Reactivity is a measure of how easily an element will combine with other elements to form compounds. Some elements are unreactive and need energy putting in others will react spontaneously and easily.
The size of the nucleus determines the chemical reactivity of the element due to its ability to hold onto electrons and attract electrons. Patterns of reactivity vary depending on the size of the nucleus, the number of electrons and the number of shells. Non metals prefer to attract electrons and metals prefer to lose electrons in general.
Elements are atoms with the same number of protons in the nucleus
How an element or compound will easily gain or lose electrons when interacting with other elements. Reactivity can also be a measure of how violent a reaction is giving our heat or light.
The nucleus is the term given to the centre of the atom comprising of the proton and neutron