Atomic Structure, Isotopes, and Ions

Atomic Structure

• Atoms: Fundamental units of all matter.

• Subatomic Particles & Location

  • Nucleus: Dense center, holds most mass. Contains protons and neutrons.

  • Electron Cloud: Region around nucleus, holds most volume. Contains electrons.

Subatomic Particles: Charges & Role

• Proton (p⁺): Charge +1. Determines element (Atomic Number Z).

• Neutron (n⁰): Charge 0. Varies in isotopes.

• Electron (e⁻): Charge-1 . Controls chemical reactions and bonding.

Atomic Number (Z)

• Definition: Number of protons.

• Key Points

  • Uniquely identifies each element.

  • Equals electrons in a neutral atom.

Mass Number & Isotopes

• Mass Number (A): Sum of protons and neutrons (not on periodic table).

• Isotopes: Same element (same Z), different neutrons (different A).

• Isotope Notation: {}^{A}_ {Z}X (e.g., {}^{14}_ {6}C has 6 protons, 8 neutrons).

Atomic Mass Unit (u)

• Standard unit for atomic masses, approximate mass of proton or neutron.

Average Atomic Mass

• Weighted average mass of an element's naturally occurring isotopes (on periodic table).

• Formula: \overline{M} = (\text{fraction of isotope }1\times \text{mass of isotope }1) + (\text{fraction of isotope }2\times \text{mass of isotope }2) + \dots

Elements, Ions, and Charge Balance

• Element: Substance of only one type of atom.

• Ion Formation: Atoms lose/gain electrons to form ions.

  • Cation: Positive ion (loses electrons).

  • Anion: Negative ion (gains electrons).

• Relevance: Ionic charge affects conductivity and chemical behavior.