is Li ion less stable than Li atom?

Question

so our teacher introduced the concept of ionization energy... heres my doubt : if we remove an electron from , say, Lithium , we need to supply energy first and that will be very less compared to the energy we'll have to supply to , say, oxygen. now the Li ion will have more energy than the lithium atom. but doesnt more enegry = less stability? does that mean Li ion is less stable?

what i really want to ask is, when we remove an electron from an atom, does the atom ' gain' energy or is the gain actually the energy supplied to the electron?

Answer 1

What do you mean by "stable"? In a vacuum, $\ce{Li+}$ is quite stable. In water, Li ionizes readily to $\ce{Li+}$, with $\ce{OH-}$ accepting that electron. Of course, in vacuo, if an $\ce{Li+}$ ion were to be placed near an $\ce{Li-}$ ion, they'd quickly redistribute the charge.

There is also a difference between chemical (thermodynamic) stability and kinetic stability. Lifting a ball up a hill, or lifting an electron to a higher level, gives it potential energy, but if the ball rests in a cup on the hill, or the electron is in a metastable state, it will not go back on its own without a push.

Thermoluminescence is a case in point. Over time, some materials such as ceramics absorb radiation from cosmic sources and nearby radioactive minerals, putting atoms into excited states. Upon reheating, electrons hop back to lower states, emitting light. This is used to date ancient pottery, since the metastable states are preserved for millenia.

Another example of metastability is diamond. It takes considerable pressure and a specific temperature range to convert carbon, e.g. graphite, to diamond -- but once that pressure is removed, graphite is the preferred state. However, once formed, diamond is stable at room temperature for eons.

See Difference between thermodynamic and kinetic stability, answered by thomij, for a much more complete answer.

Answer 2

Actually, this question about the difference in stabilities of the metal atom and the metal ion was discussed in my chemistry class before and I think the idea is not difficult to understand.

If we were to look at the $\ce {Li}$ atom and the $\ce{Li+}$ ion (and electron) in isolation (i.e. ignoring all the interactions with surrounding chemical species, then we can most definitely say that the $\ce {Li+}$ ion (and electron) is higher in energy and thus less thermodynamically stable than the neutral $\ce {Li}$ atom (and electron). This is simply because energy was invested in the ionisation of the $\ce {Li}$ atom so clearly the products of this ionisation, which us an endothermic process, must be higher in energy than the reactant (i.e. the $\ce {Li}$ atom).

However, in reality, things do not occur in isolation in most cases. For example, we lithium is reacted with water in a redox reaction. We see that the more thermodynamically unstable $\ce {Li+}$ ion quickly interacts via ion-dipole interactions with neighbouring water molecules. These interactions are exothermic and bring down the energy of the system drastically. Now, if we consider the lithium ion in this chemical environment versus the unreacted lithium atom, we can clearly conclude that the lithium ion, in its chemical environment with all the coordinating water molecules, must be lower in energy than the latter.

I hope I managed to clarify things for you.

Answer 3

We certainly have to supply energy to an atom to ionise it. Removing an electron from outermost shell of an atom requires energy known as ionization energy. Although, since Li is a metal, the value of its ionization energy is low. Also Li atom is more stable than Li+. However, in aqueous medium, due to extremely large hydration energy (energy evolved when a substance is hydrolysed), in aqueous medium, Li+ is more stable.