Periodic Table and Trends

Terminology of Periodic Table

  • Periodic Table Review
    • Historical Context:
    • Dmitri Mendeleev, a Russian Chemist, developed the first periodic table in 1861.
    • Organizational Characteristics:
    • Grouped elements by common properties.
    • Arranged elements by atomic weight.
    • Unique Contributions:
    • Mendeleev uniquely predicted unknown elements that were later discovered, demonstrating the predictive power of his periodic table.
    • Example: Discovery of magnesium by Moseley.

Periodic Law

  • Definition:
    • The physical and chemical properties of the elements are periodic functions of their atomic numbers.

Structure of the Periodic Table

  • Vertical Columns:
    • Called groups.
    • Two numbering systems to label groups:
    • IUPAC numbering system.
  • Horizontal Rows:
    • Called periods.

Connection to Atomic Structure

  • Group:
    • Represents the number of valence electrons in the atoms of the group.
  • Period:
    • Represents the number of energy levels in the atoms of the period.

Effective Nuclear Charge (Zeff)

  • Equation for Effective Nuclear Charge: Zeff=Z−SZ_{eff} = Z - S
    • Where:
    • $Z$ = number of protons (atomic number).
    • $S$ = number of inner shell core electrons (core electrons).
  • Trends:
    • Across a period: Increases as protons are added to the nucleus, leading to a stronger pull on electrons.
    • Down a group: Decreases as the inner shell electrons increase, reducing the effective nuclear charge felt by outer electrons.

Atomic Radius

  • Definition:
    • The atomic radius is defined as one-half the distance between the nuclei of identical atoms in the solid state.
  • Trends:
    • Down a group: Increases due to the addition of energy levels, which places outer electrons further from the nucleus.
    • Across a period: Decreases as protons are added to the nucleus, increasing the nuclear charge and pulling electrons closer.

Ionization Energy

  • Definition:
    • The minimum energy required to remove an electron from an atom in its gaseous state.
  • Trends:
    • Down a group: Decreases because the outermost valence electrons are in higher energy levels that are farther from the nucleus.
    • Across a period: Increases as the nuclear charge holds the electrons more tightly, requiring more energy to remove one.

Electron Affinity

  • Definition:
    • The energy change that occurs when an atom gains an electron.
  • Trends:
    • Across a period: Increases in energy due to a greater tendency to accept electrons as more electrons are gained.

Types of Elements and Their Properties

  • Metals:
    • Found on the left side of the periodic table.
    • Properties include high electrical conductivity, malleability, and ductility.
  • Nonmetals:
    • Found on the top right of the periodic table along the staircase line.
    • Properties include poor conductivity and varied states of matter.
  • Metalloids:
    • Positioned around the staircase line, having properties intermediate between metals and nonmetals.
  • Transition Metals:
    • Groups 3-12, characterized by their ability to form variable valencies and colored compounds.
  • Alkali Metals:
    • Group 1, highly reactive with one valence electron.
  • Alkaline Earth Metals:
    • Group 2, less reactive than alkali metals with two valence electrons.
  • Halogens:
    • Group 17, very reactive nonmetals that can exist in all three states of matter.
  • Noble Gases:
    • Group 18, known for their inertness, having a full valence shell.

Ion Formation

  • Cations:
    • Positively charged ions formed by the loss of electrons.
    • Characteristic: Their size decreases compared to the original atom due to a greater effective nuclear charge.
  • Anions:
    • Negatively charged ions formed by the gain of electrons.
    • Characteristic: Their size increases compared to the original atom due to increased electron-electron repulsion.

Ionization Energies of Elements

  • Element Z:

    • Ionization Energies (kJ/mol):
    • First: 580
    • Second: 1,815
    • Third: 2,740
    • Fourth: 11,600
    • Fifth: 14,800
    • Conclusion: Element Z has 3 valence electrons.

  • Element W:

    • Ionization Energies (kJ/mol):
    • First: 520
    • Second: 729
    • Third: 2,740
    • Fourth: 11,600
    • Fifth: 14,800
    • Conclusion: Element W has higher ionization energies, indicating stronger hold on its electrons after losing 2 electrons, likely having 5 valence electrons.