Oxygen is composed of 8 protons, and in its most common form with 8 neutrons, giving it an atomic weight of 16 (16 O) - this is know as a 'light' oxygen. It is called 'light' because a small fraction of oxygen atoms have 2 extra neutrons and a resulting atomic weight of 18 ( 18 O), which is then known as 'heavy' oxygen. In nuclear physics, nuclei are said to be mirrors when one has a certain number of neutrons and protons and the other has a reversed amount, such as the 3:8 ratio of neutrons to protons in oxygen-11 as compared to the 8:3 ratio in lithium-11. “When talking about mirror nuclei, we expect a sort of symmetry to hold,” Webb said. Oxygen-16 is composed of 8 protons, 8 neutrons, and 8 electrons. Oxygen, whose atomic number is eight, has three stable isotopes: 16O, 17O, and 18O. Explain what this means in terms of the number of protons and neutrons.
- Element Oxygen Neutrons
- Electron Energy Levels
- Oxygen Neutrons Electrons
- Oxygen Neutrons Protons Electrons
- Neutrons Oxygen-18 Atom
- What Is Oxygen Neutrons
- Sodium Neutrons
Stable Isotopes and IsotopeStratigraphy as Indicators of Changing Climate andBiosphere
While most oxgen atoms have a mass of 16 (8protons and 8 neutrons), a small number of oxygen atoms have a massof 18 (8 protons and 10 neutrons). Both of these isotopes are stable;they do not undergo radioactive decay.
Water molecules (H2O)in the ocean may contain either isotope, oxygen 16 or oxygen 18.Water molecules containing oxygen 18 are heavier (18 atomic massunits vs. 20 atomic mass units since each hydrogen atom has a mass ofjust one).
Element Oxygen Neutrons
Just as it is harder to throw a heavy objectinto the air than a light one, it is easier for water moleculescontaining the lighter oxygen 16 atoms to evaporate than the heavieroxygen 18 containing water molecules (the heavier ones need morekinetic energy to go into the gaseous state). In other words, aswater evaporates from the ocean surface a disproportionately largeamount of H2O-16is evaporated compared to H2O-18. Therefore, the ratio of H2O-18to H2O-16in clouds formed from that evaporation is less ('lighter') than thatin the seawater from which it evaporated.
Electron Energy Levels
If the moisture in those clouds falls as snowon a continent, and if that snow accumulates into an expandingcontinental ice sheet, then more and more isotopically lightH2Owill be stored on the continent and the remaining seawater willbecome progressively enriched in isotopically heavyH2O.
The oxygen isotopic ratio in carbonate shellsis in equilibrium with that in seawater at the time that the shellsform. Therefore, layer by layer study of the oxygen isotopic ratio inshells in marine sedimentary strata can yield a record of the waxingand waning of continental ice sheets. More oxygen 18 means more iceon the continents. More oxygen 16 means less ice.
There are two stable carbon isotopes, carbon 12(6 protons and 6 neutrons) and carbon 13 (6 protons and 7 neutrons).Photosynthetic organisms use disproportionately moreCO2containing the lighter carbon 12 than the heavier carbon 13 (thelighter molecules move faster and therefore diffuse more easily intoplant cells where photosynthesis takes place).
During periods of high biological productivitymore light carbon 12 is locked up in living organisms and organicmatter being buried and preserved in sedimentary rocks. Consequently,the atmosphere and oceans become depleted in carbon 12 and enrichedin carbon 13.
Oxygen Neutrons Electrons
The carbon isotopic ratio in calcareous shellsof marine organisms is in equilibrium with that of seawater. So asmore carbon 12 is held in biomass during times of high primaryproductivity, and increased burial of organic carbon, calcareous(CaCO3)skeletal materials become enriched in carbon 13. During periods oflow biological productivity and decreased burial of organic carbon,for example following mass extinctions, marine calcareous skeletalmaterials become enriched in carbon 12.
Oxygen Neutrons Protons Electrons
Neutrons Oxygen-18 Atom
What Is Oxygen Neutrons
As air cools by rising into the atmosphere or moving toward the poles, moisture begins to condense and fall as precipitation. At first, the rain contains a higher ratio of water made of heavy oxygen, since those molecules condense more easily than water vapor containing light oxygen. The remaining moisture in the air becomes depleted of heavy oxygen as the air continues to move poleward into colder regions. As the moisture reaches the upper latitudes, the falling rain or snow is made up of more and more water molecules containing light oxygen.
Ocean waters rich in heavy oxygen: During ice ages, cooler temperatures extend toward the equator, so the water vapor containing heavy oxygen rains out of the atmosphere at even lower latitudes than it does under milder conditions. The water vapor containing light oxygen moves toward the poles, eventually condenses, and falls onto the ice sheets where it stays. The water remaining in the ocean develops increasingly higher concentration of heavy oxygen compared to the universal standard, and the ice develops a higher concentration of light oxygen. Thus, high concentrations of heavy oxygen in the ocean tell scientists that light oxygen was trapped in the ice sheets. The exact oxygen ratios can show how much ice covered the Earth.
Ocean waters rich in light oxygen: Conversely, as temperatures rise, ice sheets melt, and freshwater runs into the ocean. Melting returns light oxygen to the water, and reduces the salinity of the oceans worldwide. Higher-than-standard global concentrations of light oxygen in ocean water indicate that global temperatures have warmed, resulting in less global ice cover and less saline waters. Because water vapor containing heavy oxygen condenses and falls as rain before water vapor containing light oxygen, higher-than-standard local concentrations of light oxygen indicate that the watersheds draining into the sea in that region experienced heavy rains, producing more diluted waters. Thus, scientists associate lower levels of heavy oxygen (again, compared to the standard) with fresher water, which on a global scale indicates warmer temperatures and melting, and on a local scale indicates heavier rainfall.