Chapter 3.5: The Mole and Mole Conversions

What is a Mole?

The mole is a fundamental unit in chemistry used to count particles such as atoms, molecules, or ions. It is analogous to terms like "dozen" or "gross" but represents a much larger quantity. One mole contains exactly 6.022 × 1023 entities, a value known as Avogadro's number.

• Definition: 1 mole (mol) = 6.022 × 1023 particles (atoms, molecules, etc.)

• Examples: 1 mol of marbles = 6.022 × 1023 marbles; 1 mol of sand grains = 6.022 × 1023 grains.

Mole Conversions: Atoms to Moles and Vice Versa

Conversions between moles and number of atoms use Avogadro's number as a conversion factor. This is similar to converting between dozens and individual items.

• Conversion factor: 1 mol atoms = 6.022 × 1023 atoms

• Example Calculation:

  • Number of copper atoms in 2.45 mol of copper:

  • Moles of silver in 2.80 × 1022 atoms:

Molecular Weight and Moles of Compounds

The molecular weight (MW) of a compound is the sum of the atomic masses of all atoms in its formula. It allows conversion between grams and moles.

• Example: Glucose (C6H12O6)

  • MW = 6(12.01 g/mol) + 12(1.01 g/mol) + 6(16.00 g/mol) = 180.16 g/mol

  • Moles in 100 g glucose:

Chapter 4: Introduction to Organic Compounds

Overview of Chapter 4

• 4.1 – Structures of Organic Compounds

• 4.2 – Alkanes

• 4.3 – Functional Groups

• 4.4 – Nomenclature (Naming of Organic Compounds)

• 4.5 – Isomerism

4.1 Structures of Organic Compounds

What are Organic Compounds?

Organic compounds are covalent compounds that contain carbon. They may also include hydrogen, oxygen, nitrogen, and other elements. The unique bonding properties of carbon allow for a vast diversity of molecular structures.

• Key elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), etc.

• Importance: Organic compounds are the basis of all life and include carbohydrates, proteins, lipids, and nucleic acids.

Valence Electrons and Bonding

Valence electrons are the outermost electrons of an atom and are responsible for forming chemical bonds. The number of valence electrons determines an element's bonding behavior.

• Group number: For main group elements, the group number indicates the number of valence electrons.

• Example: Carbon (Group 4A) has 4 valence electrons.

Lewis Dot Structures

Lewis structures are diagrams that show the arrangement of atoms and valence electrons in a molecule. They help visualize bonding and lone pairs.

• Carbon bonding: Carbon forms four single bonds (e.g., CH4), double bonds (e.g., CO2), or triple bonds (e.g., HCN).

• Hydrogen: Always forms one single bond.

Strategy for Drawing Lewis Dot Structures

Drawing Lewis structures involves a systematic approach to ensure all atoms achieve stable electron configurations (octet rule).

1. Count total valence electrons.

2. Determine the central atom (usually least electronegative; H is never central).

3. Connect surrounding atoms to the central atom with single bonds.

4. Add remaining electrons to outer atoms to satisfy the octet rule (H only needs 2 electrons).

5. Place any remaining electrons on the central atom.

6. Check for correct electron count and octet fulfillment.

7. Form multiple bonds if necessary.

Practice: Lewis Structures for Simple Molecules

• HCl: H–Cl (single bond)

• C2H4: H2C=CH2 (double bond between carbons)

• H2O: H–O–H (two single bonds, two lone pairs on O)

Condensed and Skeletal Structures

Organic molecules can be represented in several ways, each with varying levels of detail:

• Molecular formula: Shows the number of each type of atom (e.g., C3H8).

• Condensed structure: Groups atoms to show connectivity (e.g., CH3CH2CH3).

• Lewis structure: Shows all atoms and bonds explicitly.

• Skeletal structure: Uses lines to represent carbon-carbon bonds; hydrogens on carbons are implied.

4.2 Alkanes

Properties and Structure of Alkanes

Alkanes are the simplest family of organic molecules, consisting only of carbon and hydrogen atoms connected by single bonds. They are called saturated hydrocarbons because each carbon is bonded to the maximum number of hydrogens.

• Straight-chain alkanes: Unbranched chains of carbon atoms.

• General formula: CnH2n+2

Naming Alkanes

Alkanes are named based on the number of carbon atoms in the longest continuous chain. The prefixes meth-, eth-, prop-, but-, etc., indicate the number of carbons.

Cycloalkanes

Cycloalkanes are alkanes in which the carbon atoms are arranged in a ring. Their names are formed by adding the prefix "cyclo-" to the alkane name. Rings of five and six carbons are especially common in nature.

Polarity of Alkanes

Alkanes are nonpolar molecules because the electronegativities of carbon and hydrogen are very similar, resulting in equal sharing of electrons in C–H bonds. This nonpolarity affects their solubility and physical properties.

Summary Table: Types of Organic Structure Representations

Additional info: This guide covers foundational concepts in organic chemistry, including the mole, molecular representations, and the structure and nomenclature of alkanes and cycloalkanes. These topics are essential for understanding more advanced organic chemistry concepts such as functional groups, isomerism, and reactivity.