Chapter 5: Atoms, Molecules, and Subatomic Particles

Atoms

Definition: Smallest particle of an element with properties of that element.
Element: Cannot be broken down chemically.
Atomic Theory of Matter (Dalton's Atomic Theory):
- All matter is composed of atoms.
- 118 types of atoms exist.
- Atoms of the same element are similar.
- Arrangement and combination of atoms determine substance identity (e.g., water is H₂O).
- Atoms can rearrange or unite to form new substances but cannot be destroyed.
- Diameter of atoms: 0.1 to 0.5 nanometers (10 million hydrogen atoms across 1 mm).

Diatomic: Two atoms (e.g., H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂).
- Mnemonic: "Horses Need Oats For Clear Brown Eyes"
Triatomic: Three atoms (e.g., O₃ - ozone).
Polyatomic: Many atoms (e.g., P₄, S₈).
Homoatomic: Atoms of the same kind (e.g., H₂, O₃).
Heteroatomic: Different kinds of atoms (e.g., H₂O).

Definition: Composed of heteroatomic molecules (different atoms).
Example: Sucrose (C₁₂H₂₂O₁₁) with 12 carbon, 22 hydrogen, and 11 oxygen atoms.
Characteristics:
- Made of only non-metals.
- Molecule vs. atom: Molecules have different properties.

Example: Sodium chloride (NaCl)
Characteristics:
- Combination of a metal (sodium) and a non-metal (chlorine).
- Consists of a regular repeated pattern of formula units (e.g., Na⁺Cl⁻).

Element: Made of one kind of atom (e.g., silver, copper, iron).
- Examples of homoatomic: Diatomic gases (O₂, F₂, Cl₂).
Compound: Made of two or more types of atoms.
- Examples of heteroatomic: Water (H₂O), hydrogen peroxide.

Structure: Symbols with subscripts indicating atom numbers.
Example:
- H₂O: Two hydrogen atoms, one oxygen atom.
- Glucose: C₆H₁₂O₆ (six carbon, twelve hydrogen, six oxygen).