1860s.

• Recognized periodic relationships among element properties (e.g., Li, Na, K).

The First Periodic Table

• Organized elements by increasing atomic mass, predicting properties of unknown elements (gallium and germanium).

Modern Periodic Table

• Organized by atomic numbers rather than mass.

• Periodic Law: Element properties show periodic functions of atomic numbers.

• Table Structure:

  • Periods (horizontal) and groups (vertical, numbered 1–18).

Classifications of Elements

Element Properties

• Metals: Shiny, malleable, good conductors.

• Nonmetals: Dull, poor conductors.

• Metalloids: Exhibit properties of both metals and nonmetals.

Special Groups of Elements

• Groups 1-18:

  • Alkali metals, alkaline earth metals, halogens, noble gases, etc.

Section 2.6: Molecular and Ionic Compounds

Learning Objectives

• Define ionic and molecular compounds.

• Predict compound formation based on periodic table position.

Bonding Basics

• Chemical Reactions: Electrons are transferred or shared; nuclei remain unchanged.

• Ions Formation: Gaining or losing electrons plays a crucial role in chemical reactions.

Predicting Ion Charges

• Main-Group Elements:

  • Metals (Groups 1 & 2) lose electrons to match noble gas configuration.

  • Nonmetals (Groups 16 & 17) gain electrons.

Examples of Charge Prediction

• Example of Calcium (Ca):

  • Loses 2 electrons → Ca²+

• Example of Bromine (Br):

  • Gains 1 electron → Br−

Polyatomic Ions

• Definition: Charged molecules consisting of multiple atoms.

• Oxyanions: Polyatomic ions containing oxygen (e.g., sulfate, nitrate).

Naming and Formulas of Ionic Compounds

• Name the cation first, followed by the anion.

• Charges for metals specified using Roman numerals.

Properties and Characteristics of Ionic Compounds

• Generally high melting/boiling points.

• Non-conductive as solids, conductive in molten form.

Section 2.7: Chemical Nomenclature

Learning Objectives

• Derive names for common inorganic compounds.

Basic Nomenclature Rules

• Naming Ionic Compounds:

  • Monoatomic cation names are taken from the element name; anions change to –ide.

• Transition Metals: Use Roman numerals to indicate the charge (e.g., FeCl₂ = iron(II) chloride).

Naming Binary Covalent Compounds

• Names based on the number of atoms using Greek prefixes.

• Drop 'mono-' for the first element if the quantity is one.