Chemical Nomenclature, Elements and Symbols Help (page 2)
Before standard element symbols and the Periodic Table were invented, discussing matter was a guessing game. Early scientists located in laboratories far distant from each other and speaking different languages had problems communicating. Cultural and language differences had a big impact on the naming of elements.
Additionally, just as ancient words and phrases are no longer part of today’s spoken languages, like “thee” and “thou” of old English, some element names originated from seldom used languages. The ancient name for copper is cuprum , which is why the symbol for copper is Cu. Scientists, confused by outdated names, needed a standard method that everyone used.
Nicknames added to the confusion. For example, baking soda used to make breads rise is actually sodium bicarbonate, but most people don’t call it that. Battery acid, the liquid that allows electricity to be mysteriously generated in cars, is really sulfuric acid. Household laundry bleach is usually known as sodium hypochlorite by chemists. Or do you know anyone who says, “Please pass the sodium chloride,” at a meal?
Common names for elements don’t provide accurate descriptions of elemental components. In fact, there are so many compounds and combinations of chemicals that sometimes figuring out what someone is talking about takes longer than the experiment!
For thousands of years, people have known about the basic elements. They knew rocks were hard, water was liquid, and fog was a mist. They knew materials could be heated, packed down, frozen, and altered in different ways, while others could not. What they didn’t understand was how matter seemed to turn from one form into another. Rust was a mystery. Explanations, based more on ancient myth than science, provided a path to understanding.
As time went on, scientists began to concentrate on the study of individual elements, but they still had a problem. Because in different languages chemical elements were known by different names, scientists couldn’t always be sure they were talking about the same thing. Just as a traveler, not knowing the language, has problems in foreign countries asking directions or finding a hotel, early chemists had problems comparing results and analyzing compounds that no one seemed to recognize. For example, the element, iron, is called Eisen in German, Piombo in Italian, Olovo in Czech, and Fer in French. Scientists, too busy with their experiments to study languages, ran into trouble when they tried to communicate their findings to colleagues in other parts of the world. To give you an idea of the problem, Table 4.1 provides a sampling of element names in different languages.
It was obvious that some sort of common code or chemical nomenclature was needed.
Chemical nomenclature is the standardized system used to name chemical compounds.
Symbols, at first based on Latin words, were used as an elemental code because writing the full name was time consuming. The powerful insecticide dichlorodiphenyltrichloroethane, or DDT, is written as (C 6 H 4 Cl) 2 CHCCl 3 with Berzelius’ method. If it weren’t for this shorthand code so much time would be taken up writing the samples’ names that there wouldn’t be any time left to do the experiment!
Chemical shorthand becomes especially important when writing chemical reactions. The symbol for an element can be one letter as in carbon (C) and phosphorus (P), two letters as in strontium (Sr) and molybdenum (Mo), or three letters as in the more recent elements in the Periodic Table such as ununquadium (Uuq) and ununoctium (Uuo). Notice that when an element has more than a one letter shorthand name, only the first letter of the symbol name is capitalized.
In 1862, the French geologist Antoine Béguyer de Chancourtois made up a list of elements, arranged by increasing atomic weight. He is said to have wrapped the list, divided into 16 sections around a cylinder. After he had done this, he noticed that different sets of similar elements lined up. One of these groups, oxygen, sulfur, selenium, and tellurium, had a repeated pattern. The atomic weights of these elements are 16, 32, 79, and 128, all multiples of 16. This periodic repeat seemed to be part of a natural pattern that occurred regularly.
Atomic weight is not to be confused with atomic number . Atomic number is written as the superscript of an element on the Periodic Table, while the atomic weight is written as a subscript. The atomic weight of boron is 10.81 while its atomic number is 5.
Atomic number (Z) equals the number of protons in the nucleus of an atom.
Around this same time, English chemist John Newlands, Professor of Chemistry at the School of Medicine for Women in London, was also overlapping elements and seeing similarities. With a repeat of chemical groups every eight elements, Newlands, a jazzy kind of guy, was reminded of eight-note music intervals and called his findings the Octave rule . Members of the Royal Chemical Society, not into music composition, ignored Newlands’ work for many years.
