Coinage Metals: 3 Important Metals (Cu, Ag, Au)

A cluster of three pliable and flexible Transition Metals that belong to group 11 (previously known as IB) of the periodic table—Copper (Cu), Silver (Ag), and gold (Au)—are known as coinage metals. While bearing resemblance to alkali metals, the coinage metals exhibit significantly elevated ionization energies and higher standard electrode potentials, which are positively charged. The outer structure of these things’ electronic configurations is shown by how the electrons are arranged in the nd¹⁰(n+1)s¹ orbital configuration.

Consequently, coinage metals exhibit heightened resistance to oxidation and corrosion, rendering their oxidation process considerably more challenging. Furthermore, the presence of d-electrons in these elements contributes to their ability to exhibit variable valency, as evidenced by the formation of compounds such as Cu^I, Cu^II, Cu^III, Ag^I, Ag^II, Au^I, and Au^III. Additionally, these elements have the capacity to form a diverse array of coordination compounds. Transition elements are commonly categorized as such.

History of Coinage Metals

• The ancient world and post-medieval coins were primarily composed of coinage metals such as gold, silver, bronze, and copper.
• The origins of coins in Western history are commonly traced back to their inception around 700 BC, either slightly before or after, on Aegina Island. Alternatively, some sources suggest that coins were first introduced in Ephesus, Lydia, around 650 BC.
• During the 6th century BC, Ancient India emerged as a prominent pioneer in the field of coinage, establishing itself as one of the earliest civilizations to engage in this monetary practice on a global scale.
• Since that juncture, coins have emerged as the quintessential representation of currency across diverse societies.
• The initial coins were crafted from electrum, a naturally occurring pale yellow amalgamation of gold and silver, which was subsequently blended with silver and copper to form an alloy.
• Copper, silver, and gold represent the trio of metallic elements that currently serve as the primary constituents for the production of coins, thus earning the designation of “coinage metals” in contemporary parlance.

Coinage Metals

Copper (Cu)

Elemental Properties of Copper

Important Copper Minerals

Chemical Properties of Copper

The chemical properties of copper exhibit a wide range of characteristics. These attributes, in contrast to physical attributes, can solely be examined by subjecting copper to a range of chemical treatments. Copper, for example, exhibits a significantly low level of reactivity. When copper undergoes chemical reactions with other elements, it forms various compounds. Some examples of copper compounds include copper sulfate (CuSO₄), copper oxide (CuO), copper chloride (CuCl₂), and copper nitrate (Cu(NO₃)₂).

• Copper (II) chloride exhibits a +2 oxidation state in its metallic form. The substance exhibits a chemical reaction with aluminum foil, resulting in the generation of hydrogen gas, copper (I) oxide, and aluminum chloride. Consequently, it can be classified as a relatively gentle oxidizing agent.
• When CuCl₂ and NaOH are heated, they react to make sodium (II) hydroxide and release chlorine gas.
• The ionic states of copper that are most commonly observed are Cu⁺¹ and Cu⁺². When subjected to heat, the copper ion with a charge of +2 emits a vibrant green flame, while the copper ion with a charge of +1 emits a distinct blue flame.
• Because it is lower on the electromotive series than hydrogen, copper doesn’t dissolve in acids that change hydrogen into water. However, it does engage in reactions with oxidizing acids such as nitric acid and highly concentrated sulfuric acid when subjected to elevated temperatures.
• Copper exhibits remarkable resistance to the corrosive impact of atmospheric and aqueous environments. However, upon prolonged exposure to the atmosphere, a delicate green protective layer known as a patina develops, consisting of hydroxycarbonate, hydrosulfite, and small amounts of various other compounds.
• Copper can be classified as a moderately noble metal due to its inherent stability when exposed to dilute acids that lack oxidizing or complexing properties, provided there is no presence of air.
• The rapid dissolution of nitric acid and sulfuric acid occurs when oxygen is present. Highly stable cyanide complexes are generated upon dissolution, rendering them soluble in aqueous ammonia or potassium cyanide in the presence of oxygen.
• Cupric oxide (CuO) and cuprous oxide (Cu₂O) are made when the metal is heated in oxygen. This causes the metal to oxidize into these two different oxide compounds. The compound Cu₂S, also known as cuprous sulfide, is formed through the process of copper being subjected to heat in the presence of sulfur.

