Physical properties of a liquid
Liquids are known for flowing and adapting to the shape of their container but they cannot be compressed. This is because liquid particles are held together rather loosely.
The attraction bond between the particles is strong enough to keep the liquid together but weak enough to allow the particles to move around and slide past each other. This is why liquids are in between solids and gas, their particles are not as close together as solids or as far apart as gases.
Although liquids do not have a definite shape they do have a definite volume. No matter what container they are in they always have the same volume. Volume is generally expressed in litres.
Liquids that flow slowly have a high viscosity (thickness). 
Some fluids, like tar, have such a high viscosity that they may seem solid.
Liquids are categorised into pure liquid and mixed liquids. Liquid mixtures like the ocean have other substances dissolved in them such as salt, whereas pure liquids do not.
Changing state
When substances change state their atoms and molecules don't change, but the way they move about does. Water, for example, always has the same number and types of atoms whether it’s in a state of solid, liquid or gas. It is always made up of two hydrogen atoms and one oxygen so it always has the same mass.
Matter changes state when more energy gets added to it. Energy is often added in the form of heat or pressure. When a liquid is heated, its particles begin to move faster. They can move so quickly that they leave the liquid phase and start to move freely like gas particles.
Liquids can change state passing from liquid to solid by freezing and can turn back into liquid by melting. Liquids can turn into steam or gas by evaporating.
Freezing point and boiling point
The freezing and boiling point is the temperature at which a substance freezes or melts and changes state. Each substance has their very own freezing and boiling point.
Water boils at 100ºC, that is its boiling point, it freezes at 0ºC. Acetic acid which is found in vinegar has a boiling point of 117.9ºC and a freezing point of 16.6ºC. Metals are solids at room temperature, all except mercury which is liquid at room temperature. Mercury’s freezing point is -38.87ºC and its boiling point is 365.9ºC. That’s very hot!
