Chapter 5

The Periodic Law

Objectives

Explain the roles of Mendeleev and Moseley in the development of the periodic table.

Describe the modern periodic table.

Explain how the periodic law can be used to predict the physical and chemical properties of elements.

Describe how the elements belonging to a group of the periodic table are interrelated in terms of atomic number.

  1. Sections 5-1 (History of the Periodic Table)
    1. Mendeleev and the Chemical Periodicity
      1. No one knew how to accurately determine the mass of an atom.
      2. Held a conference and made a decision on how to calculate the mass of an atom.
      3. Dmitri Mendeleev was writing a textbook and decided to input the new information.
      4. Organized the elements based on the new atomic masses.
    2. A new and better pattern was discovered
      1. Henry Moseley (1911) discovered more patterns by organizing the elements by their atomic numbers
      2. Discovered the Periodic Law- the physical and chemical properties of the elements are periodic functions of their atomic numbers.
  2. The Modern Periodic table
    1. Is an arrangement of the elements in order of their atomic number so that the elements with similar properties fall in the same column, or group
      1. Metals
        1. Alkali metals
        2. Alkaline earth metals
        3. Transition metals
        4. Other metals
      2. Metalliods
        1. Semiconductors
      3. Non-metals
        1. Halogens
        2. Other nonmetals
        3. Noble gases

    Objectives

    Define atomic and ionic radii, ionization energy, electron affinity, and electronegativity.

    Compare the periodic trends of atomic radii, ionization energy,a nd electronegativity, and state the reasons for these variations.

    Define valence electrons, and state how many are present in atoms of each main-group element.

    Compare the atomic radii, ionization energies, and electronegativities of the d-block elements with those of the main-group elements.

  3. Section 5-3 (Electron configuration and Periodic Properties.
    1. Atomic Radii-
      1. Definition- may be defined as one-half the distance between the nuclei of identical atoms that are bonded together.
        1. Period trends-a gradual decrease in atomic radii from left to right.
        2. Group trends- a general increase in the atomic radii of the main group elements as you go down.
    2. Ionization energy
      1. Ionization- the process of producing an ion.
      2. Ionization energy-the energy required to remove one electron from a neutral atom of an element.
        1. Period trends- ionizations energies of the main-group elements increase across each period.
        2. Group trends-Among the main-group elements, ionization energies generally decrease down the groups.
      3. Removing electrons form Positive ions
        1. Electrons can be removed from positive ions
        2. Is known as the second ionization energy
    3. Electron Affinity
      1. Definition-the energy change that occurs when an electron is acquired by a neutral atom.
        1. Period trends-generally increases as move across.
          1. Exceptions group 2
          2. Exceptions group 4
        2. Group trends- generally electrons add with greater difficulty down a group
      2. Adding Electrons to Negative ions
        1. The second electron affinities are all positive.
        2. Never occurs for halogens
    4. Ionic radii
      1. Types of ions
        1. Cation- a positive ion
        2. Anion- a negative ion
      2. Period trends-
        1. Cations- decrease across the period
        2. Anions-
          1. Take a big jump
          2. Decrease across the period.
    5. Valence electrons- The electrons available to be lost, gained or shared in the formation of chemical compounds.
      1. Are in the outer shell
      2. Follow group numbers except to d-shell electrons
    6. Electronegativity
      1. Definition-is a measure of the ability of an atom in a chemical compound to attract electrons.
        1. Period trends- tend to increase across each period, with some exceptions
        2. Group trends- decrease down or remain the same