Gold (Au)

Elemental Properties of Gold

Important Gold Ores

Chemical Properties of Gold

• Gold is characterized by its relatively low reactivity, which imparts resistance to tarnishing, corrosion, and rusting.
• Gold is characterized by its inert nature, rendering it impervious to the corrosive effects of atmospheric oxygen, water, steam, and commonly encountered mineral acids.
• It is positioned beneath hydrogen in the electrochemical series, thus it does not exhibit the ability to displace hydrogen from dilute mineral acids such as hydrochloric acid (HCl), nitric acid (HNO₃), and sulfuric acid (H₂SO₄).
• The process of dissolving gold in aqua regia results in the formation of auric chloride. Aqua regia, a highly corrosive solution, is composed of three parts concentrated hydrochloric acid (HCl) and one part concentrated nitric acid (HNO₃).
• Over the course of millennia, gold has been a preferred material for jewelry and decorative applications due to its exceptional durability and remarkable resistance to environmental degradation.
• Gold exhibits a notably diminished reactivity towards a wide range of chemicals, acids, and gases, thereby substantiating its exceptional capacity to withstand corrosion and tarnishing.
• Gold is very good at conducting electricity, which makes it a good choice for use in electronic devices that need stable and long-lasting electrical connections. This is because gold is very resistant to corrosion.

Silver (Ag)

Elemental Properties of Silver

Important Silver Ores

Chemical Properties of Silver

• Despite being heated to the point of becoming red, silver exhibits no reactivity toward atmospheric oxygen.
• The initial ionization energy of silver exhibits the most favorable value when compared to the corresponding values of all other elements within Group 11.
• Silver exhibits a reactivity that falls within the spectrum delineated by copper and gold.
• Silver readily reacts with all four halogens to form halides, and exclusively with fluorine does it yield a dihalide.
• The prevailing oxidation states exhibited by silver are predominantly +1 and +2. The occurrence of the +3 state is infrequently observed.
• Due to its limited chemical reactivity, the substance exhibits infrequent reactions. However, it is noteworthy that nitric acid and highly concentrated sulfuric acid possess the capacity to initiate an attack on it.

Important Properties of Coinage Metals

Properties of Coinage Metals

• Coinage metals can be encountered in both their elemental form and in various compounds.
• These coinage metals exhibit notable characteristics such as hardness, malleability, ductility, and elevated melting points.
• These materials exhibit excellent thermal and electrical conductivity.
• The typical electronic configuration of coinage metals can be described as (n-1)d¹⁰ns¹. Similar to alkali metals, the atoms of these elements possess a solitary electron residing in the valence shell. In contrast, it is noteworthy that the penultimate shell of these elements harbors a total of 18 electrons, which stands in stark contrast to the mere 8 electrons found in the penultimate shell of alkali metals.
• Coinage metals, such as copper (Cu), silver (Ag), and gold (Au), exhibit characteristics that are significantly different from those of alkali metals. As an illustration, alkali metals exhibit pronounced reactivity, while silver and gold demonstrate a minimal inclination to engage in chemical reactions.
• In the context of coinage metals, it is observed that the penultimate d-orbitals, along with the s-electron of the valence shell, can undergo electron loss. This is due to the relatively small energy difference between the ns and (n-1)d electrons. As a result, coinage metals demonstrate a range of oxidation states.

Copper (Cu): +1 and +2 states, i.e., Cu+(I) and Cu++(II)

Silver (Ag): +1 state, i.e., Ag+

Gold (Au): +1 and +3 states, i.e., Au+ (I) and Au+3 (III)

• The coinage metals exhibit varying levels of reactivity. Copper exhibits a pronounced reactivity towards acids, while silver displays a comparatively lower level of reactivity. In contrast, gold exhibits the least reactivity when exposed to acids. Similarly, copper exhibits a vast array of salts, whereas the repertoire of salts for silver is relatively limited and the number of known salts for gold is exceedingly scarce.

The entirety of the coinage metals can be classified as intricate salts. To provide illustrations,

[Cu(NH3)4] SO4: Tetraamminecopper (II) Sulfate Monohydrate

Na[Ag(CN)2]: Sodium dicyanoargentate (I)

K[Au(CN)2]: Potassium dicyanoaurate (I)

Applications of Coinage Metals

• From a historical perspective, coinage metals have gained significant recognition due to their inherent monetary, decorative, and metallurgical attributes.
• The utilization of coinage metals, such as silver wire, is prevalent in the construction of electrical instruments.
• Copper, classified as one of the coinage metals, exhibits exceptional electrical conductivity. Consequently, it is employed in the fabrication of electric cables and electrical devices.
• The addition of minute amounts of gold and silver to copper results in a substantial increase in hardness. This resilient alloy is employed in the fabrication of decorative objects such as ornaments and idols, among other applications.

Some Other Coinage Metals

Video on Coinage Metals

References

• https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistry_(Petrucci_et_al.)/23%3A_The_Transition_Elements/23.6%3A_Group_11%3A_Copper_Silver_and_Gold
• https://www.pharmacy180.com/article/the-coinage-metals-1415/ Introduction: Coinage Metals in Organic SynthesisnBruce H. Lipshutz and Yoshinori Yamamoto
• https://www.wondriumdaily.com/the-coinage-metals-copper-silver-and-gold/
• https://www.vedantu.com/question-answer/the-coinage-metals-are-a-iron-cobalt-nickel-b-class-10-chemistry-cbse-605cc883665c295f802508cb
• https://chemistnotes.com/inorganic/coinage-metals-cu-ag-au-definition-important-properties-and-4-uses/