you said in ur answer that though atom is small it has infinite energy shells so how they are accommodated in a very very small microscopic atom? plz explain it....it's really confusing me

Energy levels are the shells around the nucleus where electrons are present and and energy levels are imaginary boundary and can be infinite in number around the nucleus and it is not important that electron can present upto infinite energy shell, it depends on element to element.. An atom has not real boundary but the maximum size of an atom is of the order of 10-8 cm.The centrifugal force of attraction provide by positively charged nucleus.