The gold atom (Au) is a dense and highly valued noble metal. A neutral atom of gold possesses exactly 79 electrons, which perfectly balances the positive charge of the protons in its nucleus.
Determining the Electron Count in Neutral Gold
The total count of electrons in any neutral atom is directly determined by its atomic number (Z). Gold’s position on the periodic table assigns it the atomic number 79, which represents the fixed quantity of protons found within the nucleus. In an electrically neutral atom, the number of negatively charged electrons must precisely match the number of positively charged protons. Therefore, a neutral gold atom contains 79 electrons to maintain a net zero charge.
Electron Shell Arrangement
These 79 electrons are organized into distinct energy levels, or shells, around the nucleus. This arrangement follows a specific pattern known as the electron configuration. For gold, this configuration is complex, involving a distribution of \(2, 8, 18, 32, 18, 1\) electrons across its six major shells, written in spectroscopic notation as \([Xe] 4f^{14} 5d^{10} 6s^{1}\).
The outermost shell, the \(6s\) orbital, contains only a single electron, which is the atom’s valence electron. This single electron is primarily responsible for how the gold atom interacts with other elements. The \(5d\) orbital, positioned just below the valence shell, is completely filled with 10 electrons, contributing significantly to gold’s chemical stability. This organization is an exception to general filling rules, driven by the stability of a completely filled \(5d\) subshell.
Electrons in Gold Ions
The electron count of a gold atom changes when it forms an ion by gaining or losing electrons during a chemical reaction. The most common charged states, or oxidation states, for gold are \(+1\) and \(+3\).
When gold forms a gold(I) ion (\(\text{Au}^+\)), it loses its single outermost electron from the \(6s\) orbital. The resulting \(\text{Au}^+\) ion retains 78 electrons (79 minus 1). The gold(III) ion (\(\text{Au}^{3+}\)) is formed by removing three electrons: the single \(6s\) electron and two electrons from the inner \(5d\) orbital. This highly charged ion contains 76 electrons and is also very stable in chemical compounds.
How Electron Structure Creates Gold’s Properties
The unique electron configuration of gold is directly responsible for its most recognizable properties, including its distinctive color and resistance to corrosion. For most metals, electron transitions occur in the ultraviolet range, resulting in a silvery-gray appearance. In gold, however, the energy difference between the filled \(5d\) orbitals and the partially filled \(6s\) orbital is shifted.
This energy shift is caused by relativistic effects, a phenomenon noticeable in heavy elements like gold. The innermost electrons move so fast that their mass increases, causing their orbitals to contract and influencing the energy of the outer electrons. This effect causes gold to absorb blue light and reflect the remaining wavelengths, which the human eye perceives as the characteristic metallic yellow color. Furthermore, the tight binding of the single \(6s\) electron, also a result of relativistic contraction, contributes to gold’s chemical inertness by making it less available for bonding.
Electron Shell Arrangement
These 79 electrons are not randomly scattered but are organized into distinct energy levels, or shells, around the nucleus. The arrangement follows a specific pattern, known as the electron configuration, which for gold is exceptionally complex, involving a final distribution of \(2, 8, 18, 32, 18, 1\) electrons across its six major shells. This detailed configuration is written in spectroscopic notation as \([Xe] 4f^{14} 5d^{10} 6s^{1}\).
The outermost shell, the \(6s\) orbital, contains only a single electron, which is the atom’s valence electron. This single \(6s\) electron is primarily responsible for how the gold atom interacts with other elements. The \(5d\) orbital, which is positioned just below the valence shell, is completely filled with 10 electrons, contributing significantly to gold’s chemical stability. This specific organization is an exception to the general filling rules for elements due to the stability gained from having a completely filled \(5d\) subshell.
Electrons in Gold Ions
The electron count of a gold atom changes when it participates in a chemical reaction and forms an ion. An ion is a charged atom that has gained or lost one or more electrons to achieve greater stability. The most common charged states, or oxidation states, for gold are \(+1\) and \(+3\).
When gold forms a gold(I) ion, symbolized as \(\text{Au}^+\), it loses its single outermost electron from the \(6s\) orbital. The resulting \(\text{Au}^+\) ion retains 78 electrons, calculated from 79 original electrons minus 1 lost electron. The gold(III) ion, \(\text{Au}^{3+}\), is formed by the removal of three electrons: the single \(6s\) electron and two electrons from the inner \(5d\) orbital. This more highly charged ion contains 76 electrons, which is a configuration that is also very stable in chemical compounds.
How Electron Structure Creates Gold’s Properties
The unique electron configuration of gold is directly responsible for its most recognizable properties, including its distinctive color and its resistance to corrosion. For most metals, the electron transitions that determine color happen in the ultraviolet range, resulting in a silvery-gray appearance. However, in gold, the energy difference between the filled \(5d\) orbitals and the partially filled \(6s\) orbital is shifted into the visible light spectrum.
This energy shift is caused by relativistic effects, a phenomenon that becomes noticeable in heavy elements like gold. The innermost electrons move so fast that their mass increases, causing their orbitals to contract and influencing the energy of the outer electrons. This effect causes gold to absorb blue light and reflect the remaining wavelengths, which the human eye perceives as the characteristic metallic yellow color. Furthermore, the tight binding of the single \(6s\) electron, also a result of relativistic contraction, makes it less available for chemical bonding, which contributes to gold’s well-known chemical inertness.