L1- The Periodic Table

Learning Objectives of the Periodic Table

  • State the periodic law and explain the organization of elements in the periodic table.

  • Predict the general properties of elements based on their location within the periodic table.

  • Identify metals, nonmetals, and metalloids by their properties and/or location on the periodic table.

Historical Context of the Periodic Table

  • Early chemists discovered that various elements could be grouped based on similar chemical behaviors.

    • Example grouping:

    • Lithium (Li), Sodium (Na), and Potassium (K)

      • Common properties: shiny, good conductors of heat and electricity, reactive.

    • Second grouping:

    • Calcium (Ca), Strontium (Sr), and Barium (Ba)

      • Similar in being shiny and good conductors, but distinctly different reactivities and compound formations.

      • Li, Na, and K form compounds with oxygen in a ratio of two atoms to one oxygen atom, whereas Ca, Sr, and Ba form compounds with a one-to-one atom ratio.

    • Another grouping includes Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I), exhibiting similar properties but differing significantly from the aforementioned groups.

Development of the Periodic Table

  • Dimitri Mendeleev (1869) and Lothar Meyer (1870) recognized a periodic relationship among known elements.

    • Both published tables arranged according to increasing atomic mass.

    • Mendeleev's contribution: utilized his table for predicting unknown elements that would have properties similar to known elements like aluminum and silicon.

    • Support through discovery of Gallium (1875) and Germanium (1886) supported Mendeleev’s predictions.

  • By the 20th century, it was established that the periodic relationship involved atomic numbers rather than atomic masses.

    • Modern Periodic Law: states that the properties of elements are periodic functions of their atomic numbers.

  • A modern periodic table:

    • Arranged in increasing order of atomic numbers.

    • Groups atoms with similar properties in the same vertical column (groups).

Structure of the Modern Periodic Table

  • The table consists of:

    • 7 Horizontal Rows (Periods or Series)

    • 18 Vertical Columns (Groups)

  • Each box in the table displays:

    • Atomic number

    • Symbol

    • Average atomic mass

    • Sometimes the name of the element.

  • Groups labeled traditionally with capital letters but recommended to use numbers 1-18 (IUPAC standard).

  • For compactness, parts of two rows are usually situated below the main body (elements in this part are known as lanthanides and actinides).

Classifications Within The Periodic Table

  • Elements classified based on shared physical and chemical properties:

    • Metals (shiny, malleable, ductile, good conductors of heat and electricity)—Shaded Yellow

    • Example: Magnesium, Iron.

    • Nonmetals (dull, poor conductors)—Shaded Green

    • Example: Carbon, Oxygen.

    • Metalloids (intermediate properties)—Shaded Purple

    • Example: Silicon, Boron.

Specific Groups and Their Properties

  • Elements categorized into subclasses based on properties and compound formation:

    • Main-group elements (or representative elements)—Columns 1, 2, and 13-18.

    • Transition Metals—Columns 3-12.

    • Inner Transition Metals—Rows at the bottom of the table.

    • Lanthanides (Top Row)

    • Actinides (Bottom Row)

  • Notable groups include:

    • Alkali Metals (Group 1, except H)—Form compounds with one atom of the element and one atom of hydrogen.

    • Alkaline Earth Metals (Group 2)—Form compounds with one atom of the element and two atoms of hydrogen.

    • Pnictogens (Group 15), Chalcogens (Group 16), Halogens (Group 17), Noble Gases (Group 18).

Unique Element: Hydrogen

  • Hydrogen shows characteristics of both groups 1 and 17 due to unique properties, thus can be shown at the top of both or separately.

Practical Applications of the Periodic Table

  • Similar properties in groups have significant implications in natural sciences and medicine.

    • Example: Gertrude Elion's work with sulfur and oxygen (both in Group 16) in DNA structure alteration.

    • This led to the use of sulfur-based compounds in interrupting cell replication, crucial for cancer treatments.

    • Resulting treatments for leukemia and changes in drug development methodologies earned them the Nobel Prize in 1988.

Atomic Mass Documentation

  • Some elements have atomic masses shown in square brackets:

    • Common in elements composed entirely of unstable, radioactive isotopes (e.g., Element 43: Technetium, Element 61: Promethium).

    • The number in square brackets represents the atomic mass number of the most stable isotope.