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Some Physical Propertiesof

Matter

Property Comment

ColorState ofmatter Is it a solid, liquid, or gas?

Melting point The temperature at which a solid melts

Boiling point The temperature at which a liquid boils

Heat ofvaporization The heat required to change a liquid to a vapor

Heat offusion The heat required to change a solid to a liquid

Density Usually expressed in units ofgrams per milliliter

or grams per cubic centimeter

Solubility The amount ofa substance that can dissolve in a

given mass or volume ofwater or other solvent

Metallic character Hardness, solidity

Electrical conductivity

Conductivity ofheat

Magnetic properties

Shape ofthe crystals ofa solid

Malleability

Ductility

Viscosity

The ease with which a solid can be deformed

The ease with which a solid can be drawn into

a Wire

The susceptibility ofa liquid to flow

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A solid can be recognized because it has a rigid shape and a fixed

volume that changes very little as temperature and pressure change.

Like a solid, a liquid has a fixed volume, but a liquid is fluid-it

takes on the shape ofits container and has no definite form ofits own.

Gases are fluid also, but gases expand to fill whatever container they

occupy, and their volume varies considerably with temperature and

pressure.

For most substances, the volume ofthe solid is slightly less than the

volume ofthe same mass ofliquid, but the volume ofthe same mass ofgas is much, much larger.

Virtually all matter is found in the solid state at very low temperatures.

As the temperature is raised, though, solids generally melt to form

liquids. Eventually, ifthe temperature is raised high enough, liquids can

evaporate to form gases.*

All the physical properties just described can be observed by the

unaided human senses and refer to samples ofmatter large enough to

be seen, measured, and handled. Such samples are called macroscopic,

in contrast to microscopic samples, such as biological cells and

microorganisms, which are so small that they can only be seen with a

microscope. The structure ofmatter that really interests chemists,

however, is at the submicroscopic scale ofatoms and molecules.

A fundamental idea ofchemistry is that matter exists as it does

because ofthe nature ofits parts, and those parts are very, very tiny .

Therefore, imagination is required to discover useful ideas thatconnect the behavior ofthose tiny parts to the behavior ofchemical

substances in the macroscopic world.

*A fourth state ofmatter, plasmas, are gases composed ofcharged particles.

Plasmas exist naturally in the outer portion ofthe earth's atmosphere, in the

atmosphere ofstars, and in the beautiful aurora borealis or "northern lights. "

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Kinetic-Molecular Theory:

One theory that helps us interpret the physical properties ofsolids,

liquids, and gases is the kinetic-molecular theory ofmatter.

According to this theory, all matter consists ofextremely tiny

particles (atoms and molecules), which are in constant motion.

In a solid these particles are packed closely together in a regular

array (Figure 1.3).

The particle vibrate back and forth about their average pos itions, but

seldom does a particle in a solid squeeze past its immediate neighbors

to come into contact with a new set ofparticles. Because the particles

are packed so tightly and in such a regular arrangement, a solid is

rigid, its volume is fixed.

Gas Liquid Solid

Figure1.3 The three states ofmatter. In the gas phase, atoms or molecules

move rapidly over distances larger than the sizes ofthe atoms or moleculesthemselves. There is little interaction between them. Cooling, increasingthe

pressure, or both, converts gases to liquids. The atoms or molecules are nowmuch closer together, and they interact with one anoth er. Motion ofthe particles

is still very evident, although the particles move over only very small distances,

Further cooling converts a liquid to a solid. The particles are even closer

together and almost totally restricted to specific locations. They are arranged

with a high degree ofregularity.

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Another very useful physical property ofpure elements and compounds

is the temperature at which the solid melts (its melting point) or theliquid boils (its boiling point).

Temperature is the property ofmatter that determines whether heat

(energy) can be transferred from one body to another andthe direction

ofthat transfer: heat energy transfers spontaneously only from a hotter

object to a cooler one.

The number that represents an object's temperature depends on the unit

chosen for the measurement.

Three scales for temperature measurement are in common use today:

Fahrenheit, Celsius, and Kelvin (Figure 1.7).

The Celsius scale is generally used for measurements in the laboratory.

When calculations incorporate temperature data, however, the data

generally must be expressed in kelvins.

Figure 1.7 A comparison ofFahrenheit,

Celsius, and Kelvin temperature

scales. The reference, or starting

point, for the Kelvin scale is

absolute zero (0 K= ~ 2 7 3 . 1 5 C),which has been shown theoretically

to be the lowest possible

temperature. Note that theabbreviation K for the kelvin unit

is used withoutthe degree sign (0).

Also note that I C = I K =(9/5) OF.r\

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