CHm1032 Unit 2 Isotopes Video

Overview of the Periodic Table of Elements

  • Elements: Simplest substances (e.g., hydrogen, oxygen)

  • Compounds: Formed by combining elements (e.g., water)

Fundamental Concepts in Chemistry

  • Atoms:

    • Building blocks of all substances

    • Consist of three fundamental particles:

    • Protons:

      • Charged: Positively charged

    • Electrons:

      • Charged: Negatively charged

    • Neutrons:

      • Electrically neutral

  • Atomic Neutrality: In neutral atoms, the number of protons equals the number of electrons.

Structure of the Atom

  • Analogy: Atoms compared to a solar system:

    • Nucleus: Like the sun, contains protons and neutrons.

    • Electrons: Orbit around the nucleus like planets.

  • Example with Lithium:

    • Lithium has three protons, indicated by the atomic number 3.

    • Neutral lithium also has three electrons.

    • The atomic number is unique to each element (no other elements have three protons).

Periodic Table Basics

  • Atomic Number:

    • Represents the number of protons in an atom.

    • Determines the identity of the element (e.g., hydrogen has 1, helium has 2).

  • Neutrons:

    • Number of neutrons varies across atoms of the same element (isotopes).

    • Neutrons do not affect chemical properties directly, providing mass and stability to the nucleus by preventing repulsion of protons.

Atomic Properties and Isotopes

  • Isotopes: Atoms of the same element with different numbers of neutrons. Examples include:

    • Carbon:

    • Carbon-12: 6 protons, 6 neutrons → Mass number = 12

    • Carbon-13: 6 protons, 7 neutrons → Mass number = 13

    • Carbon-14: 6 protons, 8 neutrons → Mass number = 14

  • Stability: Neutrons are essential for the stability of the atomic nucleus, as they mitigate the repulsion between the positively charged protons.

  • Mass Number:

    • Sum of protons and neutrons in an isotope.

    • Example:

    • Carbon-12 has a mass number of 12 (6 protons + 6 neutrons).

    • Write isotope symbols as follows:

      • Mass number (top left), Atomic number (bottom left), Element symbol (center).

      • e.g.,  C12 for Carbon-12.

Identifying Isotopes and Their Symbols

  • To write the isotope symbol:

    1. Write the element symbol in the center.

    2. Write the atomic number (number of protons) on the bottom left.

    3. Write the mass number (sum of protons and neutrons) on the top left.

  • Examples:

    • Carbon-12: C₆¹²

    • Carbon-13: C₆¹³

    • Carbon-14: C₆¹⁴

    • Iodine-131 for thyroid cancer treatment uses its mass number for identification.

Practical Exercises: Identifying Isotopes

  1. Hydrogen Isotope: Atomic Number = 1.

    • Mass number = 1 + 0 (0 neutrons) → Symbol: H₁¹.

  2. Nitrogen Isotope: Atomic Number = 7, Mass number = 15.

    • Neutrons = 15 - 7 = 8 → Symbol: N₇¹⁵.

  3. Chlorine Isotope: Atomic Number = 17, Mass number = 37.

    • Neutrons = 37 - 17 = 20 → Symbol: Cl₁₇³⁷.

Average Atomic Mass

  • Atomic Mass: Average of all isotopes of an element.

    • Calculated as a weighted average based on the relative abundance of each isotope:
      ( ext{Average Atomic Mass}) = rac{ ext{(Mass of isotope 1)} imes ( ext{Relative abundance 1}) + ( ext{Mass of isotope 2)} imes ( ext{Relative abundance 2}) + ext{…}}{ ext{Total relative abundance}}

    • Example: Carbon's average atomic mass on the periodic table represents a weighted value based on the isotopes' relative abundances.

Summary of Key Concepts

  • Protons and neutrons reside in the nucleus, contributing to the mass of the atom.

  • Electrons orbit the nucleus, are significantly smaller, and define chemical behavior.

  • Atomic number = Number of protons, while atomic mass is an average derived from isotopes.