| How did the elements came to existence?|
|Question Date: 2013-05-30|
Hydrogen was the first element on the periodic
table to form in the universe. After the formation
of hydrogen, all of the other elements formed in
stars via fusion of lower elements. Hydrogen,
having the lowest atomic mass (1 proton and 1
electron) can undergo a fusion reaction with
another hydrogen to form helium (2 protons and 2
electrons). Likewise, other higher elements form
from the fusion of two lower elements. This fusion
process requires a great amount of activation
energy because normally two elements will repel
each other until you overcome this energy barrier
and fuse the two nuclei. This large activation
energy is why the process occurs in stars. Stars
are very massive and the gravitational forces in
the star collapse the mass in the
center--compacting it and making the center very
dense. This forces the nuclei together to cause
fusion. In the end, this fusion process is highly
exothermic (releases a lot of energy) because some
of the rest mass of the two nuclei is converted
into energy through Einstein´s famous E =
mc2 equation. This release of energy is
why stars are hot and emit light.
Hydrogen, helium, and a little bit of lithium
were formed by collisions of elementary particles
in the big bang.
All other elements are made in stars. Elements
up to and including iron can be created by nuclear
fusion, but heavier elements require the violence
of a supernova in order to make them. All heavy
elements (heavier than helium) require supernovae
to distribute them, though, otherwise they just
form cores of white dwarf stars and sit there.
Elements up through iron were formed from
nuclear fusion in stars. Brand new stars that are
not derived from supernovas and other stars dying
originally start with hydrogen. The hydrogen at
their cores undergoes nuclear fusion, turning into
helium and releasing energy in the process. The
remaining hydrogen will continue to undergo
nuclear fusion, as will the helium, and this
process will continue until heavier elements up to
iron. Iron will not undergo fusion in these
conditions because it requires energy rather than
releases energy. Eventually, after the star's
"final" growing stage when it produces iron, the
star's core will begin to collapse rather than
grow. In some cases, a star will experience a
supernova, releasing a huge amount of energy. If
this happens, there is so much energy around that
fusion of iron and heavier elements is possible.
This is where heavier elements will come from.
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