Use particle models to explain why liquids and gases take the shape of their containers.

The world around us is filled with materials that are constantly in one of three primary states of matter: solids, liquids, and gases. Understanding these states is fundamental in grasping the behavior of different materials. The states of matter are characterized by distinct physical properties, primarily defined by how the matter's particles are arranged and how they move.

In solids, particles are closely packed together in a fixed, orderly arrangement, leading to a rigid structure with a definite shape and volume. Moving to liquids, the particles are still close together but are not in a fixed arrangement, which allows liquids to flow and take the shape of their container while maintaining a constant volume. Gases have particles that are very far apart and move freely at high speeds, resulting in a state that has neither fixed shape nor fixed volume. Gases expand to fill their container completely.

At a micro level, transitions between these states occur due to changes in temperature and pressure, which affect the energy and movement of the particles. For example, heating can turn solids into liquids (melting) and liquids into gases (vaporization), while cooling can cause gases to condense into liquids and liquids to solidify into solids.

Liquids are fascinating in that they possess qualities of both solids and gases, making them unique in the way they behave. One of the fundamental properties of liquids is their ability to flow. This fluidity is a direct result of the spacing and energy of their particles.

Unlike in a solid, the particles in a liquid are not bound in a fixed shape, allowing them to move past one another with ease. This gives liquids the characteristic ability to adapt to the shape of their containers, a concept well-observed when pouring water into different-shaped glasses. However, despite their fluid nature, liquids do have a fixed volume and they do not expand to fill their container.

Liquids also have a property known as viscosity, which is a measure of their ability to resist flow. Honey, for example, has a higher viscosity than water and flows much more slowly. Surface tension is another important property of liquids, caused by the cohesive forces between liquid molecules, which accounts for the phenomenon of water droplets forming beads on surfaces.

When we consider the properties of gases, we're looking at a state of matter that is much less defined than solids or liquids. Gas particles have a lot of energy compared to those in the other states of matter, enabling them to move in random directions at high speeds.

The primary property of gases is that they have no fixed shape or volume. Instead, they spread out indefinitely to completely fill the container they are in, pushing against its walls; this is known as the gas's pressure. Gas pressure increases with the number of particles in a given space and with the temperature, as higher temperatures give the particles more energy to move.

Gases are also highly compressible due to the large amounts of space between particles. This compression is what allows gases to be stored in gas cylinders for various uses. Diffusion is another property of gases, which refers to the spreading of gas particles until they are evenly distributed throughout a space, resulting from their constant and random motion.