Liquid State – Structural Model for Liquid

8/3/2019 Liquid State – Structural Model for Liquid

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James Le AP Chemistry – Ms.Gawle Gawlik

11/09/2011



Overview Liquid, one of the three physical states in which matter

can exist.

The other two states are solid and gaseous. Liquids and gases take the shape of their container,

unlike solids, which keep their own shape.

Liquids and solids maintain a definite volume, or size,

while gases will expand to fill a container. Liquids, particularly water, are essential to life.

Besides, they are also important in everyday activities.



Structural Model for Liquids Liquids, like all substances, are made up of atoms or

bonded groups of atoms called molecules

The physical state of any substance— whether the

substance is a liquid, solid, or gas—depends on thearrangement of the molecules in the substance

The molecules in a liquid are arranged tighter and moreorderly than in a gas, but less orderly than in a solid

Liquids have short-range order, or an orderly pattern only at very small distances (a few molecule lengths) from agiven molecule

Certain liquids, called liquid crystals, can have some long-range order, thought not as much as a solid



Structural Model for Liquids Order in the molecules of any substance depends on

the forces of attraction and repulsion between themolecules – intermolecular forces

Intermolecular forces arise from electrical charges onmolecules that attract or repel the charges on othermolecules

Intermolecular forces account for many of the physical

properties of a liquid, such as its boiling point,freezing point, and surface tension

They are also the reason a liquid can form from a gas orfreeze into a solid



Physical Properties Boiling Point: The boiling point of a liquid is the

temperature at which molecules escape from the liquid andenter the gaseous state

At the boiling point, the vapor pressure of a liquid mustequal the pressure of the atmosphere above the liquid

The boiling point of a liquid is lower at higher elevationsbecause atmospheric pressure decreases as altitude

Different materials have different boiling points becausethe forces of attraction between their molecules differ



Physical Properties Freezing point: The freezing point of a substance is the

temperature at which the liquid form of the substancebecomes a solid

The freezing point of a substance is essentially the same asits melting point—that is, the point at which a solidbecomes a liquid

The viscosity of a liquid is a measure of how much theliquid resists flow

A liquid’s viscosity depends on the structure of the liquid’smolecules and on the attractive forces between the liquid’smolecules

Liquids with large intermolecular forces tend to be highly viscous



Physical Properties To increase a liquid’s surface area, molecules must

move from the interior of the liquid to the surface

Requires energy (some intermolecular forces must beovercome)

The resistance of a liquid to an increase in its surfacearea is called the surface tension

Liquids with large intermolecular forces tend to havehigh surface tensions



Physical Properties Polar liquids exhibit capillary action, the

spontaneous rising of a liquid in a narrow tube

Capillary action occurs when the attraction of aliquid’s molecules for themselves differs from theirattraction for a solid that the liquid contacts

Two different types of forces are responsible for this

property: cohesive forces, the intermolecular forcesamong the molecules of the liquid, and adhesive forces, the forces between the liquid molecules andtheir container

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Liquid State – Structural Model for Liquid