Silver is a transition metal, known by its chemical symbol Ag, which originates from the Latin word argentum. It is positioned in Group 11 and Period 5 of the periodic table, placing it among the noble metals alongside copper and gold. Silver’s unique properties, from its lustrous appearance to its unparalleled electrical performance, are defined by precise, fundamental numerical constants. These numbers quantify silver’s identity, behavior in the physical world, and interactions in chemical systems.
Defining Atomic Numbers
The fundamental identity of silver is established by its atomic number (Z), which is 47. This number signifies that every atom of silver contains 47 protons within its nucleus. For a neutral silver atom, this count also equals the number of electrons orbiting the nucleus.
The standard atomic weight of silver is 107.868 atomic mass units (amu). This value represents a weighted average of the naturally occurring isotopes, primarily Silver-107 and Silver-109. Since these isotopes exist in nearly equal abundance, the resulting atomic mass is almost exactly halfway between their mass numbers.
The arrangement of the 47 electrons dictates the element’s chemical behavior, described by its electron configuration: \([\text{Kr}]4d^{10}5s^1\). The configuration shows that silver has a completely filled \(4d\) subshell and a single electron in the outermost \(5s\) orbital. This specific structure, which gives silver only one valence electron, is a major factor in its conductivity and its tendency to form a \(+1\) ion.
Physical State Constants
The bulk properties of silver are defined by several physical state constants, starting with its density. At room temperature, pure silver has a density of \(10.49\) grams per cubic centimeter (\(g/cm^3\)). This high value indicates that silver is a relatively heavy metal, with a mass more than ten times that of water for the same volume.
Silver remains solid across a wide temperature range, defined by its melting and boiling points. Its melting point is \(961.8^\circ C\) (\(1235\) K). The boiling point, where liquid silver transitions into a gas, occurs at \(2162^\circ C\) (\(2435\) K). This significant difference allows silver to maintain its structural integrity as a liquid across a vast temperature range, which is fundamental to applications like soldering, casting, and alloying.
Electrical and Thermal Performance Metrics
Silver’s ability to transport energy is quantified by its electrical and thermal performance metrics. The electrical conductivity of silver is approximately \(6.30 \times 10^7\) Siemens per meter (\(S/m\)) at room temperature. This value is the highest of any known metal, establishing silver as the theoretical standard for electrical conduction.
The corresponding electrical resistivity, the inverse of conductivity, is a low \(1.6 \times 10^{-8}\) ohm-meters (\(\Omega \cdot m\)). Copper has a conductivity that is approximately \(97\%\) of silver’s value, while gold is about \(65\%\) as conductive. Silver’s superior performance is attributed to its unique electron configuration, which minimizes the resistance electrons encounter as they move through the metal’s crystal lattice.
Silver also excels in thermal conduction, with a specific thermal conductivity value of approximately \(429\) Watts per meter-Kelvin (\(W/(m\cdot K)\)). This number is the highest among all pure metals, meaning silver transfers heat energy most efficiently. This makes the element ideal for heat dissipation in specialized high-performance electronics.
Chemical Interaction Numbers
The chemical behavior of silver is governed by its oxidation states, which define the electrical charge an atom acquires when forming compounds. Silver’s primary and most stable oxidation state is \(+1\). This positive charge results from the atom readily losing the single electron in its outermost \(5s\) orbital.
While \(+1\) is standard, silver can also exhibit a \(+2\) state in highly oxidizing compounds, such as silver(II) fluoride. A \(+3\) oxidation state is known but is extremely rare and requires powerful oxidizing agents to achieve. These higher numbers demonstrate the potential for more complex chemical interactions under specialized conditions.
The standard reduction potential for the \(Ag^+/Ag\) half-cell is \(+0.80\) Volts (V). This positive voltage indicates that the silver ion (\(Ag^+\)) has a strong tendency to gain an electron and become neutral silver metal. This high potential is why silver is considered a noble metal and is relatively resistant to oxidation compared to metals like copper.