Group 16: The Oxygen Family
The Oxygen Family, also called the chalcogens, consists of the elements found in Group 16 of the periodic table and is considered part of the Main Group elements. It consists of the elements oxygen, sulfur, selenium, tellurium and polonium. These can be found in nature in both free and combined states.
Properties and Periodic Trends
All elements of the oxygen family have 6 electrons in their outermost shell. The electron configurations for each element are shown below.
Note: The electron configuration can be written in Noble Gas Notation, a shorthand option. This can be done by using the Noble Gas that comes before the element, putting it in brackets, and continuing the electron notation from there.
Ex. Polonium can be written as [Xe] 6s2 4f14 5d10 6p4
As one moves down the group, metallic character increases, with tellurium being a metalloid and polonium a metal. Melting point, boiling point, density, atomic radius, and ionic radius all increase going down the group. Ionization energy decreases going down the group. The most common oxidation state is -2, however sulfur can also exist at a +4 and +6 state and +2, +4, and +6 oxidation states are possible for Se, Te, and Po.
Individual Properties of Each Element
Oxygen is a gas at room temperature and 1 atm, and is colorless, odorless, and tasteless. It is the most abundant element by mass in both the Earth's crust and the human body. It is second to nitrogen as the most abundant element in the atmosphere. There are many commercial uses for oxygen gas, which is typically obtained through the process of fractional distillation. It is used in the manufacture of iron, steel, and other chemical manufacturing. It is also used in water treatment, as an oxidizer in rocket fuel, for medicinal purposes, and in petroleum refining.
Oxygen has two allotropes: O2 and O3. In general, O2, or dioxygen, is the form referred to when talking about the elemental or molecular form because it is the normal form of the element. The O2 bond is very strong, and oxygen can also form strong bonds with other elements. However, compounds that contain oxygen are considered to be more thermodynamically stable than O2.
The latter allotrope, ozone, is a pale-blue poisonous gas with a strong odor. It is a very good oxidizing agent, stronger than dioxygen, and can be used as a substitute for chlorine in purifying drinking water without giving the water an odd taste. However, because of its unstable nature it disappears and leaves the water unprotected from bacteria. Ozone at very high altitudes in the atmosphere is responsible for protecting the Earth's surface from ultraviolet radiation; however, at lower altitudes it becomes a major component of smog.
Its primary oxidation states are -2, -1, 0 and -1/2 in O2-, but -2 is by far the most common oxidation state. Typically, compounds that have oxygen in the oxidation state of two are referred to as oxides. When oxygen reacts with metals, it forms oxides that are mostly ionic in nature. These can dissolve in water and react to form hydroxides, which is why they can be called basic anhydrides or basic oxides. Nonmetal oxides, which form covalent bonds, are simple molecules with low melting and boiling points.
Compounds that contain oxygen with an oxidation state of -1 are referred to as peroxides. Examples of this type of compound are Na2O2 and BaO2. Because oxygen has an oxidation state of -1/2 in O2-, it is called a superoxide ion.
Oxygen is rarely featured as the central atom in a structure and can never have more than 4 elements bonded to it due to its small size and its inability to create an expanded valence shell. When it reacts with hydrogen, it forms water, which is extensively hydrogen-bonded, has a large dipole moment and is considered an universal solvent.
There are a wide variety of oxygen-containing compounds, both organic and inorganic, including oxides, peroxides and superoxides, alcohols, phenols, ethers, and carbonyl-containing compounds such as aldehydes, ketones, esters, amides, carbonates, carbamates, carboxylic acids and anhydrides.
Sulfur (Sulphur in British English)
Sulfur is a solid at room temperature and 1 atm pressure. It is usually yellow, tasteless, and almost odorless. It is the sixteenth most abundant element in Earth's crust. It exists in a variety of forms naturally, including elemental sulfur, sulfides, sulfates, and organosulfur compounds. Since the 1890s, sulfur has been mined using the Frasch process, which is useful for recovering sulfer from deposits that are under water or quicksand. However, in the modern age, there is a growing concern over sulfur emissions from industrial processes. Sulfur produced from this process is used in a variety of ways including in vulcanizing rubber and as fungicide to protect grapes and strawberries.
Sulfur is very unique in its ability to form a wide range of allotropes, more than any other element in the periodic table. The most common state for sulfur to be in is the solid S8 ring, as this is the most thermodynamically stable form at room temperature. Sulfur exists in the gaseous form in five different forms (S, S2, S4, S6, and S8). In order for sulfur to get to these states one must apply a sufficient amount of heat.
