Chemistry

The Chemical Properties of Gold



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Gold jewelry was buried along with the mummified bodies of Egyptian pharaohs. Johnny Depp had to wear gold caps on his teeth for his role in the Pirates of the Caribbean. From tombs to teeth, gold can be found. People would sell gold, hoard gold, wear gold, and even drink gold. Due to their desire to produce gold out of cheaper metals, alchemists lived their whole lives seeking the Philosopher's stone. Due to the discovery of gold, many countries have been colonized. And due to gold, prospectors face and endure the bitter winters of Alaska. Why gold? The answer lies in its chemical properties. Let's examine two of them, reactivity and heat of fusion.

Reactivity

The reactivity of an element can be indicated by its valence electron potential. Valence electrons are electrons that are located in the outermost shell of an atom. In chemical reactions, the elements share or exchange their valence electrons. The sharing or transfer of electrons, however, takes energy. Peculiarly, elements seems to act like people when it comes to their valence electrons. If it takes too much energy to share or transfer valence electrons, it would be difficult to carry out a chemical reaction. Gold has a high valence electron potential, with an estimated value of 51. It does not react with air, it ignores water, and it is stoic in the face acids and bases. Pure sodium, on the other hand, explodes in air and water. Sodium's valence electron potential is estimated to be only 14, less than one-third of gold's.

Gold, however, is not the element with the highest valence electron potential. The noble gases, like Neon and Helium, have extremely high valence electron potentials that, up until now, the values are still unknown. Neon and Helium are inert. They don't react at all. Gold, on the other hand, would react with halogens, such as chlorine and bromine, with some alkalis, such as cesium, and with a few select compounds, like cyanide. The selective reactivity of gold prevents it from being tarnished or discolored. The ancient Egyptians probably observed that the shiny golden color of this metal never fades. Thus, even without knowing about valence electrons, they viewed gold as a symbol of eternal wealth. They might as well take the gold with them into their graves.

Heat of Fusion



"Fusion" is a term that means two things. When a solid melts into liquid, it undergoes fusion. When a liquid freezes into solid, it also undergoes fusion. Fusion involves energy. For example, when ice melts, it absorbs energy and when liquid water freezes, it releases energy. The scientists discovered that the amount of heat energy needed to melt a certain mass of ice is equal to the amount of heat energy released to freeze the same mass of water. They might as well call that energy as the heat of fusion. Some scientists would like to fancy up the term and call it "enthalpy of fusion." Other scientists simply wanted to refer to it as "specific melting heat." Whichever term is used, they all mean the same.

The molar heat of fusion is the amount of thermal energy that must be absorbed or released by one mole of a substance to change its phase from solid to liquid or from liquid to solid. The molar heat of fusion of gold is 12.55 kJ/mol (kiloJoules per mole). This is more than twice the molar heat of fusion of water, which is only about 6 kJ/mol. The high heat of fusion of gold means that it would not easily melt. In fact, the melting point of gold is 1,948.57 degrees Fahrenheit or 1,064.76 degrees Celsius. The boiling point is 4,900 degrees Fahrenheit or 2,700 degrees Celsius. This means that gold cannot just disappear by melting or by evaporating. Gold appears to be indestructible. This is probably why gold is the chemical element that is found in the vaults of the Federal Reserve Bank of New York.

Of course, there is a way to dissolve gold, and perhaps hide it. All that is needed is a mixture of three parts hydrochloric acid and one part nitric acid. This mixture is named "aqua regia."

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