Atomic Structure and Bonding: Study Notes

Atomic Structure and Bonding

Introduction

This section covers the fundamental concepts of atomic structure and chemical bonding, which are foundational to understanding organic chemistry. Key topics include the nature of chemical bonds, atomic numbers, mass numbers, and the behavior of elements in chemical reactions.

Atomic Structure

• Atomic Number (Z): The number of protons in the nucleus of an atom. It defines the identity of the element. Example: An atom with 11 protons has an atomic number of 11 (Sodium).

• Mass Number (A): The total number of protons and neutrons in the nucleus. Formula: $A = Z + N$ where $A$ is the mass number, $Z$ is the atomic number (protons), and $N$ is the number of neutrons. Example: An atom with 11 protons and 12 neutrons has a mass number of $11 + 12 = 23$.

Chemical Bonding

• Ionic Bond: A chemical bond formed by the transfer of electrons from one atom to another, resulting in the formation of oppositely charged ions. Example: NaCl (sodium chloride) forms when sodium donates an electron to chlorine.

• Covalent Bond: A chemical bond formed by the sharing of electrons between two atoms. Example: H2O (water) forms when hydrogen and oxygen share electrons.

• Key Difference: In ionic bonds, electrons are transferred; in covalent bonds, electrons are shared.

Noble Gases and Reactivity

• Noble Gases (Group 18): Elements with a full valence shell of electrons, making them chemically inert and unlikely to form bonds with other elements.

• Reason for Inactivity: Their stable electron configuration (octet) means they have little tendency to gain, lose, or share electrons.

Chemical Equations and Balancing

• Balancing Chemical Equations: The process of ensuring the number of atoms for each element is equal on both sides of the equation. Example:

  • Unbalanced: $H_2 + O_2 \rightarrow H_2O$

  • Balanced: $2H_2 + O_2 \rightarrow 2H_2O$

Acids and Bases

• Acid: A substance that increases the concentration of hydrogen ions (H+) in solution. Acids have a pH less than 7.

• Base: A substance that increases the concentration of hydroxide ions (OH-) in solution. Bases have a pH greater than 7.

• pH Scale: A measure of the acidity or basicity of a solution. A pH of 2 indicates a strong acid.

• Example: If a pH strip turns bright red (pH = 2), the substance is an acid.