Chemistry

Lecture #7bPhases of Matter

The Phases of Matter

• Solid• Liquid• Gas• Plasma

A solid has definite shape and volume.

Solids have 2 phases: amorphous and crystalline.

Solids are usually hard because their molecules have been packed together. The atoms or molecules of a solid will spin, but not move from their position.

Amorphous solids are solids that have relatively short chains of atoms (tens to hundreds of atoms long). The atom chains move and give the solid the ability to change shape, yet remain solid to the touch. Amorphous solids do not flow.

Crystalline solids are solids that have long chains of atoms (millions of atoms long). The atom chains cannot move, so the solid cannot change shape.

Crystal Lattice

• Appears only in a solid.• Shapes are clearly defined and symmetrical. • Particles are in a 3-D pattern which repeats.

Amorphous Material

• Incomplete crystal lattice• Candles and cotton candy are examples• No defined shape or form

A liquid has definite volume, but takes the shape of the container. Liquids can flow. Liquids are difficult to compress (push the molecules together). The molecules move freely within the bounds of the liquid, though they can escape.

Molecules of a liquid are cohesive, meaning they stick together.

When a solid melts, its crystal lattices disintigrate and particles lose their 3-D pattern. However, when some materials called liquid crystals melt, they lose their

Rigid organization in only one or 2 dimensions. The forces holding the particles together are fairly weak. When the lattices are broken, the crystal can flow like a liquid. Liquid crystal displays (LCDs) are used in watches, thermometer, laptop computers, and calculators because they can melt and solidify with varying electrical charges.

A gas takes the shape and volume of the container. Gases can flow.

The molecules in a gas bounce around, hitting each other and the container they are in. Another word for gas is vapor.

Molecules in solids do not move much and have very little energy.

Liquids move around moderately quickly and have a moderate amount of energy.

Gas molecules move very fast and have a lot of energy.

Solids do not fill their container at all.

Liquids fill the bottom of their container.

Gases fill their container completely.

Plasma is the most common phase of matter in the universe, but the least common found on Earth. Plasmas are gases made of positively and negatively charged atoms and molecules. Examples of plasma include lightening, the gas found in fluorescent light bulbs, the gas found on stars, and the Aurora Borealis (Northern Lights).

Examples of Plasma:

PlasmaMolecules are dissociated into component atoms; electrons move freely among positively charged ions. The plasma state pertains to high energy gas, more relevant to astrophysics than planetary sciences.

SolidAtoms or molecules are held in place, closely packed together; bonds are tight. A solid has a fixed shape and volume.

GasAtoms or molecules move essentially unconstrained. Low density state of matter, having neither fixed volume or shape. A gas will expand to fill the available volume.

LiquidAtoms or molecules remain together, but move relatively easy. A liquid will assume the shape of its container, but has a fixed volume depending upon the temperature.