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
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