Questions about Quantum state, Pauli exclusion principle and chemistry.

[PrincePhoenix]

According to this website,
http://www.particleadventure.org/pauli.html
"At one time, physicists thought that no two particles in the same quantum state could exist in the same place at the same time. This is called the Pauli Exclusion Principle, and it explains why there is chemistry."
1-What does the "particles in the same quantum state" mean? Does it mean particles for which all four quantum numbers are the same or something else?
2-How does it explain there is chemistry?

[MikeyW]

1- yes, pretty much
2- if all particles could occupy the same state, (ie. in the chemistry example if electrons were not fermions) they would all occupy the ground state, and never leave. the forcing of electrons into outer orbitals makes it energetically favourably for some electrons to jump into orbitals of nearby atoms to form ionic bonds, and so on...

[PrincePhoenix]

Thanks. That made it clear for me.