Describing and Classifying Matter

Describing Matter

Each type of matter has its own unique properties. A property is a characteristic or trait people use to identify matter. The properties of matter allow us to identify different substances. For example, we use the properties of matter to know that wood is wood and gold is gold. The properties of matter fall into two categories. These are physical properties and chemical properties.

Physical Properties

A physical property is a characteristic of matter that describes its physical form. We often use our senses to identify physical properties. You can see colour and luster. Luster is how shiny or reflective something is. You can smell odour. You can taste things like acidity. You can feel texture, hardness and temperature. You can try to flatten things to test their malleability. Any you can try to stretch things out to test their ductility.

Some properties you cannot identify with your senses. These include things like boiling point and melting point. These are specific temperatures when matter changes state. Electrical conductivity, magnetism and density are also physical properties.

Physical properties can be either intensive or extensive. An intensive property is a property that does not depend on the amount of matter. Examples of this are colour, odour, density and melting point. An extensive property is a property that depends on the amount of matter. Examples of this include mass, volume and length.

Chemical Properties

The chemical properties of a substance predict whether a chemical reaction will happen. The following are examples of chemical properties.

Flammability

Is the ability to burn or combust. Things that are flammable can ignite easily and burn quickly. Flammable materials are often called fuel.

Wood, gasoline and wax are all things that are flammable.

Corrosiveness

Is the ability to ‘eat away’ another substance. It is important to wear safety equipment on skin and eyes when using corrosive materials.

Corrosive materials include strong acids and bases. Hydrochloric acid and bleach are two examples.

Toxicity

Is the ability of a material to cause damage to living things. Toxic materials cause harm when inhaled, swallowed or contact skin.

Lead, mercury and chlorine gas are toxic.

Classifying Matter

There are different ways to classify matter. One way is classifying matter as a pure substance or a mixture.

Pure Substances

A pure substance is the same throughout. Pure substances cannot be separated into other pure substances by physical means. Water is a pure substance. The physical properties of a pure substance never change. For example, the melting point of ice is always zero degrees Celsius at a pressure of 101.3 kilopascals.

Pure substances only contain one type of element or compound. Elements are substances that contain only one type of atom. Examples of elements are carbon (C), silver (Ag) and gold (Au). Currently, there are 118 known elements. Several of these elements were discovered during your lifetime!

Scientists have organized the elements into a table called the Periodic Table of the Elements. This is often shortened in everyday language to the Periodic Table.

Each element of the periodic table has a set of specific characteristics that are unique to it. These are called characteristic properties. These allow us to identify and classify each element. Characteristic properties are all extensive properties. These include density, melting point, boiling point, electronegativity and atomic weight.

Compounds are substances formed by the joining together of two or more elements. In a compound, the elements are chemically held together in a fixed ratio. Water, for example, is a compound made up of two hydrogen atoms (H) and one oxygen atom (O). Compounds can be broken down into their individual elements by chemical means. For example, water can be broken down into hydrogen and oxygen through electrolysis. The properties of a compound are different from the properties of the elements that form it. Water has very different properties than hydrogen and oxygen.

A molecule can be an element if it only has the same type of atoms, such as O2, the natural form of oxygen. Or it can be a compound, such as carbon dioxide, CO2.

Mixtures

Mixtures are a combination of two or more pure substances. When mixed together each pure substance retains its own properties. For example, salt water does not have the same properties as either salt or water. Mixtures can be either homogeneous or heterogeneous.

A homogeneous mixture is a mixture that is completely uniform in composition. Salt water is a good example of a homogeneous mixture. Another name for a homogeneous mixture is a solution. Solutions are not only made of liquids. There are solutions made of gases, such as air. There are also solutions made of solids. Alloys are solutions of metals, such as bronze or brass.

A heterogeneous mixture is a mixture that is not the same throughout. It is a mixture in which the individual parts can be seen. Examples of heterogeneous mixtures include oil and vinegar salad dressing and mixed nuts.