Question

every element in universe is made in stars by fusing lighter elements..right naa? to get to lower binding energy nucleus.
why do elements go on fusing beyond stable nucleus? why/how elements like uranium (radioactive/and unstable nucleus are formed) were formed..

Answer 1

In the first few minutes after the Big Bang, the temperature of the newborn Universe cooled down (to a few billion degrees!) to form hydrogen and helium. Stars spend most of their life burning hydrogen into helium. Only when temperature and pressure become high enough do they start to fuse helium atoms, forming new elements. Lighter elements are the bricks that successively fuse together to produce heavier elements, up to iron-56.
Iron-56 has the most stable nucleus
So, where do heavier elements such as lead, silver, gold and uranium come from? There is no magic: the Universe provides other fascinating ways to produce all the heavy elements. In the high temperature and pressure of a star, fusion is as spontaneous as rolling down a hill (a process that releases energy). However, these new mechanisms are more laborious, like climbing a hill (a process that needs energy). Furthermore the next stages of nucleosynthesis are quite hectic, as they involve captures and explosions. Three types of capture are involved, two dealing with the capture of neutrons (the s- and r-processes) and one with the capture of protons (the p-process).
Neutron capture

One route to create elements heavier than iron-56 starts when extra neutrons collide and fuse with an existing nucleus. In this way we get neutron-richer, heavier nuclei, but with the same number of protons, or the same atomic number. These nuclei are just heavier isotopes of the original element, so we have not yet achieved our aim of creating a heavier, different element.

However, the process has not yet finished. These new isotopes may be stable or unstable, depending on their number of protons and neutrons. If the neutron capture produces an unstable isotope, then it can undergo a spontaneous radioactive decay. One such decay is ‘beta decay’, in which an electron and an anti-neutrino are emitted, so that one of the nucleus’ neutrons is converted into a proton. The net result of this conversion is a nucleus with one more proton and one fewer neutrons. Since the number of protons has changed, this has indeed produced a new, different element.

In this process of neutron capture followed by beta decay, it is important whether the initial neutron capture is slow or rapid relative to the beta decay. The two cases, referred to respectively as the s-process and r-process, produce different elements and occur in different circumstances in the Universe.....................so on i think it is more than enough:)

Answer 2

wow!!!
thanks a lot... i got half of it.. there are a few terms.. like s- process r- process.. etc i will have to google them and learn more..
but seriously... thanks a lot!!!! :) that was really helpful!

Answer 3

for your help i m here:)

Answer 4

fusing atoms higher than iron takes more energy that it releases,
elements above iron are created in super nova, when a tremendous amount of energy is released