Suns fusing hydrogen...
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Hydrogen isotopes.
Morbo
Sergeant Knight at Arms
They don't fuse into a helium atom in one step. It's something like 2 hydrogen atoms fusing into one deuterium atom, then the deuterium atom with another hydrogen atom into a helium-3 atom, and then...some other step to get to the normal helium(-4).
Can't remember the exact details.
Can't remember the exact details.
G36E
Baron
First read about the Isotopes of Hydrogen.
The hydrogen fusion reactions include the Deuterium-Deuterium, Tritium-Tritium and Deuterium-Tritium reactions:
D-T reaction (lowest threshold energy, ~50 keV)
D + T → He4 (3.5 MeV) + n (14.1 MeV)
D-D reaction (both reactions are equally likely to occur)
D + D → T (1.01 MeV) + p (3.02 MeV)
D + D → T (0.82 MeV) + n (2.45 MeV)
T-T reaction
T + T -> He4 + 2 n (11.3 MeV)
The hydrogen fusion reactions include the Deuterium-Deuterium, Tritium-Tritium and Deuterium-Tritium reactions:
D-T reaction (lowest threshold energy, ~50 keV)
D + T → He4 (3.5 MeV) + n (14.1 MeV)
D-D reaction (both reactions are equally likely to occur)
D + D → T (1.01 MeV) + p (3.02 MeV)
D + D → T (0.82 MeV) + n (2.45 MeV)
T-T reaction
T + T -> He4 + 2 n (11.3 MeV)
TAMULI'S BACK!!!! 
Good to see you back on the forums kid.
Anyway,
Basically what you've got wrong is that fusion doesn't happen between two hydrogen atoms, but between two hydrogen isotope atoms.
As you know the atomic mass of an object is considered to be around it's sum of neutrons and protons, so Hydrogen, which has one proton, and no neutrons, has a mass of around 1. The .0079 comes from the electron. Isotopes however are variants of an atom that contain more neutrons than they normally do. This is how it happens.
There are two Hydrogen atoms,
H+H
They then fuse to create a Deuterium atom, which is a stable isotope of Hydrogen. Basically what happens is that the electron and the proton of the second Hydrogen atom combine to form a Netron, which is then joined to the first Hydrogen atoms nucleus. This means that although Deuterium has the same charge as Hydrogen (One + Proton, one - Electron, and it's neutron which is neutral), it has a higher weight (One proton and one electron, like hydrogen, but also the weight of the neutron, which has the weight of a proton and an electron combined). As such Deuterium has an atomic weight of around 2.014, twice that of hydrogen.
Then, the Deuterium atom fuses with another Hydrogen atom to make an isotope of Helium, called Helium-3, which has two protons, two electrons and a single neutron. The next part is rather more complicated. There are four ways in which Helium is created in the sun, called PP I, PP II and PP III and PP IV.
PP I, which is the most common (86%) fuses two Helium-3's to create a normal helium (Two protons, Two electrons and two neutrons, with an atomic weight of four) and a hydrogen atom.
PP II, occurs 14% of the time and is WAY more complicated.
Basically a Helium-3 and a normal helium (Helium-4) fuse to Beryllium-7, which then combines with a free electron to create Lithium-7, which then combines with a hydrogen to make two helium atoms.
PP III, only happens 0.11% of the time and is even more confusing and complicated than that.
Basically the same as PP II except the Beryllium seven combines with a Hydrogen atom instead of a free electron to form Boron-8, which is unstable and eventually loses an electron, then splits to create two Helium's.
PP IV, is incredibly rare (0.3 parts per million).
Basically the Helium-3 just nabs the proton from a normal hydrogen and makes a helium.
So, uh, long story short, the answer is because it takes more than two hydrogens to make a helium.
Good to see you back on the forums kid.
Anyway,
Basically what you've got wrong is that fusion doesn't happen between two hydrogen atoms, but between two hydrogen isotope atoms.
As you know the atomic mass of an object is considered to be around it's sum of neutrons and protons, so Hydrogen, which has one proton, and no neutrons, has a mass of around 1. The .0079 comes from the electron. Isotopes however are variants of an atom that contain more neutrons than they normally do. This is how it happens.
There are two Hydrogen atoms,
H+H
They then fuse to create a Deuterium atom, which is a stable isotope of Hydrogen. Basically what happens is that the electron and the proton of the second Hydrogen atom combine to form a Netron, which is then joined to the first Hydrogen atoms nucleus. This means that although Deuterium has the same charge as Hydrogen (One + Proton, one - Electron, and it's neutron which is neutral), it has a higher weight (One proton and one electron, like hydrogen, but also the weight of the neutron, which has the weight of a proton and an electron combined). As such Deuterium has an atomic weight of around 2.014, twice that of hydrogen.
Then, the Deuterium atom fuses with another Hydrogen atom to make an isotope of Helium, called Helium-3, which has two protons, two electrons and a single neutron. The next part is rather more complicated. There are four ways in which Helium is created in the sun, called PP I, PP II and PP III and PP IV.
PP I, which is the most common (86%) fuses two Helium-3's to create a normal helium (Two protons, Two electrons and two neutrons, with an atomic weight of four) and a hydrogen atom.
PP II, occurs 14% of the time and is WAY more complicated.
Basically a Helium-3 and a normal helium (Helium-4) fuse to Beryllium-7, which then combines with a free electron to create Lithium-7, which then combines with a hydrogen to make two helium atoms.
PP III, only happens 0.11% of the time and is even more confusing and complicated than that.
Basically the same as PP II except the Beryllium seven combines with a Hydrogen atom instead of a free electron to form Boron-8, which is unstable and eventually loses an electron, then splits to create two Helium's.
PP IV, is incredibly rare (0.3 parts per million).
Basically the Helium-3 just nabs the proton from a normal hydrogen and makes a helium.
So, uh, long story short, the answer is because it takes more than two hydrogens to make a helium.
