- Online Text
- 1. Introduction
- 2. History of the Periodic Table
- 3. A Tour of the Periodic Table
- 4. Atomic Mass, Atomic Number, and Carbon-12
- 5. The Orbital Structure of the Atom
- 6. Electron Configurations
- 7. Effective Nuclear Charge and Size
- 8. Ionization Energy and Ionic Radius
- 9. Forming Compounds
- 10. Electronegativity
- 11. Naming Compounds
- 12. Conclusion
- 13. Further Reading
- Unit Guide (PDF)
Section 1: Introduction
The periodic table is a blueprint for all the known elements in the universe. Everything that makes up the food we eat, the air we breathe, and the ground we stand on can be found within the seven rows and 18 columns of the periodic table. The periodic table is widely used and scientifically approved, and no chemist can do work without one. Impressively, even with the major shift in thinking following the development of quantum mechanics, the general structure of the periodic table has not changed much since 1869. (Figure 4-1) It allows those with the appropriate knowledge to unlock the secrets of the elements, including their average mass, relative reactivity, and internal organization. How can this one document tell us so much?
Figure 4-1. The Periodic Table
As of 2012, the periodic table contains 118 confirmed chemical elements. Of these elements, 114 have been officially recognized and named by the International Union of Pure and Applied Chemistry (IUPAC). The elements that start with "Uu" are not officially recognized.
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The table is organized by atomic number, which is the number of protons in the nucleus. We can organize the periodic table this way because all atoms of a specific element have the same number of protons. In fact, if the number of protons were to change, the atom's identity would change. In addition to the atomic number, there are many patterns within the periodic table. In this unit, we will discuss some of those patterns, including electron configuration, size, and reactivity. We also will examine how these patterns allow us to predict the formation of compounds.
In addition to chemical properties, the periodic table reveals the cultural history of each element. Some elements have countries in their names (francium, polonium, and germanium), while others bear the names of notable scientists (einsteinium, nobelium, and curium). The discoverers of these elements named them in honor of home countries or to commemorate other influential scientists. The periodic table contains a wealth of information, once we know how to interpret it.
The naming of elements turned out to be one of the last battlegrounds of the Cold War. In the 1960s, research groups in the Soviet Union and the United States simultaneously claimed discovery of elements 104 and 105. The International Union of Pure and Applied Chemistry, or IUPAC, the global organization charged with establishing standard practices for chemists, is responsible for handing out naming rights to labs in honor of discovering the element. Only after the end of the Cold War, in 1997, did IUPAC settle the dispute between the Americans and Soviets. Americans won the rights to name element 104 after Ernest Rutherford (rutherfordium), and the Russians won the rights to name element 105 (dubnium) after Dubna, the town in Russia where the element was discovered.