Atomic Theory and Structure of Atoms

Atomic Theory

• Atoms are the smallest unit of an element, maintaining its identity.
• The term "atom" comes from a Greek word meaning "indivisible."
• Atoms are composed of subatomic particles.

Modern Atomic Theory

• All matter is composed of atoms.
• Atoms of the same element are identical; atoms of different elements are different.
• Atoms combine in whole-number ratios to form compounds.

The Atom

• Protons: Located in the nucleus; have a positive charge (1+) and a mass of approximately 1.6 × 10^-27 kg.
• Neutrons: Located in the nucleus; have no charge and a mass of approximately 1.6 × 10^-27 kg.
• Electrons: Orbit the nucleus; have a negative charge (1-) and a mass of approximately 9.1 × 10^-31 kg.

Atomic Number

• The number of protons in an atom's nucleus defines the atomic number.
• All atoms of the same element have the same atomic number.
• However, atoms of the same element can have different numbers of neutrons.

Isotopes

• Atoms of the same element with different numbers of neutrons are called isotopes.
• The mass number is the sum of protons and neutrons in an atom's nucleus.

Atomic Symbols

• Atomic symbols use the element's symbol followed by the mass number (protons + neutrons).
• Example: Carbon-12 (¹²C) represents an isotope of carbon with 6 protons and 6 neutrons.

Periodic Table of Elements

• Organized by increasing atomic number.
• Elements' properties are related to their position on the table.
• Elements are categorized as metals, metalloids, and nonmetals.

Molecules and Chemical Nomenclature

• Molecules: Two or more atoms bonded strongly, behaving as a single particle.
• Molecular Formula: A written representation of the number and type of atoms in a molecule. Example: H₂ (two hydrogen atoms).
• Chemical Nomenclature: Rules for naming compounds.

Rules of Chemical Nomenclature

• Identify the elements in the compound.
• Start with the first element's name, using prefixes (e.g., mono-, di-, tri-) for additional atoms if needed.
• Name the second element, incorporating prefixes (if needed) and changing its ending to "-ide."
• Combine the names. Example: carbon dioxide (CO₂)
• Specific rules apply when prefixes end in "a" or "o" and the second element begins with a vowel. e.g. monoxide, pentoxide.