The Nature of Liquids and Solids

States of Matter Plasma - typically an ionized gas. “Ionized" refers to presence of one or more free electrons. The free electrons make the plasma respond strongly to electromagnetic fields. GAS – form of matter that has no definite shape or volume; it adopts the shape and volume of it’s container. Liquid – form of matter that flows, has a fixed volume, and takes the shape of it’s container. Solid – matter that has a definite shape and volume.

Activities Two different activities per table For Each Water temperature versus boiling point Water density at and near freezing For Each Hypothesis Experimental Plan/Experiment Data Interpretations Conclusion Regarding Hypothesis Supported Not Supported Contradicted

Liquids The particles that make up a liquid are in motion just like those in a gas Liquid particles are attracted to each other, unlike gas particles O2 as a molecule is linear and non-polar H2O as a molecule is bent tri-atomic and polar Particles are still free to flow past each other

Kinetic Theory The intermolecular forces of liquids contribute to the average kinetic energy of the particles Most particles still do not have enough kinetic energy to escape into the gaseous state The intermolecular forces also force the liquid molecules closer together, causing liquids to have a higher density than gases

Evaporation The conversion of a liquid to a gas or a vapor is defined as vaporization When such a conversion occurs at the surface of a liquid that is not boiling, the process is defined as evaporation Only molecules with enough kinetic energy can break away from the surface of the liquid The hotter the liquid the greater the rate of evaporation Examples Evaporative cooling effect of perspiration Cloth canteen cover

Boiling Point The boiling point is the temperature a twhich the vapor pressure of the liquid is just equal to the external pressure Bubbles of vapor form throughout the liquid, starting at the surface nearest the heat source, rise to the surface and escape into the air. The average kinetic energy is the same for the liquid and the vapor, same temperature, but the potential of the steam is much higher – can do more work or cause more damage (burns to skin from hot liquid vs. vapor)

Normal Boiling Point Then normal boiling point is defined as the boiling point of a liquid at a pressure of 101.3 kPa. Using other units – one atmosphere, 760 mm Hg, 14.7 psi The normal boiling point of water is 100oC Devices that take advantage of the relationship between boiling temperature and surrounding pressure Pressure cookers Autoclaves – used to sterilize medical instruments Steam boilers

Example of Super-Heated Steam Boiler

Determining Normal Boiling Points for Several Substances Vapor Pressures (kPa) of Several Substances at Various Temperatures OoC 20oC 40oC 60oC 80oC 100oC Water 0.61 2.33 7.37 19.92 47.34 101.33 Ethanol 1.63 5.85 18.04 47.02 108.34 225.75 Diethyl Ether 24.70 58.96 122.80 230.65 399.11 647.87 p. 276 in text

Sample Problem – Figure 10.11 V A P O R E S U k a Temperature (deg C)

Solids In most solids the particles are packed against each other in a highly organized manner Particles do not flow/take on container shape Particles vibrate about fixed points

Discussion What else, besides a temperature change, will cause gas pressure to increase?

Melting Point The temperature at which the solid turns into a liquid Vibrations of molecules are able to overcome the forces that hold them in fixed positions In general, ionic solids or those that have greater polarity have higher melting points

Crystal Structure and Unit Cells Atoms, ions, or molecules that make up the solid substance are arranged in an orderly, repeating, three dimensional pattern. The smallest group of particles that retains the geometric shape of the crystal is known as the unit cell See page 281

Cubic Unit Cell Examples

Solids of More Than One Form - Allotropes

Amorphous Solids Some lack an ordered internal structure Rubber, plastic, and asphalt Some have cooled to a rigid state without crystallizing Glass, does not melt at a definite temperature but gradually softens when heated

Amorphous Solids Some lack an ordered internal structure Rubber, plastic, and asphalt Some have cooled to a rigid state without crystallizing Glass, does not melt at a definite temperature but gradually softens when heated