Fundamental Chemistry Concepts for Anatomy & Physiology

Chemical Bonding and Molecular Structure

Covalent and Ionic Compounds

Chemical compounds can be classified based on the type of bond that holds their atoms together. Understanding these differences is essential for grasping how molecules interact in biological systems.

• Covalent Compounds: Atoms share electrons. Typically formed between nonmetals (e.g., HCl).

• Ionic Compounds: Atoms transfer electrons, resulting in oppositely charged ions that attract each other. Usually formed between metals and nonmetals (e.g., NaBr).

• Example: HCl is covalent, while NaBr is ionic.

Polarity of Molecules

Molecular polarity affects how molecules interact, dissolve, and react in biological systems.

• Polar Molecules: Have an uneven distribution of electron density, resulting in partial charges (e.g., CHBr3).

• Nonpolar Molecules: Have an even distribution of electron density.

• Example: CHBr3 is polar due to the presence of different atoms with varying electronegativities.

Electronegativity

Electronegativity is a measure of an atom's ability to attract electrons in a chemical bond. It determines bond polarity and molecular interactions.

• Order of Electronegativity: F > Cl > Br

• Example: Fluorine is the most electronegative element, followed by chlorine and then bromine.

Chemical Formulas and Lewis Structures

Lewis Structures

Lewis structures represent the arrangement of electrons in a molecule, showing how atoms are bonded and the presence of lone pairs.

• Key Features: Dots represent valence electrons; lines represent covalent bonds.

• Application: Used to predict molecular shape and reactivity.

Covalent Bonds and Valence Electrons

The number of covalent bonds an atom forms is often determined by the number of valence electrons it has.

• Atoms with Five Valence Electrons: Typically form three covalent bonds (e.g., nitrogen in NH3).

Redox Reactions

Oxidation and Reduction

Redox (reduction-oxidation) reactions involve the transfer of electrons between substances. These reactions are fundamental in metabolism and cellular respiration.

• Oxidation: Loss of electrons (metals tend to undergo oxidation).

• Reduction: Gain of electrons.

• Oxidizing Agent: The substance that gains electrons and causes another to be oxidized.

Half-Reactions

Redox reactions can be split into two half-reactions: one for oxidation and one for reduction.

• Example: Ni2+(aq) + Mg(s) → Ni(s) + Mg2+(aq)

• Oxidation: Mg(s) → Mg2+(aq) + 2e-

• Reduction: Ni2+(aq) + 2e- → Ni(s)

Chemical Equations and Stoichiometry

Balancing Chemical Equations

Balanced chemical equations ensure the conservation of mass and atoms in a reaction.

• Example: 2 SO2 + O2 + 2 H2O → 2 H2SO4

Stoichiometric Calculations

Stoichiometry involves using balanced equations to calculate the amounts of reactants and products.

• Mole-to-Mole Ratios: Derived from coefficients in balanced equations.

• Example: In CaCl2 + 2 NaOH → Ca(OH)2 + 2 NaCl, the ratio is 1 mol Ca(OH)2 / 2 mol NaOH.

Mole Concept and Avogadro's Number

Moles and Avogadro's Number

The mole is a fundamental unit in chemistry, representing 6.022 × 1023 entities (Avogadro's number).

• Calculating Atoms: Number of atoms = moles × Avogadro's number.

• Example: 3.85 mol of carbon contains 2.32 × 1024 atoms.

Mole Calculations in Compounds

To find the number of atoms in a compound, multiply the number of moles by the number of atoms per molecule and Avogadro's number.

• Example: 77.28 g of ethane (C2H6) contains 1.548 × 1025 carbon atoms.

Mass-Mole Conversions

Converting Between Mass and Moles

Use the molar mass (g/mol) to convert between mass and moles.

• Formula: $\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$

• Example: 211 g of CO2 contains 4.79 mol of CO2.

Tables

Electronegativity Order Table

The following table summarizes the order of electronegativity for selected halogens:

Element	Electronegativity (Pauling Scale)
F (Fluorine)	3.98
Cl (Chlorine)	3.16
Br (Bromine)	2.96

Redox Half-Reactions Table

Example of half-reactions for Ni2+ and Mg:

Species	Half-Reaction	Type
Mg(s)	Mg(s) → Mg2+(aq) + 2e-	Oxidation
Ni2+(aq)	Ni2+(aq) + 2e- → Ni(s)	Reduction

Additional info:

• These chemistry concepts are foundational for understanding physiological processes, such as cellular respiration, enzyme function, and molecular transport in Anatomy & Physiology.