Predict the ion formed by each element: Part A Rb Express your answer as an ion.

Question

Predict the ion formed by each element:

Part A

Rb

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Part B

K

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Part C

Al

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Part D

O

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Predict the ion formed by each element:

Part A

Rb

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Part B

K

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Part C

Al

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Part D

O

Express your answer as an ion.

Explanation / Answer

Rubidium is an alkali metal with the valence electronic configuration [Kr] 5s1. Thus the most probable ion it forms will be to satisfy the octet rule and attain the configuration of the nearest noble gas which here is krypton. To achieve that, Rb loses its single 5s electron and becomes a stable Rb+ cation.

Potassium is also an alkali metal with the valence electronic configuration [Ar] 4s1. Being in the same group as Rb it too attains the nearest noble gas argon's configuration by ejecting its lone s electron to be K+.

Aluminium has a valence electronic configuration of [Ne] 3s2 3p1. To attain a noble gas configuration, it can either lose three electrons and become Al3+ with Ne configuration or acquire 5 electrons and stay as Al5- which tends to destabilize the nucleus due to its small size and higher nuclear charge. Therefore, Al exists predominantly as Al3+.

Oxygen has an electronic configuration of [Ne] 3s2 3p4. To attain the nearest noble gas configuration, its small size and high electronegativity combined with the negative electron-gain enthalpy makes it favourable for the atom to acquire electrons rather than lose them. This is why oxygen cations are unstable and tend to decompose by rearrangement in reactions while formation of oxygen anion is highly favoured. Thus it can be concluded that O resides predominantly as O2- while other configurations as peroxide (O-) and superoxide (O2-) are also known.

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