Definition:

* A boiling point liquid is a liquid at its boiling point, the temperature at which its vapor pressure equals the surrounding atmospheric pressure.

Characteristics:

* Dynamic equilibrium: At the boiling point, the rate of liquid molecules escaping into the gas phase equals the rate of gas molecules returning to the liquid phase. It's a state of balance.

* Constant temperature: The temperature of a boiling liquid remains constant, even though heat is continuously being added. This heat energy is used to overcome the intermolecular forces holding the liquid molecules together.

* Bubbles: Boiling is characterized by the formation of bubbles within the liquid. These bubbles are filled with the vapor of the liquid, and they rise to the surface and escape.

* Energy input: It takes a lot of energy to boil a liquid. The energy needed to convert a liquid to a gas is called the heat of vaporization.

* Vapor pressure: The vapor pressure of a liquid is the pressure exerted by its vapor when it is in equilibrium with the liquid. At the boiling point, the vapor pressure equals the surrounding atmospheric pressure.

Factors affecting boiling point:

* Intermolecular forces: Liquids with stronger intermolecular forces (like hydrogen bonding) have higher boiling points.

* Pressure: Boiling point decreases as pressure decreases. This is why water boils at a lower temperature at higher altitudes where the atmospheric pressure is lower.

* Impurities: The presence of impurities can sometimes affect the boiling point of a liquid, especially if the impurities are dissolved in the liquid.

Examples:

* Water boils at 100°C (212°F) at standard atmospheric pressure.

* Ethanol boils at 78°C (173°F) at standard atmospheric pressure.

In summary: A boiling point liquid is a liquid at its boiling point where the liquid and gas phases are in equilibrium, characterized by constant temperature, bubble formation, and a significant energy input.