Foundations of Chemical Change: Equations and Stoichiometry

TL;DR

This topic covers how to write and interpret chemical equations, focusing on organic reactions like elimination, addition, and substitution, while ensuring atoms and mass are conserved. You'll also learn about different organic compound structures, functional groups, and how to define key terms like molecular formula and homologous series. We'll also touch on catalysts and acid-base reactions.

1. The Mental Model

Think of chemistry as building with LEGOs. Chemical equations are your instruction manuals, showing exactly which pieces (atoms) combine, rearrange, or break apart to make new things, always making sure you don't lose any pieces along the way.

2. The Core Material

Organic Molecular Structures and Definitions

Let's start with the building blocks of organic chemistry.

• Molecular formula: This tells you exactly which elements and how many of each atom are in a molecule. E.g., C$_2$H$_6$ for ethane.
• Homologous series: These are families of organic compounds that share a general formula or where one member differs from the next by a CH$_2$ group. They have similar chemical properties.
• Saturated compounds: These have no multiple bonds between carbon atoms in their hydrocarbon chains. Think of them as "full" with hydrogens—only single C-C bonds.
• Unsaturated compounds: These have one or more multiple bonds (double or triple) between carbon atoms in their hydrocarbon chains. They are "not full" and can add more atoms.
• Functional group: This is the specific atom or group of atoms that largely determines a compound's physical and chemical properties. It's the "active" part of the molecule.
• Structural isomer: Organic molecules that have the same molecular formula but different structural formulae. They are made of the same atoms but are put together differently.

Here's a breakdown of common functional groups and homologous series:

Advanced Stoichiometric Calculations

TL;DR

You'll learn to calculate amounts of chemicals in reactions, figure out what's left over, and determine exact formulas. We'll also cover reaction speeds and how concentration affects things at equilibrium. This means combining what you know about moles, balanced equations, and specific reaction conditions to solve problems.

1. The Mental Model

Think of stoichiometry as a recipe for chemistry: it tells you exactly how much of each ingredient you need and how much product you'll get. Advanced calculations just mean those recipes might have extra steps, like figuring out what ingredient runs out first or how fast the recipe is made.

2. The Core Material

Empirical and Molecular Formulas

The empirical formula is the simplest whole-number ratio of atoms in a compound. The molecular formula is the actual number of atoms in a molecule.
1. Find the empirical formula:
* Convert given masses (or percentages) of elements to moles.
* Divide all mole values by the smallest mole value to get a simple ratio.
* If you don't get whole numbers, multiply by a small integer to make them whole.
2. Find the molecular formula:
* Calculate the empirical formula mass.
* Divide the given molecular mass by the empirical formula mass to get a whole number (n).
* Multiply each subscript in the empirical formula by 'n'.

Stoichiometric Calculations with Balanced Equations

These calculations use the mole ratios from a balanced chemical equation to convert between amounts of reactants and products.
1. Balance the chemical equation.
2. Convert the given quantity (mass, volume, etc.) of a substance to moles.
3. Use the mole ratio from the balanced equation to find the moles of the desired substance.
4. Convert the moles of the desired substance to the required units (mass, volume, etc.).

Stoichiometric Calculations with Limiting Reagents

In many reactions, one reactant will run out before others. This is the limiting reagent (or reactant), and it determines the maximum amount of product that can be formed.
1. Balance the equation.
2. Calculate the moles of all reactants.
3. Determine the limiting reagent: For each reactant, calculate how much product could be formed if that reactant were completely consumed. The reactant that yields the least amount of product is the limiting reagent.
4. **Use the moles of the limiting rea

Intermolecular and Interatomic Forces

TL;DR

Forces between molecules (intermolecular) are weaker than forces within molecules (interatomic/chemical bonds). These forces affect physical properties like boiling point and melting point, with stronger forces leading to higher values. Molecular size also influences intermolecular force strength, especially for non-polar molecules.

1. The Mental Model

Imagine molecules as tiny Lego bricks. Interatomic forces are the strong studs that hold a single Lego brick together. Intermolecular forces are like the weaker static cling or magnetic pull that makes several bricks stick together loosely.

2. The Core Material

Intermolecular Forces (Van der Waal's forces)

These are forces between molecules. Your notes highlight three main types:

• Dipole-dipole forces: These occur between two molecules that are polar. Polar molecules have a slight positive end and a slight negative end due to uneven sharing of electrons. The positive end of one molecule is attracted to the negative end of another.
• Induced dipole forces or London forces: These are present between all molecules, but they are the primary force between non-polar molecules. They arise from temporary, fluctuating dipoles caused by the random movement of electrons. The strength of these forces increases with molecular size.
• Hydrogen bonding: This is a special, strong type of dipole-dipole force. It happens when hydrogen is covalently bonded to a highly electronegative atom like nitrogen (N), oxygen (O), or fluorine (F). The hydrogen atom becomes very positive, and is strongly attracted to a lone pair of electrons on an N, O, or F atom of an adjacent molecule.

Interatomic Forces (Chemical Bonds) vs. Intermolecular Forces

It's crucial to understand the difference between forces within a molecule and forces between molecules.

• Interatomic Forces / Chemical Bonds (Intramolecular forces): These are the strong forces that hold atoms together within a single molecule. Examples include covalent bonds (like C-H in methane) or ionic bonds. These are much stronger than intermolecular forces.
• Intermolecular Forces: These are the weaker forces that exist between separate molecules. Breaking these forces (e.g., when boiling water) doesn't break the individual molecules themselves.

Let's look at methane (CH₄) to visualize this:

```mermaid
graph TD
subgraph "Single Methane Molecule"
C1[Carbon] ---