The initial Big Bang explosion is said to have produced hydrogen and helium, which, through later explosions, changed into the heavier elements. But the atomic gaps would forbid this from occurring. 1
"In the sequence of atomic weight, numbers 5 and 8 are vacant. That is, there is no stable atom of mass 5 or mass 8 . . The question then is: How can the build-up of elements by neutron capture get by these gaps? The process could not go beyond helium 4 and even if it spanned this gap it would be stopped again at mass 8 . . This basic objection to Gamow's theory is a great disappointment in view of the promise and philosophical attractiveness of the idea."
—*William A. Fowler, quoted in Creation Science, p. 90 [California Institute of Technology].
"There is no accepted theory as to how the hot gas clouds of hydrogen and helium arising out of the big bang condensed into galaxies, stars and planets. It would seem that the possibility of such a condensation is similar to the probability for all of the air in a room to collect in one corner—just by random motion of the molecules."
—H.M. Morris, W.W. Boardman, and R. F. Koontz, Science and Creation (1971), p. 89.
Alpher–Bethe–Gamow paper - Main shortcoming of the theory
No element was found to have a stable isotope with an atomic mass of five or eight. Physicists soon noticed that these mass gaps would hinder the production of elements beyond helium. Just as it's impossible to climb a staircase one step at a time when one of the steps is missing, this discovery meant that the successive capture theory could not account for higher elements. 2