Unit One Atomic Structure & Theory (part 1)

Atomic Structure Components

• Proton (p^+): Positively charged particle located in the nucleus; mass approximately 1.673 x 10^-24 grams.
• Neutron (n^0): Neutral particle located in the nucleus; mass approximately 1.673 x 10^-24 grams.
• Electron (e^-): Negatively charged particle found in the electron cloud; mass approximately 9.11 x 10^-28 grams.

Atomic Properties

• Mass of an atom is attributed to protons and neutrons.
• Volume of an atom is determined by the electron cloud.

Atomic Number and Charge

• Atomic Number: Represents the number of protons in an atom; defines the element and dictates the arrangement of elements on the periodic table.
• Atoms are neutral when protons equal electrons. Positive charge occurs when protons exceed electrons, and negative charge occurs when electrons exceed protons.

Example Calculations

• Sodium (Na) has 11 protons and 11 electrons when neutral.
• Potassium ion (K^+) has 20 protons and 19 electrons (one less due to a positive charge).
• Chlorine ion (Cl^-) has 17 protons and 18 electrons (one more due to a negative charge).
• Oxygen ion with a charge of -2 (O^2-) has 8 protons and 10 electrons.

Isotopes and Composition

• Isotopes are variants of the same element differing in neutron count. All isotopes have the same atomic number.
  • Examples:
    • Hydrogen-1: 1 proton, 0 neutrons
    • Hydrogen-2: 1 proton, 1 neutron
    • Hydrogen-3: 1 proton, 2 neutrons
• Knowledge of mass number and atomic number enables determination of isotopic composition.
• Number of neutrons calculated as: Mass number - Atomic number.

Elemental Examples

• Magnesium (mass number 24): Contains 12 protons, 12 neutrons, and 12 electrons.
• Zinc ion (Zn^4+) has 30 protons, 35 neutrons, and 26 electrons (4 electrons less).

Atomic Representation

• Isotopic Notation: Indicates mass and atomic number, e.g., Oxygen-16 (16 O, 8).
• Name and Number Method: E.g., Carbon-18 indicates mass number.

Average Atomic Mass and Abundance

• Atomic mass is the weighted average of isotopes; it is not the same as mass number.
• To determine abundance, identify the isotope nearest to the element's average atomic mass.

Calculation of Average Atomic Mass

• For isotopes with varying percentages:
  • Calculate average atomic mass using the formula:
    • (Mass1 * Abundance1) + (Mass2 * Abundance2) + ...

Additional Examples

• Element with 38 protons and 45 neutrons identified as Strontium (Sr).
• Most abundant isotopes typically have masses closest to the average atomic mass on the periodic table.

Additional Concepts in Atomic Structure

• Ions: Atoms with unequal numbers of protons and electrons, categorized by charge (positive or negative).
• Nuclides: Unique nuclear species characterized by proton and neutron counts.
• Nucleons: General term for protons and neutrons within an atomic nucleus.