States of Matter

Matter can exist in three different physical forms—solid, liquid or gas. We are all familiar with the forms of water—ice, liquid water and steam. These different forms are called the states of matter. The particles within matter interact with each other in different ways and determine if the matter is a solid, liquid or gas.

Solid matter has a definite shape and volume. Think about a bowling ball. You can pick it up, move it and drop it, and the shape always remains the same. The ball is a solid. The particles that make up a solid are packed tightly together in a fixed position. The particles themselves vibrate, but they do not move out of position.

Solids can be classified as crystalline or amorphous. In crystalline solids, such as quartz or salt, the particles have a regular repeated pattern and a definite geometric shape. When crystalline solids are heated, they have a precise melting point. Amorphous solids, such as glass and rubber, are made up of particles that are arranged randomly, and they do not have a precise melting point.

Liquid matter can change its shape, but it always has a definite volume. For example, if you pour 200 ml of milk from a carton into a measuring cup and an equal amount into a flask, the shape of the liquid will be different in the two containers, but the volume will stay the same. Similar to a solid, the particles in a liquid are packed closely together. However, unlike a solid, the particles in a liquid can slide past each other. This sliding motion allows a liquid to flow, or be fluid, and take on the shape of its container.

Many liquids, such as water, form droplets. These droplets are caused by surface tension, which occurs when the molecules at the surface of the liquid form a strong attraction to each other and to the water molecules below them. This attraction can form a layer on the surface of the liquid. Surface tension is what allows lightweight insects to actually walk across the surface of a pond. The surface tension of different liquids varies. For example, alcohol has a lower surface tension than water.

Viscosity is a property of liquids. Basically, viscosity means a liquid’s resistance to flow. Liquids with higher viscosity flow more slowly, like honey. Liquids with lower viscosity flow more quickly, like water. Here are some other examples of liquids and their relative viscosities.

Gas particles move in all directions, and are only limited by the container they are in. Unlike solids and liquids, gas particles have a lot of empty space between them. Gases can change both shape and volume. Scientists discovered that the temperature, volume and pressure of a gas are all related. Changing one of these factors, affects the other factors.

Robert Boyle was a scientist that studied gases and the relationship between pressure and volume. Boyle’s law states that, for a gas that is at a constant temperature, the volume is inversely related to the pressure. An example of Boyle’s Law in action is the increasing volume of bubbles as they rise from an area of high pressure to an area of low pressure. A scuba diver at the bottom of the ocean releases air bubbles. As the bubbles rise, the pressure inside the bubbles decreases. This decrease in pressure results in an increase in volume within the air bubbles, and the bubbles get larger.

In the late 1700s a scientist and inventor named Jacques Charles helped create the first hydrogen-filled balloons. He discovered that the volume of a gas, such as hydrogen, will increase as the temperature of the gas is increased. Charles’s Law states that, for a fixed amount of gas at a constant pressure, the volume will change in direct proportion to a change in temperature. For instance, in a hot air balloon, as the gas inside the balloon is heated and the temperature increases, the volume of the gas expands, and the balloon gets larger.