Outer Shell - GCSE Chemistry Definition

In GCSE Chemistry, the outer shell is the outermost energy level that contains electrons in an atom. Electrons are arranged in shells (or energy levels) around the nucleus. The number of electrons in the outer shell plays a key role in determining how an atom reacts.

• Atoms with full outer shells (like the noble gases) are stable and unreactive.

• Atoms with only a few electrons in their outer shell (like Group 1 metals) tend to lose them in reactions.

• Atoms with nearly full outer shells (like Group 7 elements) often gain electrons.

Understanding the outer shell helps explain why elements form ionic or covalent bonds and how they behave in chemical reactions.