Simplify the following text for a Grade 5 native English-speaking person.
Original: The valence shell is the outermost shell of an atom in its uncombined state , which contains the electrons most likely to account for the nature of any reactions involving the atom and of the bonding interactions it has with other atoms . Care must be taken to note that the outermost shell of an ion is not commonly termed valence shell .
Simplified: The valence shell is the outermost shell of an atom .