What is the most abundant chemical element in the universe

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Abundance of the elements

Today we know about the abundance of chemical elements in the Universe, this value measures the abundance or scarcity of the elements.
Abundance is a mass ratio or a ratio of molecules present in a given environment relative to other elements. Most abundances expressed are the mass ratios. For example, the abundance of oxygen mass in water is about 89%, which is the fraction of the mass of water which is composed of oxygen. In the observable universe, the mass abundance of hydrogen is 74%. Analyses of the sky by the WMAP satellite, indicate that the universe is old 13.82 billion years (with an accuracy of 1%), it is composed of 73% dark energy, 23% cold dark matter, and only 4% atoms (chemical elements). The elements are the usual baryonic matter, made of protons, neutrons and electrons, though sometimes in some regions of the Universe such as neutron stars, the matter is in the form of ions.
In the right image, hydrogen is the most abundant element in the universe, followed by helium, oxygen, carbon, neon, nitrogen, magnesium,...
The abundance of hydrogen and helium, i.e. the lightest elementwith an atomic number 1 and 2, dominates the other elements that are rare compared to them. These two elements were produced shortly after the Big Bang, during the primordial nucleosynthesis. All other elements, heavier, were produced much later, in the stars for stellar nucleosynthesis. Although hydrogen and helium make up respectively ≈ 92 and ≈ 7% of the baryonic matter in the universe, the other elements i.e. the remaining 1% is huge masses that have led to the emergence life.
The abundance of elements decreases exponentially with the atomic number (Z). Lithium, Beryllium, Boron are exceptions that show depletion despite their low atomic number. There is a pronounced peak in abundance in the vicinity of iron (Fe). Peer Z are more abundant than their odd neighbors, this is what occurs on the curve, this effect sawtooth (odd-even effect).

nota: Our body is composed of 99% CHON (Hydrogen, Oxygen, Nitrogen and Carbon).

Image: tables of relative abundance of chemical elements in the Universe, Sun and Earth,% are approximate.

Image: Relative abundance of chemical elements in the Universe, based on digital data AGW Cameron: Abundances of elements in the solar system. Z is the atomic number of the element. Abundance of elements decreases exponentially with the atomic number (Z). Lithium, Beryllium, Boron are exceptions that show depletion despite their low atomic number. There is a pronounced peak in abundance in the vicinity of iron (Fe). The even Z are more abundant than their neighboring odd. Credit public domain.

Primitive solar nebula

In the primitive solar nebula, hydrogen (H) and helium (He) is 99.8% by number of the total of the elements present. In the remaining 0.2%, there is in the order after H and He, oxygen, carbon, neon, nitrogen, silicon, magnesium, sulfur, argon, iron, sodium, chlorine, aluminum, calcium,...
When the original cloud rotating has cooled, the elements began to condense. The transition from one state of matter to another is called change of state. When the matter condenses, it changes state, it goes directly from a solid to a gaseous state without passing through the liquid state, is what is known in thermodynamics, condensation. This change is due to a modification of the volume, temperature and / or pressure. Thus, near the center there are refractory materials, those who have good resistance to heat, such as metals and rocks. Further, we will find the volatile materials such as water ice (H2O). Further, there will be molecules of carbon dioxide (CO2), methane (CH4), dinitrogen (N2) and ices. Thus, the telluric planets and gaseous "with a solid core" form close to the star. Those who have a very massive heart (two to four times the mass of Earth) retained the original gas in the nebula, which are gaseous giants. Small planets, not massive enough retained only little gas.

Image: Decreasing abundance (of warmer to cooler), chemical elements in the proto-solar nebula, which is condensed, there are 4.5 billion years.