chapter3

3.1 Internal Structure of an Atom

  • Subatomic Particles: The fundamental building blocks of atoms.

    • Electrons:

      • Located outside the nucleus.

      • Negative electrical charge (-1).

      • Smallest mass among subatomic particles (9.109 x 10^-28 g).

    • Protons:

      • Found in the nucleus.

      • Positive charge (+1), equal in magnitude to the electron’s charge.

      • Mass of 1.673 x 10^-24 g.

    • Neutrons:

      • Also found in the nucleus.

      • No charge (0).

      • Mass virtually the same as a proton (1.675 x 10^-24 g).

3.2 Atomic Number and Mass Number

  • Atomic Number (Z):

    • Number of protons in an atom's nucleus.

  • Mass Number (A):

    • Sum of the number of protons and neutrons in the nucleus.

  • Element:

    • A pure substance in which all atoms have the same atomic number.

    • Atoms with the same atomic number share the same chemical properties.

3.3 Isotopes and Atomic Masses

  • Isotopes:

    • Atoms of the same element with the same number of protons and electrons but different numbers of neutrons.

    • Example: Sodium has isotopes with mass numbers 23 (11 protons, 12 neutrons) and 24 (11 protons, 13 neutrons).

  • Most elements occur naturally as mixtures of isotopes.

    • Atomic Mass:

      • Calculated based on isotopic abundance and mass.

    • Example calculation for Carbon:

      • 98.89% of 12C contributes 12 amu and 1.11% of 13C contributes 13.0034 amu, leading to an average atomic mass of 12.01 amu.

3.4 The Periodic Law and the Periodic Table

  • Periodic Law:

    • Properties of elements are periodic functions of their atomic numbers.

  • Periodic Table:

    • Arranged in order of increasing atomic number with similar properties in vertical columns (groups).

    • Periods: Horizontal rows; Groups: Vertical columns.

3.5 Metals and Nonmetals

  • Metals:

    • Characteristics: luster, thermal/electrical conductivity, malleability.

    • High electrical conductivity, though it decreases as temperature increases.

    • Typically solid at room temperature.

  • Nonmetals:

    • Lack the properties of metals; can exist as solids, liquids, or gases.

    • Poor electrical conductivity and mostly brittle solids.

3.6 Electron Arrangements Within Atoms

  • Electron Shells:

    • Regions around the nucleus containing electrons with similar energy.

    • Electrons in first shell are closer and have lower energy than those in higher shells.

  • Subshells:

    • Regions within a shell containing electrons with the same energy:

      • s holds 2, p holds 6, d holds 10, f holds 14 electrons.

  • Orbitals:

    • Specific regions within subshells where electrons are most likely found.

    • Each orbital can hold a maximum of 2 electrons with opposite spins.

3.7 Electron Configurations and Orbital Diagrams

  • Electron Configuration:

    • The distribution of electrons among the subshells for an atom.

    • Example for oxygen: 1s² 2s² 2p⁴.

  • Orbital Diagrams:

    • Visual representations of electrons in orbitals.

3.8 The Electronic Basis for the Periodic Law and the Periodic Table

  • Chemical Properties of Groups:

    • Elements in the same group share similar outer shell electron arrangements.

  • Last Electron Principle:

    • The last electron added to the configuration helps distinguish properties from the preceding element.

3.9 Classification of the Elements

  • Classification Schemes:

    • Based on physical properties and electron configurations.

      • Categories include metals, nonmetals, noble gases, representative, transition, and inner transition elements.