I had this doubt since so many years. Suppose you pour water on the floor. Then you switch on the ceiling fan and select stage 5 on its regulator. Then the water on the floor evaporates without reaching its boiling point at 100°C, within a few hours or minutes.
Is the boiling point of water really 100°C, or is that a myth?
The theory involved is Dalton's law of partial pressure and vapor pressure of matter.
Our atmosphere is not a vacuum. It consists of various material, usually the elements and compounds in their gaseous state (there are also solids as dust, etc as pollutants); e.g nitrogen, oxygen, CO₂, water H₂O in the gaseous state. At any temperature there is a pressure (due only to the water vapor) below which water may exists in the gaseous state (this data is found in the so called vapor pressure data for water). Say you have a vessel which is vacuum and the room temperature is 20⁰ C. If you introduce enough water into the vessel, it will evaporate as gaseous vapor until the pressure is about 0.2 atmosphere pressure maximum. This is evaporation. Water in a plate left in the open will evaporate (same as boiling) at say 20⁰ C room temperature as long as the air is not already saturated with water vapor. Water will "boil" (evaporate) at 20⁰ C as long as the contribution of the water vapor to the total pressure of the atmosphere (about 1 atm) is small, say < 0.2 atm.
Water boils at 100⁰ C at 1 atm pressure is correct (water boils at 20⁰ C at about 0.2 atm pressure). This boiling we do in the kitchen kettle is the bubble that forms at the bottom and rises to the surface and breaks. If the temperature is below 100⁰ C, any attempt to form gas bubble would fail as the water pressure is too strong and collapses it. At 100⁰C, the water vapor pressure itself (due solely to gaseous water) reaches also 1 atm and a bubble formed can withstand the pressure of the water trying to collapse it - thus bubbling of "boiling" starts.
The processes of evaporation and boiling are distinct, though they are of course related.
Evaporation essentially describes water dissolving into the air, and it can happen at any temperature. In essence, at any temperature the water molecules have a distribution of energies, with some slower and some faster. If one of the faster molecules reaches the surface, there's a chance that it will be going fast enough to leave the surface.
Evaporation has a converse process, called condensation: the molecules in the air also have a distribution of velocities, and if one of the slower ones hits the surface of a puddle, there's a high chance that it will stick and enter the liquid. In equilibrium, both processes happen at the same rate, with no net evaporation. However, if the air is dry, you'll have a lot less condensation than evaporation and the puddle will dry out.
Boiling describes the point where adding heat to water no longer raises its temperature; instead, all the added energy is spent into sending off the faster molecules into the surrounding air. For water below the boiling point, adding heat will raise the temperature (and make evaporation more likely), but at the boiling point this can no longer happen and all the heat goes into evaporation.
There is a difference between dissolving and boiling.
Imaging that you pick out each water molecule one at a time and throw it into the air. When you have picked them all up like this, there is no more water. The water never reached the boiling temperature, but it still disappeared into the air.
This is what happens. You have probably heard about humidity levels in air, and they tell how much water air can contain as gas. If the max humidity level is not reached (dry air), the air will absorb water molecules, when possible by "picking out one molecule at a time" and freeing it from the liquid water.
When water is boiling, heat is added so that the water molecules are unable to stay together (they move around too "violently" and are ripped apart simply from being too energetic). When water is dissolved in air, it is diffusion because of the concentration difference that is powerful enough to rip molecules free (the air "wants" the water molecules more than the liquid water "is able to hold on to them").
