Simplify the following text for a Grade 9 native English-speaking person.
Original: These dimensions are much smaller than the diameter of the atom itself ( nucleus + electronic cloud ) , by a factor of about 23,000 ( uranium ) to about 145,000 ( hydrogen ) .
Simplified: These sizes are much smaller than the size of the atom itself by a factor of about 23,000 ( uranium ) to about 145,000 ( hydrogen ) .