States of matter

The three states of matter — solid, liquid, and gas — differ in the arrangement, movement, and energy of their particles.

Solids

• Have their particles in a regular, fixed arrangement, held closely together by strong forces of attraction
• Have particles that vibrate in place about fixed positions
• Have the least energy of the three states

Liquids

• Have particles that are close together but irregularly (randomly) arranged
• Have particles that can move and slide over one another
• Have moderate energy, more than in a solid but less than in a gas

Gases

• Have particles that are far apart, with negligible forces of attraction between them
• Have particles that move rapidly and randomly
• Have the highest kinetic energy of the three states

Interconversions between states occur through heating or cooling: melting, boiling, condensing, freezing, and sublimation each involve characteristic changes in the arrangement, movement, and energy of the particles.

Diffusion

Diffusion provides key evidence for the particle theory, as particles spread from regions of higher concentration to regions of lower concentration through their random motion. Diffusion is faster in gases than in liquids because gas particles move more quickly.

Dissolving

Dissolving involves a solute dispersing throughout a solvent to form a solution.

Key Definition A saturated solution is one that contains the maximum amount of dissolved solute at a given temperature.

Solubility

• Is measured in grams of solute per 100 g of solvent (usually water)
• Typically increases with temperature for solids

Solubility curves display this relationship graphically, allowing the solubility to be read off at any temperature and enabling calculation of the mass of crystals formed when a saturated solution is cooled.

The practical investigation of solubility requires careful temperature control and accurate measurement of the mass of solute that dissolves in a known mass of water.

At a Glance