natural abundance

Examples of natural abundance in the following topics:

• Average Atomic Mass

  • The average atomic mass of an element is the sum of the masses of its isotopes, each multiplied by its natural abundance.
  • Average atomic mass = f1M1 + f2M2 + ... + fnMn where f is the fraction representing the natural abundance of the isotope and M is the mass number (weight) of the isotope.
  • When data are available regarding the natural abundance of various isotopes of an element, it is simple to calculate the average atomic mass.
  • Another example is to calculate the atomic mass of boron (B), which has two isotopes: B-10 with 19.9% natural abundance, and B-11 with 80.1% abundance.
  • Calculate the average atomic mass of an element given its isotopes and their natural abundance

• Isotopes

  • The five peaks in this spectrum demonstrate clearly that natural bromine consists of a nearly 50:50 mixture of isotopes having atomic masses of 79 and 81 amu respectively.
  • The center and right hand spectra show that chlorine is also composed of two isotopes, the more abundant having a mass of 35 amu, and the minor isotope a mass 37 amu.
  • In the case of methylene chloride, the molecular ion consists of three peaks at m/z=84, 86 & 88 amu, and their diminishing intensities may be calculated from the natural abundances given above.
  • Two other common elements having useful isotope signatures are carbon, 13C is 1.1% natural abundance, and sulfur, 33S and 34S are 0.76% and 4.22% natural abundance respectively.

• Mass Spectrometry to Measure Mass

  • Chloride atoms and ions come in two isotopes, with masses of approximately 35 amu (at a natural abundance of about 75 percent) and approximately 37 amu (at a natural abundance of about 25 percent).
  • The streams of sorted ions pass from the analyzer to the detector, which records the relative abundance of each ion type.

• Properties of Carbon

  • Carbon has very diverse physical and chemical properties due to the nature of its bonding.
  • Interestingly, carbon allotropes span a wide range of physical properties: diamond is the hardest naturally occurring substance, and graphite is one of the softest known substances.
  • Carbon has two stable, naturally occurring isotopes: carbon-12 and carbon-13.
  • It has a very low natural abundance (0.0000000001%), and decays to 14N through beta decay.

• Isotopes of Hydrogen

  • Hydrogen has three naturally occurring isotopes: protium, deuterium and tritium.
  • Hydrogen has three naturally occurring isotopes: 1H (protium), 2H (deuterium), and 3H (tritium).
  • Other highly unstable nuclei (4H to 7H) have been synthesized in the laboratory, but do not occur in nature.
  • 1H is the most common hydrogen isotope with an abundance of more than 99.98%.
  • It has a natural abundance of ~156.25 ppm in the oceans, and accounts for approximately 0.0156% of all hydrogen found on earth.

• Elemental Boron

  • As a result, it is a low-abundance element in both the solar system and the Earth's crust.
  • Natural boron is composed of two stable isotopes: 11B is more abundant than 10B, which has a number of uses as a neutron-capturing agent.
  • On Earth, boron is concentrated by the water-solubility of its more common naturally-occurring compounds, the borate minerals.
  • Chemically uncombined boron, which is classified as a metalloid, is not found naturally on Earth.
  • Boric acid is mildly antimicrobial, and a natural, boron-containing, organic antibiotic does exist.

• Properties of Hydrogen

  • It is highly abundant and has unique and important chemical properties.
  • Hydrogen is the most abundant chemical substance in the universe, especially in stars and gas giant planets.
  • Hydrogen naturally exists as three isotopes, denoted 1H, 2H, and 3H. 1H occurs at 99.98 percent abundance and has the formal name protium. 2H is known as deuterium and contains one electron, one proton, and one neutron (mass number = 2).

• Characteristics of Mass Spectra

  • A mass spectrum will usually be presented as a vertical bar graph, in which each bar represents an ion having a specific mass-to-charge ratio (m/z) and the length of the bar indicates the relative abundance of the ion.
  • The most intense ion is assigned an abundance of 100, and it is referred to as the base peak.
  • The molecular ion of propane also has m/z=44, but it is not the most abundant ion in the spectrum.
  • Both distributions are observed, but the larger ethyl cation (m/z=29) is the most abundant, possibly because its size affords greater charge dispersal.

• Elements and Compounds

  • Of these 118 known elements, only the first 98 are known to occur naturally on Earth.
  • Hydrogen and helium are by far the most abundant elements in the universe.
  • However, iron is the most abundant element (by mass) in the composition of the Earth, and oxygen is the most common element in the layer that is the Earth's crust.
  • Pure samples of isolated elements are uncommon in nature.
  • The noble gases (e.g., neon) and noble metals (e.g., mercury) can also be found in their pure, non-bonded forms in nature.

• Iron, Cobalt, Copper, Nickel, and Zinc

  • Copper is the most heavily used of the coinage metals due to its electrical properties, its abundance (compared to silver and gold), and the properties of its brass and bronze alloys.
  • Neither of these two metals appears uncombined in nature.
  • Iron, cobalt, and nickel are fairly good reducing agents, so they rarely appear uncombined in nature.
  • At the temperatures characteristic of the Earth's core, iron and nickel form a giant natural magnet which creates the Earth's magnetic field.
  • Like nickel, cobalt in the Earth's crust is found only in chemically combined form, save for small deposits found in alloys of natural meteoric iron.