Two very common oxides of sulfur are sulfur dioxide (SO2) and sulfur trioxide (SO3). Sulfur dioxide is formed when sulfur is combusted in the air, which produces a toxic gas hat has a strong odor. These two compounds are used in the production of sulfuric acid, which can be used in a variety of reactions. Sulfuric acid is one of the top manufactured chemicals in the US, and is primarily used in the manufacture of fertilizers.
Sulfur also exhibits a wide range of oxidation states, with values ranging from -2 to +6. It is often the central ion in a compound and can easily hold up to 6 atoms around itself. When in the presence of hydrogen it forms the compound hydrogen sulfide, H2S, which is a poisonous gas, without hydrogen bonds and a very small dipole moment. Hydrogen sulfide can easily be recognized by its strong odor that is similar to that of rotten eggs, but this smell can be detected and low, nontoxic concentrations. This reaction with hydrogen epitomizes how different oxygen and sulfur act despite their common valence electron configuration and common nonmetallic properties.
A very large variety of sulfur-containing compounds exist, many of them being organic. The prefix thio- in from of the name of an oxygen-containing compound means that the oxygen atom has been substituted with a sulfur atom. General categories of sulfur-containing compounds include thiols (mercaptans), thiophenols, organic sulfides (thioethers), disulfides, thiocarbonyls, thioesters, sulfoxides, sulfonyls, sulfamides, sulfonic acids, sulfonates, and sulfates.
Selenium can be seen as a red or black amorphous, or a red or grey crystaline structure, which is its most stable structure. Selenium has properties very similar to those of sulfur, however, it is more metallic even though it is still classified as a nonmetal. It acts as a semiconductor and therefore is often used in the manufacture of rectifiers, which are devices that convert alternating currents to direct currents. Selenium also has photoconductivity, which means that in the presence of light the electrical conductivity of selenium increases. It is also used in the drums of laser printers and copiers. In addition, it has found increased use now that lead has been removed from plumbing brasses.
It is rare to find selenium in its elemental form in nature, and so typically it must be removed through a refining process, usually involving copper. It can often be found in soils and in plant tissues that have bioaccumulated the element. In large doses, the element is toxic, however many animals require it as an essential micronutrient. Selenium atoms are found in the enzyme glutathione peroxidase, which destroys lipid-damaging peroxides. For humans, it is an essential cofactor in maintaining the function of one's thyroid gland. In addition, some research has shown there to be a correlation between selenium-deficient soils and an increased risk of contracting the HIV/AIDS virus.
Tellurium is the metalloid of the Oxygen family, with a silvery white color and a metallic luster similar to tin at room temperature. Like selenium, it is also displays photoconductivity. It is an extremely rare element, and is most commonly found as a telluride of gold. It is often used in metallurgy in combination with copper, lead, and iron. In addition, it is used in solar panels and memory chips for computers. It is not toxic or carcinogenic, however when humans get exposed to too much of it they develop a garlic-like breath.
Polonium is a very rare, radioactive metal. There are 33 different isotopes of the element and all of the isotopes are radioactive. It exists in a variety of states, and has two metallic allotropes. It dissolves easily into dilute acids. It does not exist in nature in compounds, however it can be manipulated to form ones synthetically in the lab. It is used as an alloy with beryllium to act as a neutron source for nuclear weapons.
It is a highly toxic element. The radiation it emits makes it very dangerous to handle. It can be immediately lethal when applied at the correct dosage, or cause cancer if long-term exposure to the radiation occurs. Methods to treat humans who have been contaminated with polonium are still being researched, and it has been shown that chelation agents could possible help to decontaminate humans.
1. What properties increase going down the Oxygen family?
A: Melting point, boiling point, density, atomic radius, and ionic radius
2. What element can form the most allotropes in the periodic table?
3. What is photoconductivity and which elements display this property?
A: Photoconductivity is when the electrical conductivity of an element increases in the presence of light. Both selenium and tellurium display this property.
4. True or False. Ozone (O3) is a contributor to smog.
5. How many electrons do elements of the Oxygen family have in their outermost shell?
6. What does the term "peroxide" refer to?
A: A compound that contains oxygen in the oxidation state of -1.
7. How many elements in the Oxygen Family are metals, and which one(s)?
A: 1; Polonium.
8. What is the most common oxidation state for elements in the Oxygen Family?
9. What is the most abundant element by mass in the Earth's crust and in the human body?
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