The Element Zinc
An Introduction to the Element Zinc
Zinc is an element that has been known scientifically for some time, and has seen use throughout history. Today, zinc remains a critical element for the functioning of modern technology and human biology.
10 Interesting & Fun Facts about Zinc
- Brass is an alloy of zinc and copper, and was one of the most important metal compounds in ancient times.
- Zinc is used in a variety of everyday products, including paint, shampoo, and deodorant.
- Scientists today use the different isotopes of zinc to study food webs and ecosystems, almost like carbon dating!
- U.S. pennies are made mostly of zinc – only the thin outer coating is made of copper.
- Zinc is the 24th most common element in the Earth’s crust, about 0.01%.
- The name zinc comes from the German word zinke meaning “prong” or “tooth.”
- Zinc deficiency affects more than 2 billion people worldwide, making it an important part of global health goals.
- Diethyl zinc was the first known compound to contain a carbon-metal sigma bond.
- Zinc refinement poses environmental risks, as it releases sulfur dioxide.
- The common cold is actually treatable with zinc supplements.
The Element Zinc on the Periodic Table
Zinc, atomic symbol Zn, has atomic number 30 and is the last fourth-period transition metal. It lies to the right of copper and the left of gallium, and is above cadmium. It has an electron configuration of [Ar]4s2 3d10.
Zinc is one of the few transition metals with only one major oxidation state: +2. While it technically can form the +1 state, this configuration is extremely unstable and difficult to maintain. With an electronegativity of 1.65 on the Pauling scale, the element readily bonds with most electronegative nonmetals, including oxygen, chlorine, and nitrogen.
Zinc in Electrochemistry
Within the field of electrochemistry, some elements get a lot of attention. Well-behaved and electrically reactive elements are useful in the construction of galvanic cells – zinc is perfect for this purpose because it’s abundant and easily oxidized (reduction potential of -0.76V). Zn/Cu cells are the most commonly seen when studying basic electrochemistry. Just like in this scientific context, the electrochemical properties of zinc are what make it so useful in the real world, as we’ll discuss later.
Zinc in the Body
Zinc is one of the most important metals in the body. It is critical to the functioning of about 10% of the proteins in our body, playing a role in cell signaling, gene expression, and apoptosis (controlled cell death). On the macro scale, zinc is important for proper immune function and digestion, as well as growth in children.
Zinc has been shown as a useful treatment for a variety of ailments. Besides the common cold, zinc helps those suffering from anorexia to gain weight, in addition to preventing macular degeneration (the process of losing eyesight as one ages). This element is a cheap and effective way of improving health, especially in the developing world where deficiency is common.
Zinc Applications in Today’s World
Defense from the Elements (literally)
One of the biggest threats to public infrastructure is rusting. Due to salts, water, or plain old air, exposed iron and steel degrade over time, leaving transportation networks and large buildings unreliable. Zinc helps us by preventing this oxidation. The primary application of zinc today is as a sacrificial anode. Coating iron or steel in a layer of zinc (called galvanization) will prevent the metal underneath from oxidizing (rusting) because the zinc is more “willing” to be oxidized than the metal it coats. Much of the exposed metal we see on a day-to-day basis, including in fences, bridges, roofs, and car bodies, is protected by this thin layer of metal Zn.
In addition to physically coating a metal surface, zinc can offer electrochemical protection through a wire. Exposed and inaccessible metal surfaces like underground pipelines and ship hulls are often protected by zinc, which replaces the electrons lost by oxidation. The structural integrity of the modern world is thanks in no small part to zinc.
Besides infrastructure, zinc’s ease of oxidation is employed in batteries. Since they are just galvanic cells, the characteristics that we saw earlier make it perfect as an anode in disposable batteries. Powder of the metal is used as the reducing agent – the white paste that sometimes leaks out of old batteries is often a mixture of this zinc along with graphite and other electrolytes.
Where is Zinc Found?
Zinc can be found across the world. Its main ore, sphalerite (ZnS), is quite common, often being mixed in with other sulfur-containing ores. China contributes the most to production, with Australian and Peruvian mining operations close behind.
When and How was the Element Discovered?
Zinc has been known for millennia and saw extensive use across the ancient world. Alloys of zinc, especially brass (Zn + Cu), were employed by a variety of old civilizations – Judean brass has been found dating back to the 14th century BCE.
Zinc was isolated in India around 1300 CE. It was imported to the West after this, but scientific study of the metal wouldn’t begin in earnest for several hundred years. The Swiss physician Paracelsus was the first Westerner to identify the element as a unique metal around 1526. Its name derives from the German zinke, or tooth, owing to the needle-like structure of the pure metal. In the centuries following, various Europeans contributed to the study of the element. The brothers William and John Champion discovered new and efficient ways of purifying zinc, which would see use for many years.
