A group on the periodic table is a vertical column of elements whose atoms share a similar arrangement of outer electrons, giving them comparable chemical properties. This organization helps scientists categorize the 118 known elements into families that behave in predictable ways. Group 6 contains four metallic elements that possess distinctive high-strength characteristics. This collection is collectively known as the Chromium Group, named after the first and most well-known element in the series.
The Official Naming of Group 6
The International Union of Pure and Applied Chemistry (IUPAC) currently designates this column simply as Group 6. This modern numbering system runs from 1 to 18 across the table. The IUPAC standard was introduced to resolve confusion from two older, incompatible naming conventions that used Roman numerals and letters.
The older Chemical Abstract Service (CAS) system, common in the United States, labeled this column as Group VIB, while the older IUPAC system, favored in Europe, referred to it as Group VIA. The elements in this column are Chromium (Cr), Molybdenum (Mo), Tungsten (W), and the synthetic element Seaborgium (Sg). Naming the group after Chromium, the lightest and most abundant member, provides a simple, universal descriptor that bypasses the historical numbering conflicts.
Key Properties of the Chromium Group
The elements of the Chromium Group are all considered transition metals, meaning they occupy the d-block of the periodic table. A defining characteristic of these elements is their ability to exhibit multiple oxidation states, with the maximum state for the group being positive six (+6). This high valence capability allows them to form a wide array of stable compounds.
Chromium compounds in the +3 and +6 states are known for producing vivid, intense colors; for example, trace amounts of chromium ions give rubies their red hue. These metals are also classified as refractory metals because they are exceptionally resistant to heat and wear. Their strong metallic bonds result in very high melting points and high densities.
Tungsten, in particular, has the highest melting point of all known metals, reaching approximately 3414 degrees Celsius. The heaviest element, Seaborgium, is a synthetic element that exists only briefly in a laboratory setting, but trace studies confirm it shares the tendency to form stable compounds in the +6 oxidation state.
Practical Uses of Group 6 Elements
Chromium’s natural ability to form a thin layer of oxide on its surface makes it highly resistant to corrosion. This property is utilized extensively in creating stainless steel alloys and in chrome plating, which provides a durable finish to materials. Chromium is also used in the industrial tanning of leather.
Molybdenum is primarily used as an alloying agent to strengthen steel, improving its hardness and resistance to high temperatures. It is a frequent component in tool steels and high-strength parts for aircraft and missiles. Molybdenum compounds also function as catalysts in the petroleum industry, helping to refine crude oil.
Tungsten’s exceptional hardness and extreme heat resistance make it indispensable for applications involving intense friction or heat. It is used to manufacture the filaments in incandescent light bulbs and is a component in high-speed cutting tools and drill bits.