STATES of MATTER

Matter exists on Earth in the form of solids, liquids, and gases.

The kinetic-molecular theory explains the behavior of these particles. Matter is composed of small particles such as atoms or molecules.

The Nature of Gases

The kinetic-molecular theory of gases states: 1.The particles in a gas are tiny, hard spheres that are far apart. Gases occupy about 1000 times more volume than liquids and solids. These particles are very far apart, as a result, most of the volume occupied by a gas is empty space.

1 unit

Because of the large amount of empty space, gases have low density, about 1/1000 that of a liquid. Gases are very compressible. During compression, the gas particles are squeezed closer together.

2. The particles in a gas are in continuous, rapid, and random motion. The particles travel in straight-line paths until they collide with another particle, or another object, such as the wall of their container. The particles change direction only when they rebound from these collisions. The average speed of oxygen molecules in air at 20 °C is an amazing 1700 km/h!!!

The motion of the particles in a gas allow gases to completely fill any container in which they are enclosed, and they take its shape. Gases do not have a definite shape or a definite volume.

3. Collisions between gas particles are elastic. (and between gas particles and their container). During an elastic collision, kinetic energy is transferred without loss from one particle to another, and the total kinetic energy remains constant.

4. There are no forces of attraction between particles When gas particles collide, they do not stick together but immediately bounce apart.

5. The temperature of a gas depends on the average kinetic energy of the particles of the gas. m = mass v = speed The kinetic energy of any moving object: The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies.

Most of the particles have kinetic energies somewhere in the middle of this range. Therefore, we use average kinetic energy when discussing the kinetic energy of a collection of particles in a substance.

The average kinetic energies and the average speeds of gas particles increase with an increase in temperature and decrease with a decrease in temperature.

Atoms and molecules at higher temperature have greater KE and have a wider range of KE. Also, a much larger number of molecules have large KE. SKIP

You can reasonably expect the particles of all substances to stop moving at some very low temperature. Absolute zero is the temperature at which the motion of particles theoretically seizes. Absolute zero = 0 K or °C

The coldest temperatures recorded naturally are from space. The coldest known region of space called the boomerang nebula has a temperature of 1 K.

When you think of Earth’s oceans, lakes, and rivers and the many liquids you use every day, it is hard to believe that liquids are the least common state of matter in the universe. LIQUIDS

A liquid is a form of matter that has a definite volume and no definite shape, takes the shape of its container. The Nature of Liquids

Particles in a liquid are in constant motion. However, the intermolecular forces between particles pull the particles much closer together than in a gas. A fluid is a substance that can flow and therefore take the shape of its container. Liquids and gases are fluids. The particles in a liquid are able to flow past each other.

Liquids are hundreds of times more dense than gases. This higher density is a result of the close arrangement of its particles. At the same temperature and pressure, different liquids can differ greatly in density.

Liquids are relatively incompressible. When a liquid at 20 °C is compressed by a pressure of 1000 atm, its volume decreases by only 4%.

Cohesion is an attraction between molecules of the same substance…. molecules stick to each other.

A property common to all liquids is surface tension. Surface tension is a force that tends to pull adjacent parts of a liquid’s surface together, and is the result of intermolecular forces. The larger the force of attraction, the larger the surface tension. Water has a very large surface tension. Cohesion also produces surface tension

Mercury has a higher surface tension than water.

Adhesion is an attraction between molecules of different substances. Mercury has very low adhesive force. Water has large adhesive force.

The Nature of Solids The particles in a solid are more closely packed than those of a liquid or gas. Intermolecular forces between particles exert stronger effects in solids than liquids. Intermolecular forces tend to hold the particles of a solid in fixed positions. Solids do not flow and particles are have orderly arrangement. Particles in a solid vibrate in place. Solids have definite volume and definite shape. Incompressible!

In general, substances are most dense in the solid state. Solids tend to be slightly denser than liquids and much denser than gases. Because…..The particles are very closely packed.

Exception….water Solid water (ice) is less dense than liquid water. Ice floats!

There are two types of solids: Crystalline solids (most solids) Amorphous solids They consist of crystals. A crystal is a substance in which the particles are arranged in an orderly, geometric, repeating pattern. Examples: ionic compounds, metals, etc Examples: glass and plastics Their particles are arranged randomly.

There are four types of crystalline solids: Ionic solids: Metallic solids: Covalent-Network solids: Molecular solids:

Ionic solids: Made up of positive and negative ions and held together by electrostatic attractions. They have very high melting points, are hard and brittle, and are poor conductors in the solid state. NaCl

Metallic solids: Made up of metal cations in a sea of delocalized electrons. They have high melting points, can range from soft and malleable to very hard, and are good conductors of electricity. CopperTungston

Covalent-Network solids: Made up of atoms connected by covalent bonds to its neighboring atoms. The covalent bonding extends throughout a network that includes a very large number of atoms. They are very hard with very high melting points and are poor conductors. Diamond GraphiteQuartz, SiO 2

Molecular solids: Made molecules held together by intermolecular forces such as van der waals, dipole-dipole forces, or hydrogen bonds. They are relatively soft, have low melting points and are poor conductors. An example of a molecular solid is sucrose and ice.

There are 7 crystal systems:

CubicOrthorhombic Tetragonal

Monoclinic Triclinic Hexagonal Rhombohedral

Amorphous solids The atoms are not arranged in a regular pattern. Their atoms are randomly arranged.

Amorphous solids Plastic Rubber Asphalt Glass

Glass Components 72% silicon dioxide, SiO 2 (sand)

When crystalline solids melt…. Solid liquid

As a result of their irregular internal structure….. Glass does not melt at a definite temperature. Instead, glass gradually softens when heated. When a crystalline solid is shattered, the fragments have the same surface angles as the original solid. By contrast, when an amorphous solid like glass is shattered, the fragments Have irregular angles and jagged edges. Amorphous solids melt….gradually