In the late 18th century, Luigi Galvani used zinc in his experiments which paved the way for modern electricity. His friend, Alessandro Volta, used the now-classic combination of zinc and copper to create a powerful but primitive battery, then called the Voltaic pile. The titles of the galvanic cell and the process of galvanization both honor Galvani’s work. Volta’s legacy is carried on in the very unit of electric potential, the Volt.
It took until the twentieth century for zinc’s biological importance to be discovered. Nowadays it is recognized as a key player in the structure and function of enzymes.
Transition metals nearing the end of the d-block flout the traditional rules of electron configuration. In their ionic states, these metals will often keep their d-orbital electrons in favor of losing their s-orbital electrons. This is why copper, silver, and gold all have +1 oxidation states. For the same reason, zinc will (almost) always lose its s-electrons rather than its d-electrons, giving it a +2 oxidation state. Chemically speaking, this makes it behave very similarly to an alkaline earth element, like calcium or magnesium. The electron configuration of a Zn2+ ion is [Ar]3d10, the same as calcium if you ignore the d-shell electrons.
While it is technically possible to have a +1 oxidation state, this form is unstable. Much like mercury, the ionic dimer Zn22+ is preferred. Without careful stabilization, this ion decomposes into Zn2+ and zinc metal. For all intents and purposes, this element is only found in the +2 oxidation state.
Being an electropositive metal, zinc is easily oxidized by many elements. Samples of the metal will be quickly coated in a layer of ZnO when exposed to oxygen gas, following the reaction 2Zn (s) + O2 (g) → 2ZnO (s).
The metal can react with water at high temperatures to form ZnO and hydrogen gas: Zn (s) + H2O (g) → ZnO (s) + H2 (g).
It also reacts with sulfur, producing a green flame.
This compound is the primary zinc supplement used today. It supplies free zinc to be used in the body, and is both cheap and easy to produce.
ZnCl2 is a very common and useful form of this element. It is useful as a flux and drying agent, although there are more efficient options. It is also used in organic chemistry as a Lewis acid, being a common alternative to AlCl3 in the Friedel-Crafts reaction.
Zn(OH)2 is used in medicine as a surgical dressing to promote healing. It is also the byproduct of a common process used to detect zinc minerals.
ZnS is used primarily for its interactions with light. Most glow-in-the-dark pigments are ZnS with trace amounts of another metal. The classic greenish glow-in-the-dark color comes from ZnS doped with copper. Manganese and silver are used to make orange and blue colors respectively. In addition to its phosphorescent properties, ZnS is used in pigments like lithopone, one of the most common white pigments. ZnS is also a photocatalyst, meaning it can allow some reactions to occur in the presence of light, including the formation of hydrogen gas from water.
Last but not least, zinc oxide is a key player in existing and emerging technologies. It is used in the production of vulcanized rubber, an essential material. It is also very useful for its properties as a semiconductor. New technologies such as thin-film transistors and spintronics as well as novel LED and LCD displays rely on a ZnO medium to function. Additionally, ZnO shows promise as an anode in lithium-ion batteries, being more efficient and environmentally friendly than traditional materials like cobalt. Zinc oxide can also be used in microfibers to generate electricity, opening the door to electrically self-sufficient nanomachines.
Isolation of Zinc
Zinc ores like sphalerite are mined across the world. Once collected, these materials are finely ground and then separated by making use of the differences in their hydrophobicity. Once separated out, the ore (mostly ZnS at this stage) is roasted, converting it to ZnO. From there, it is either reduced to Zn metal by carbon and carbon monoxide, or isolated by electrolysis following treatment with sulfuric acid. It is worth noting that the roasting step, converting ZnS to ZnO, releases oxides of sulfur which are detrimental to the environment. Refinement therefore proposes some challenges as the world moves towards greener and more zinc-reliant practices.
Unfortunately, there is no efficient and practical way to isolate this element in a laboratory setting.
- Symbol: Zn
- Melting point: 419.5 °C
- Boiling point: 907.0 °C
- Density: 7.14 g/cm3
- Atomic weight: 65.38 Da
- Atomic number: 30
- Electronegativity: 1.65
- Classification: Transition metal
- Natural abundance in earth’s crust: 0.0075% or 75ppm
- Electron configuration: [Ar] 4s2 3d10
- Isotopes: 64Zn, 66Zn, 67Zn, 68Zn, 70Zn
- Naturally found in the minerals sphalerite (zinc sulfide), smithsonite (zinc carbonate), and hemimorphite (zinc silicate)
- Toxicity: Toxic in excess, leading to copper and iron deficiency. Swallowing/digestion of U.S. pennies is very dangerous due to high zinc content.
Where can I buy Zinc?
Zinc metal can be purchased from a variety of online and physical retailers, including Amazon and Home Depot. Zinc supplements are available at virtually every pharmacy or drug store.