- 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 3: A Tour of the Periodic Table
Figure 4-4. Representative Box from the Periodic Table
There are usually four main components in each box on the periodic table: atomic number, average atomic mass, element symbol, and element name. The box for carbon is shown here. In this example, the atomic number, 6, is in the top left corner. The average atomic mass, 12.011, is in the bottom right corner. The element symbol, C, is in the center, and the element name, carbon, is directly below the symbol. There are slight variations in the exact location of each component depending on the version of the table. A quick way to tell the atomic number and average atomic mass apart is that the atomic number is always a whole number, and the average atomic mass is usually written with at least a few decimal places of precision, unless it is an unstable radioactive element.
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The periodic table is made up of boxes for each unique element arranged in 18 columns, called "groups" or "families," and seven rows, called "periods." As of 2012, the official periodic table released by IUPAC contains 114 total named elements with flerovium and livermorium as the most recent additions. Every bit of matter in the universe is made of the elements on the periodic table. The naturally occurring elements are all found in the first 92 boxes. Amazingly, by the mid-20th century, scientists were able to produce new elements in the laboratory by combining two naturally occurring elements in a nuclear reactor. Unit 4 video illustrates how scientists at Lawrence Livermore National Laboratory in California combine the nuclei of two naturally occurring elements to produce larger and larger elements. In theory, the table is limitless and only depends on how well scientists are able to create new elements in the laboratory.
Each box on the periodic table tells us important information about the element it represents. Nearly all periodic tables will have these four core pieces of information in each box: the name of the element, the atomic number of the element, the one- or two-letter symbol for the element, and the atomic mass of the element. (Figure 4-4) Other periodic tables may try to cram even more information about their properties into the box. This can serve two purposes: one is to have an easy location for collecting information about the elements; the other is to visualize the patterns of the elements on the periodic table. However, different periodic table designers will put that information in different locations inside the box.
More than two-thirds of elements are metals, including sodium, lead, uranium, iron, and zinc. They tend to be solid at room temperature, have shiny or reflective surfaces, and are excellent conductors of heat and electricity. Metals are also highly malleable, which means that we can hammer them into new shapes; this is how gold can be hammered out into thin sheets called "gold leaf." Other properties of metals come over large ranges; for example, metals can have very different densities, which is the amount of mass they have per unit volume. Sodium has such a low density that it floats in water, whereas the metal lead is one of the densest of all the elements; it quickly sinks in water. A small piece of lead would be extremely heavy to hold. (Figure 4-5)
Figure 4-5. Metals Can Have a Wide Range of Densities
On the left, a small piece of sodium floats in water. On the right, one bar of lead weighs 42 pounds.
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Non-metals vary greatly in their physical properties. For example, some non-metals are gases at room temperature, some are solids, and one, bromine, is a liquid. Non-metals that are solid tend to be brittle, dull, and poor conductors of heat and electricity. Some gaseous non-metals, including hydrogen, oxygen, and nitrogen, occur as diatomic elements, which means they are found in nature in pairs: H2, O2, and N2. This contrasts with the noble gases like argon and neon, which are monatomic and exist just as Ar or Ne atoms in nature. All non-metals range greatly in color, from reddish bromine to yellow sulfur. The non-metallic elements are essential to life on Earth: Carbon, hydrogen, oxygen, and nitrogen comprise most organic molecules, often with smaller amounts of phosphorus and sulfur.
Semi-Metals or Metalloids
Semi-metals or metalloids are the elements that comprise the boundary between metals and non-metals, so they include the typical properties of metals and non-metals. When we see semi-metals like silicon or antimony, they look almost metallic, but are brittle. Semi-metals have low conductivity at cooler temperatures, but high conductivity at warmer temperatures. Because of this, the most common semi-metal, silicon, is used in electronic devices, as it strictly controls the flow of electricity.
Let's consider three common elements: carbon (a non-metal), silicon (a semi-metal), and copper (a metal). On any given day, we probably see each of these in their elemental forms, or at least we're very close to them. Pure elemental carbon comes in two major forms in nature: diamond and graphite. Diamonds are one of the hardest materials in nature; we can see them in jewelry and drill bits. Graphite, on the other hand, is the technical name for pencil lead. In addition to being a common writing tool, it is an industrial lubricant. Pure silicon is around us all the time, as it is found in the chips inside electronics, including computers and cell phones. Lastly, copper metal, with its reddish brown color, is also found in many electronics, as it is the most common material in wires, because it conducts electricity so well. We also see it on the outer coating of pennies.