Overview
This lecture covers the history and development of the periodic table, focusing on Dmitri Mendeleev’s contributions and the structure of the modern table.
Mendeleev’s Life and Achievements
- Dmitri Mendeleev overcame personal hardships and poverty to study at a university in St. Petersburg.
- Mendeleev was driven by a sense of duty and passion for scientific discovery.
- He revolutionized chemistry by organizing elements based on repeating (periodic) patterns in their properties.
Creation and Structure of the Periodic Table
- In the 1860s, about 60 elements were known, and they were first arranged by atomic weight.
- Mendeleev noticed that certain properties repeated at regular intervals when elements were ordered by atomic weight.
- He left gaps in his table for elements not yet discovered and predicted their properties accurately.
- The periodic table organizes elements into periods (rows) and groups (columns) with similar chemical properties.
Groups of the Periodic Table
- Alkali metals (far left): Soft, shiny, very reactive metals; form +1 ions.
- Alkaline earth metals: Reactive metals; form +2 ions, less reactive than alkali metals.
- Transition metals (center): Typical metals like iron and gold; good conductors, malleable, and mostly similar to each other.
- Halogens (right, next to noble gases): Very reactive nonmetals; form -1 ions and react with metals.
- Noble gases (far right): Unreactive gases discovered after Mendeleev's time.
- Lanthanides and actinides (bottom): Metals with similar properties, difficult to separate, placed separately for space.
Significance and Evolution of the Periodic Table
- Mendeleev’s table set the stage for future discoveries and guided chemists for decades.
- Other scientists developed alternative table designs, like de Chancourtois’ cylindrical version, but Mendeleev's became standard.
- The periodic table’s arrangement is ultimately based on atomic structure and electrons, not atomic weight.
Key Terms & Definitions
- Periodic Table — Organized chart of elements showing recurring patterns in properties.
- Periodicity — The repeating pattern of element properties across periods (rows).
- Atomic Weight — The average mass of an element’s atoms, initially used to order elements.
- Ion — Atom or molecule with a net electric charge (positive: cation, negative: anion).
- Alkali Metals — Group 1, highly reactive metals.
- Alkaline Earth Metals — Group 2, reactive metals with two positive charges.
- Transition Metals — Elements in the center of the table, typical metals.
- Halogens — Highly reactive nonmetal group forming -1 ions.
- Noble Gases — Unreactive gases found in Group 18.
- Lanthanides/Actinides — Rare earth and radioactive metals, shown separately.
Action Items / Next Steps
- Review the different groups of the periodic table and their properties.
- Prepare for upcoming lessons on atomic structure and the role of electrons.