Properties of Liquids

Reminder: Kinetic-molecular Theory says the particles of matter are always in motion I.Properties of Liquids & the Kinetic-Molecular Theory A.Compared to Gases: 1.Particles in liquids are closer together 2.Attractive forces between liquid particles are more effective (polarity & hydrogen bonds) 3.Particles are not bound together in fixed positions 4.Fluid: substance that flows and takes shape of its container

Gas ParticlesLiquid Particles

B.Other Properties of Liquids 1.Relatively high density (much more dense than gases as particles are closer together) 2.Relative Incompressibility – liquids are much les compressible than gases (again, particles are closer together) 3.Diffusion – any liquid gradually diffuses throughout any other liquid in which it can dissolve Constant, random motion causes diffusion Slower in liquids than gases, particles are closer together

B.Other Properties of Liquids 4.Surface Tension – force that tends to pull adjacent parts of a liquids surface together, thereby decreasing surface area to the smallest possible size Capillary Action: surface of liquid is attracted to the surface of a solid Allows liquids to travel through narrow tubes, even against gravity!

Surface Tension

B.Other Properties of Liquids 5.Evaporation & Boiling Vaporization: process of a liquid or solid changing to a gas Evaporation: process by which particles escape from the surface of a nonboiling liquid and enter the gas state Boiling: the change of a liquid to bubbles of vapor that appear throughout the liquid 6.Formation of Solids – the physical change of a liquid to a solid by removal of heat energy is freezing

Properties of Solids

I.Properties of Solids & the Kinetic-Molecular Theory A.Intermolecular Forces 1.Much more effective in solids 2.Keeps particles very close together 3.Holds particles in a relatively fixed position, with only vibrational movement around fixed points. 4.For all these reasons, solids are more ordered than liquids, and much more ordered than gases.

B.Two Types of Solids 1.Crystalline Solids – consist of crystals, a substance in which the particles are arranged in an orderly, geometric, repeating pattern 2.Amorphous Solid – particles are arranged randomly (glass & plastics)

B.Other Properties of Solids 1.Definite Shape and Volume Maintain shape without a container Crystalline solids are geometrically regular Amorphous solids have no distinct geometric shapes (glass can be molded) Volume changes only slightly with temperature/pressure changes

2.Definite Melting Point Melting: physical change of a solid to a liquid by adding heat energy Melting Point: temperature at which a solid becomes a liquid; kinetic energies of the particles overcome the attractive forces holding them together Amorphous solids do not have definite melting points, can flow over a range of temperatures Amorphous solids are classified as supercooled liquids, which retain certain liquid properties but appear to be solid

3.High Density & Incompressibility Generally, substances are most dense in the solid state Solids are slightly more dense than liquids and much denser than gases. Solids are not compressible All is due to the particles of solids being closely packed together 4.Low Rate of Diffusion Rate of diffusion is millions of times slower in solids than in liquids

II.Crystalline Solids A.Ionic Crystals - made of positive & negative ions 1.Hard, brittle, high melting points, good insulators B.Covalent Network Crystals - atoms are covalently bonded to their neighbors 1.Hard, brittle, high melting points, nonconductors or semiconductors

C.Metallic Crystals - made of metallic cations surrounded by electrons 1.High electric conductivity D.Covalent Molecular Crystals - molecules are held together by intermolecular forces 1.Soft, low melting points, easily vaporized, good insulators