CHM1045 UNIT 1PT1

Introduction to Atomic Structure

  • Overview of fundamental concepts: atoms, elements, and the periodic table

Definitions

  • Atom: The smallest unit of an element that retains its chemical properties.

  • Element: A pure substance consisting entirely of one type of atom.

Carbon in the Periodic Table

  • Carbon is represented with the symbol C and has an atomic number of 6.

  • Atomic number (Z): This represents the number of protons in an atom. For carbon, Z = 6.

  • Atomic mass (A): This number represents the total number of protons and neutrons in the atom.

  • Additional context: An element consists entirely of one type of atom, exemplified by carbon.

Structure of the Atom

  • Atoms consist of three types of subatomic particles:

    • Protons (p+): Positively charged particles found in the nucleus.

    • Neutrons (n0): Neutral particles, also located in the nucleus.

    • Electrons (e-): Negatively charged particles that orbit the nucleus.

  • Charge summary:

    • Protons: +1 charge

    • Neutrons: 0 charge

    • Electrons: -1 charge

Mass of Subatomic Particles

  • Mass in Atomic Mass Units (amu):

    • Protons and neutrons are defined to have a mass of 1 amu each.

    • Electrons have a mass approximately equal to 0 (specifically 1.6 x 10-27 kg).

    • Mass of protons and neutrons: 1.67 x 10-27 kg each.

    • Significance of electron mass: negligible in atomic mass calculations.

Calculating Atomic Mass

  • Atomic mass can be calculated using:

    • Atomic mass (A) = Number of protons + Number of neutrons

  • When calculating: round atomic masses to whole numbers for simplicity.

  • Example Calculation for Carbon (C):

    • Atomic number = 6 (protons)

    • Assume atomic mass = 12

    • Neutrons = Atomic mass - Atomic number = 12 - 6 = 6

Identifying Elements using the Periodic Table

  • Changing atomic number (number of protons) changes the element.

    • Example:

    • Atomic number 6 (C) has 6 protons.

    • Atomic number 7 (N) has 7 protons.

  • Protons define the chemical identity of the element, while the number of neutrons can vary.

Neutral Atoms

  • Atoms are neutral when they have an equal number of protons and electrons.

  • Example of neutrality in carbon:

    • Atomic number of carbon (C) is 6.

    • Therefore, carbon has 6 protons and 6 electrons to maintain neutrality.

  • Neutrons can be calculated by subtracting the atomic number from the atomic mass.

Isotopes

  • Isotopes are variants of the same element with different numbers of neutrons.

  • Notation for isotopes:

    • Can be represented as ACZ (where A is the atomic mass and Z is the atomic number).

    • Example for Oxygen isotopes:

    • 16O8 (8 protons, 8 neutrons)

    • 18O8 (8 protons, 10 neutrons)

  • The same atomic number implies the same number of protons, but different atomic masses indicate different neutron counts, affecting mass.

Summary of Key Points

  • Atomic number -> Number of protons; defines the element.

  • Atomic mass -> Sum of protons and neutrons.

  • Protons and electrons define charge; similar number means neutrality.

  • Isotopes have the same protons (same element), but differing neutrons.

Practical Applications

  • Understanding atomic structure aids in elucidating chemical reactions, bonding, and the behavior of materials.

  • Awareness of isotopes is critical in fields such as medicine (e.g., radiotherapy) and environmental science (e.g., dating methods).