Meyer: The Modern Theory of Chemistry
In 1864, Die Modernen Theorien der Chemie (The Modern Theory of Chemistry) was published by German chemist Lothar Meyer. Meyer used the atomic weight of elements to arrange twenty-eight elements into six families with similar chemical and physical characteristics. Sometimes elements seemed to skip a predicted weight. Where he had questions, he left spaces for possible elements. Meyer also used the word valence to describe the number that equals the combining power of one element with the atoms of another element. He thought this combination of characteristic grouping and valence was responsible for the connection between families of elements.
After seeing a recurring pattern of peaks and valleys when plotting atomic weight, Meyer thought these patterns seemed to make up family rhythms. When he measured the volume of one atomic weight’s worth of an element with the same number of atoms in the sample, Meyer decided the measurements must stand for the same amounts of each distinct atom.
Figure 4.1 illustrates Meyer’s experimental results with a recurring pattern in one family. If you start with the element at the top of each peak, you find lithium, sodium, potassium, rubidium, and cesium lined up by atomic number and weight.
Unlike Newlands’ octaves, Meyer’s data showed the groups were not the same length. He was one of the first chemists to notice that the group lengths changed. Hydrogen was in a group by itself, lithium through fluorine made another group, sodium through chlorine made another, potassium through bromine, rubium through iodine, and others. The groups started out small and then became larger.
Meyer saw repeating periods of atomic volume, but they changed in size. The first period contained only hydrogen and was one period in length. The second and third periods had seven elements. The fourth and fifth periods were seventeen elements in length. Meyer’s work held until the inert gases were discovered, then an extra element was added to each period, to give periods of 2, 8, 8, 18, and 18.
Medeleyev: On the Relation of the Properties to the Atomic Weights of Elements
Five years later, working separately, Russian chemist Dimitri Mendeleyev and Meyer arranged the elements into seven columns relative to the elements’ known physical and chemical properties. The differences in their work were slight, but each added to the current knowledge.
Mendeleyev presented a scientifically significant table of elements in his paper On the Relation of the Properties to the Atomic Weights of the Elements , which the Russian Chemical Society praised. In his paper, Mendeleyev discussed the periodic resemblance between chemical groups with respect to similar reactions.
As it turns out, many of the gaps Mendeleyev made spaces for in his periodic chart turned out to be correct placeholders for elements discovered later. Initially, titanium (Ti) was placed next to calcium (Ca), but this would have placed it in group III with aluminum (Al). However, since studies of titanium’s properties showed that it was more like silicon (Si) than aluminum, Mendeleyev left a space next to calcium and eventually placed Ti in group IV with silicon.
Ten years later in 1879, Swedish chemist Lars Nilson discovered the missing element with properties in between calcium (atomic weight of 40) and titanium (atomic weight of 48) and named it scandium (Sc). Scandium has an atomic weight of 45.
Figure 4.2 shows some of the characteristics of the element titanium.
In 1870, Meyer’s next generation Periodic Table of 57 elements was published. This table, including properties such as melting point , added depth to the understanding of interactions and the role of atomic weight at that time. Meyer additionally studied the atomic volume of elements to fine tune his placement of elements into particular groups.
Perhaps Meyer’s curiosity came from the fact that he grew up in a family of physicians and was exposed to scientific and medical discussions for much of his early life. His initial schooling in Switzerland was in the field of medicine. The many elements in the body and their complex interactions gave Meyer much to think about. Table 4.2 shows a few of the most common elements and their functions in the body.
Meyer’s initial chemistry research grew out of his fascination with the physiology of respiration. He was one of the first scientists to recognize that oxygen combined with hemoglobin in the blood. Then, in order to explain specific biochemical processes and systems, he found he had to identify the elements more completely.
The modern Periodic Table contains around 118 elements. Those up through atomic number 92 (uranium) are naturally occurring, whereas the “transuranic” elements, those synthesized in heavy-nuclei interactions, make up the most recent discoveries. Some new elements’ symbols, like in the time of Meyer and Mendeleyev, represent gaps or spaces for elements that seem to be hinted at by test data. When compared to Mendeleyev’s and Meyer’s early tables, the details described over 150 years ago are amazingly accurate.