Question

List six properties of solids, and explain each in terms of the kinetic- molecular theory of solids.

Short answer

The six properties of solids are high density, definite shape and volume, low compressibility, high melting and boiling points, strong intermolecular forces, and vibrational motion of particles.

Step-by-step solution

- Define the Kinetic-Molecular Theory of Solids

The kinetic-molecular theory of solids states that the particles (atoms, molecules, or ions) in a solid are closely packed together and vibrate about fixed positions. This explains the properties of solids based on the arrangement and motion of their particles.

- High Density

Solids typically have high density because their particles are tightly packed together in a fixed, orderly pattern. The close arrangement reduces the amount of empty space between particles.

- Definite Shape and Volume

Solids maintain a definite shape and volume because the particles vibrate but do not move from their fixed positions. This rigid arrangement prevents solids from flowing or changing shape unless forced.

- Low Compressibility

Since the particles in a solid are already close together, there is very little space to reduce, making solids low in compressibility. Applying pressure does not significantly reduce the volume of a solid.

- High Melting and Boiling Points

Solids generally have high melting and boiling points because a considerable amount of energy is required to overcome the strong intermolecular forces holding the particles in their fixed positions.

- Strong Intermolecular Forces

In solids, the forces between particles (intermolecular forces) are strong, causing the particles to remain in a fixed and orderly arrangement. This contributes to the overall stability of the solid's structure.

- Vibrational Motion

Particles in a solid exhibit vibrational motion about their fixed positions. These vibrations increase with temperature, but the particles do not move freely as they do in liquids or gases.

Key concepts

Kinetic-Molecular Theory of Solids

The kinetic-molecular theory of solids explains the properties of solids by focusing on the behavior and arrangement of their particles. In a solid, particles such as atoms, molecules, or ions are packed closely together, allowing only vibrational motion. They vibrate about fixed positions, but unlike in liquids or gases, they do not move freely. This fixed, orderly arrangement forms the foundation for understanding other properties of solids.

High Density

One defining characteristic of solids is their high density. The particles in a solid are packed tightly in a fixed structure, leaving minimal empty space between them. This dense packing results in a higher mass per unit volume. For example:

• Metals like iron and gold have high densities because their atoms are closely packed in a crystalline structure.
• The high density is also why solids tend to be heavier and more substantial than gases or liquids of similar volume.

Definite Shape and Volume

Solids have a definite shape and volume due to the fixed positions of their particles. Unlike liquids and gases, the particles in a solid do not flow or separate easily.

• A block of ice retains its rectangular shape without the need for a container, illustrating the fixed arrangement of its molecules.
• Even when a solid is broken or cut, each piece retains its volume and shape.

This property is crucial in many applications, such as construction materials and manufacturing.

Low Compressibility

The low compressibility of solids means they cannot be easily compressed into a smaller volume. Due to the minimal space between particles,

• Applying pressure doesn’t significantly change the volume of a solid.
• This property makes solids ideal for bearing loads and structural applications where maintaining shape under pressure is essential.

An example is how diamond, one of the hardest known materials, remains uncompressed even under enormous pressure.

High Melting and Boiling Points

Solids generally have high melting and boiling points. This is due to the substantial amount of energy required to break the strong intermolecular forces holding the particles in place.

• Melting ice into water requires heat to disrupt the hydrogen bonds between water molecules.
• Metals like tungsten have very high melting points, making them useful for applications that involve extreme temperatures.

This property ensures solids remain intact over a wide range of temperatures.

Strong Intermolecular Forces

The stability and structure of a solid are due to the strong intermolecular forces acting between its particles. These forces can be:

• Ionic bonds, like in table salt (NaCl), holding together positive and negative ions.
• Covalent bonds in diamonds, where carbon atoms share electrons.

The strength of these interactions ensures that solids maintain their form and resist external forces, making them crucial in construction and tools.

Vibrational Motion

In solids, particles primarily exhibit vibrational motion. Although fixed in place, they continuously vibrate within their positions.

• As temperature increases, the intensity of these vibrations also increases.
• This vibration does not allow the particles to break free from their fixed positions, unlike in liquids or gases.

A good example is how heating a metal rod increases the motion of its atoms, causing it to expand slightly, but not enough to turn it into a liquid or gas immediately.