Solids, Liquids, and Gases States of Matter

Solids, Liquids, Gases Solids - Atoms and molecules vibrate in a stationary spot Liquids – atoms and molecules move, but are still bound together Gases – atoms and molecules move freely and bounce off one another without sticking together

Forces that hold matter together Matter is held together by forces of attraction The forces of attraction must be strong enough to overcome the energy of atoms in motion For a substance to go from solid to liquid, or liquid to gas, forces of attraction must be overcome by motion of particles – Higher melting and boiling points mean stronger forces

Forces of attraction Strongest to weakest – Chemical bonds – Hydrogen bonds – Dipole-dipole interactions – London dispersion forces

What makes a substance a solid, liquid, or gas? Strength of bonds Size of the molecule, if molecular Temperature – Metallic substances and ionic substances (and some covalent substances) are bound together in large arrays with strong bonds – solids under normal conditions

Dipole Forces All three types of forces other than bonds are similar – based on electric attraction All are based on dipole moments – a positive end and a negative end of an atom or molecule Hydrogen Bonds are strongest Then permanent dipoles Then temporary dipoles – London dispersion forces

Solids Usually more dense than liquids Often have particles in a particular arrangement – a crystal formation – Crystals may be of many types – Governed by electric forces – could be ions, dipoles, hydrogen bonds Amorphous solids are those without a crystal structure

Liquids In a liquid, molecules, atoms and ions can move freely (fluid), but are still attached to others The ease of flow is called viscosity Most substances flow more easily as the particles get warmer Surface tension is the force at the surface of the liquid

Gases Gases are individual particles in motion, but not attached to others – When they hit another particle, they bounce off The volume of the gas particles is small in relation to the total volume, so gases can be compressed, where solids and liquids cannot

Phase Change When a substance is melted or boils, energy must be supplied When a substance condenses or freezes, energy is released This energy is called – Heat of fusion (for melting and freezing) – Heat of vaporization (for boiling and condensing)

Deposition and sublimation In some conditions a substance may go directly from a vapor state to a solid state, called deposition Going from a solid state to a vapor state is called sublimation Vapor to solid is called deposition

Vapor Pressure Even when below the boiling point, some molecules have enough energy to escape from a liquid These molecules exert a pressure, called the Vapor Pressure