Question

(EMG) Which sequence contains elements listed from most reactive to least?

Answer 1

1. Alkali metals, alkaline earth metals, noble gases In general, the reactivity of an element is related to how full it's outer electron shell is. If it's almost empty and only needs to lose 1 electron, it's highly reactive. If it's almost full and only needs to gain 1 electron, it's also highly reactive. If it's completely full and doesn't need to gain or lose an electron, it's practically inert and non-reactive. As it gets closer to being only half full, it tends to be less reactive. With that in mind, let's look at the choices and see if they make sense. 1. Alkali metals, alkaline earth metals, noble gases Alkali metals - First column of periodic table. Only 1 electron in its valance shell. Very reactive. alkaline earth metals - Second column of periodic table, Only 2 electrons in their valiance shells. Still quite reactive, but not as much as the Alkali metals. noble gases - Last column of the periodic table. Valance shell full. Very non-reactive. Overall, this looks like a very good choice. 2. Transition metals, alkali metals, alkaline earth metals Transition metals - Middle of the periodic chart, only average reactivity. alkali metals - As mentioned above, very reactive. Bad choice, going from lower reactivity to higher reactivity. Wrong answer. 3. Alkaline earth metals, alkali metals, halogens Alkaline earth metals - 2 valance electrons. Pretty reactive. alkali metals - 1 valance electron, extremely reactive. Bad choice, going from lower reactivity to higher reactivity. Wrong answer. 4. Transition metals, noble gases, halogen Transition metals - Middle of periodic table, average reactivity. noble gases - Full valance shells, non-reactive. halogen - Missing 1 electron from their valance shells. Highly reactive. Bad choice, medium, low, high. Not a consistent trend from reactive to non-reactive. Wrong answer.