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Astronomers consider all elements heavier than helium to be metals. That definition
obviously does not jive with the standard chemical definition of a metal as an element
that readily conducts electricity, but a concept called "metallicity"
argues that from a star (and therefore the universe) formation perspective, extremely
high temperatures and pressures in first generation stars (like our sun) preclude
the identification of distinct elements other than hydrogen and helium. Heavier
elements, such as lithium (#3 on the
periodic chart and a major component in LiIon
batteries, is classified as a metal in chemistry) are overwhelmingly created
after a massive enough hydrogen star collapses and begins fusing H and He into heavier
elements. The
relative abundance of hydrogen
in the universe is deemed to be about 92%, and helium is 7.1%, so together they
comprise about 99% of all elements. Universally, oxygen is at 0.1%, carbon is
0.06%, nitrogen is 0.015%, silicon is 0.006%, and iron is 0.004%. By comparison,
the Earth's elemental composition is 48.8% oxygen, 14.3% iron, 13.8% silicon,
0.2% hydrogen, 0.02% carbon, 0.004% nitrogen, and <0.001% helium (which explains
why He was first discovered in a spectrograph of the sun, which is 6% helium).
Periodic Table of Elements showing how they are created.
(origin unknown)
As a point of interest, iron (Fe, #28) is the heaviest element that can be
fused in a star and give off more energy than it takes to cause the fusion.
Heavier elements require a net input of energy to fuse. How, then, are the
heavier elements created if everything began with hydrogen? The violent
gravitational collapse of a heavy star, known as a
supernova, provides that
needed energy, which subsequently causes a proportionally violent explosion
spewing the newly created elements into the universe. The chart to the right
shows by which process(es) the various elements are created.
Posted May 12, 2022
(updated from original post on 4/7/2016)
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