Water doesn't turn into steam when heated in a vacuum chamber (no air) because the absence of air or a significant decrease in air pressure lowers the boiling point of water.
Under normal atmospheric pressure (1 atm), water boils at 100 degrees Celsius (212 degrees Fahrenheit). However, as pressure decreases, the boiling point of water also decreases. In a vacuum chamber where the air pressure is significantly reduced, water can boil at much lower temperatures.
At extremely low pressures, such as in outer space where there is almost a complete vacuum, water can boil at temperatures close to its freezing point. The low pressure causes the water molecules to gain enough energy to transition directly from the liquid phase to the gaseous phase without passing through the intermediate phase of steam.
In a vacuum chamber, the lack of air pressure prevents the water from reaching its normal boiling point. Without sufficient pressure to overcome the cohesive forces between water molecules, the liquid water will not convert into steam. However, if the temperature is increased sufficiently, the water will eventually evaporate, but the process would take longer compared to boiling at normal atmospheric pressure.
It's worth noting that even in a vacuum, there may still be some residual air or gas present, which can affect the boiling behavior of water to some extent.