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==Key Stage 4==
[[File:CsKS4.PNG|right|200px|thumb|The [[Chemical Symbol|chemical symbol]] for [[Caesium]].]]
===Meaning===
[[Caesium]] is a [[Group 1]] [[element]], on the [[Periodic Table]], with 55 [[proton]]s in the [[Atomic Nucleus|nucleus]].
: The most [[Stable Isotope|stable isotope]] of [[Caesium]] has 78 [[neutron]]s in its [[Atomic Nucleus|nucleus]] giving it an [[Relative Atomic Mass|atomic mass]] of 133.
: An [[atom]] of [[Caesium]] has only 1 [[electron]] in its [[Outer Shell|outer shell]].
: [[Caesium]] [[ion]]s have lost an [[electron]] to become [[Positive ChargedCharge|positively charged]].
====Properties====
: [[Caesium]] is a more [[Reactivity|reactive]] [[Alkali Metal|alkali metal]] than [[Rubidium]] but less [[Reactivity|reactive]] than [[Francium]].