why do alkali metals burst into flames in H2O

[thor3436]

im thinking it has somthing to do with the electron shells and how
theyre arranged but i cant figure that out so im going to google it

[thor3436]

i googled it and it turns out it has somthing to do with
electronegativity [thats a LONG word]

[Paul Robbins]

They burst into flames (some of them do, sodium and lithium don't) because:

1. The reaction with water produces hydrogen which can burn.
2. The energy released by the reaction is released very quickly, which ignites the hydrogen.

The energy release is quick because alkali metals' enthalpy of ionization is lower than any other metals'. This means very little energy is needed for a group 1 metal to lose one electron, so they ionize faster than other metals can, which means the overall reaction if fast, which means the energy is released in a quick burst, which results in a higher temperature - enough to ignite hydrogen - than if it were released more slowly.

[thor3436]

thanks but do you know why they release hydrogen

[Paul Robbins]

Group 1 metal atoms eject an electron if they get the chance, because that's how they can achieve a stable electronic structure. If there's anything around that can accept the electron, the transfer will take place.

When you add a group 1 metal to water, each electron ejected by a metal atom likes to associate with the OH part of H₂O, forming OH^- with an H atom left over. Each H is highly reactive and combines with another H to form H₂.

Chemical Equation

M + H₂O -----> MOH + H₂

MOH is M⁺ OH^- if you want to show the charges.

Word Equation

alkali metal + water -----> alkali metal hydroxide + hydrogen

[thor3436]

well thanks that clears it up alot