When a chemist talks about properties they are referring to a substance’s characteristic qualities that distinguish that substance from other things. The more properties that we can assign to a substance the better we understand that substance and can easily identify and predict its behavior in different circumstances. We can then group substances by their properties and reasonably expect that things with similar properties will behave in the same way under the same circumstances. There are two large categories that chemists divide properties into: physical properties, and chemical properties.
Physical properties can be observed without changing the fundamental structure of a thing that you are observing. Physical properties are the things that you can learn by picking something up and interrogating it with your senses. However, we must be careful to distinguish physical properties of an object with physical properties of the material that object is made of. Properties of objects will depend on the size and shape of that object. For instance, a large solid glass sphere will weigh more than a smaller solid glass sphere.
We call properties that are inherent to the object, but not inherent to the material extensive properties, such as mass, volume, or temperature. On the other hand, properties that are inherent to the material no matter its size or shape are called intensive properties. Going back to our example of the two glass spheres; the larger sphere has more mass, and therefore weighs more, but both spheres have the same density as long as they are made from the same material. Thus, one cubic centimeter from the first sphere weighs the same as a cubic centimeter from the second sphere. Some other intensive properties include: color, conductivity, melting/boiling point, magnetic permeability, etc. Since chemists don’t care about objects and are instead interested in how materials interact, they tend to pay much more attention to intensive properties than extensive properties.
All mater can exist in various states. A state is usually determined by how weakly or strongly particles are interacting with each other. For every substance, it’s characteristics will be different depending on what state it is in. The conditions required to change from one state to another are different for different kinds of matter, and are listed among a substances physical properties (boiling point and melting point being the two most commonly used). There are three states of matter which are commonly experienced by humans: solid, liquid, and gas. Although other states such as plasma exist, we’ll only focus on these three for now.
When a substance is in its solid state it is characterized by the fixed shape. The molecules of an object in a solid state have strong interactions with each other. The atoms in a solid state are so tightly packed that they cannot move freely, but merely vibrate. As a result, the material to keep a fixed, rigid shape.
A solid can be converted into a liquid by rising the temperature to above that substances melting point. Rising the temperature causes the intermolecular interaction that were holding molecules in place to break and let molecules move around. Thus, molecules in a liquid state have much weaker interactions with each other than in a solid state. The atoms in a liquid state can move around each other but they still constantly interact. As a result, liquids have a definite volume but no ridged shape (fits the shape of the container).
A liquid can be turned into a gas by increasing the temperature to above that materials boiling point. Molecules in a gaseous state have very low interactions with each other. The atoms in a gasous state have almost no association with each other and move freely and in random directions. As a result, gasses are compressible (have no definite volume), and fit the shape of their container, filling it completely.
A mixture is two or more distinct substances blended together. As such they can be separated using only physical means. This means that the properties of the two substances remain separate from each other even though the two substances are mixed.
There are two classes of mixtures based on how uniformly the substances are distributed through the mixture. Homogenous mixtures have substances evenly distributed throughout the mixture so that any section will contain the same proportion of substances as any other section of the mixture. A homogeneous mixture is uniformed throughout the mixture too. This means that no physical separation between the components of the mixture exists.
An example of a homogenous mixture could be sugar dissolved in a glass of water. The sugar is evenly distributed in the water so that any volume of water taken from the glass would also contain a set ratio of sugar. Also, you cannot “see” sugar pieces separately no matter how closely you look. However, the two substances can still be separated by evaporating water which can be later condensed back to a liquid form. Thus, you’ll have a separate container with your original water and another one with sugar.
A heterogeneous mixture consists of two or more immiscible substances that do not make a uniform mixture. Essentially, the substances exist in different states and since the substances do not blend together, we can still see them individually. A typical example of such a mixture would be oil and water mixed together. An example of a heterogeneous mixture that is not composed of liquid would be a salad. Even after all the parts of the salad have been mixed together there are still chunks of tomato and chunks of lettuce and the ratio of tomato to lettuce is not the same through the salad.
While physical properties are evident simply by observing the object, chemical properties only become apparent after a chemical reaction. When a substance has undergone a chemical reaction the structure of the molecules making up a substance will change drastically and will not be able to be reversed until another chemical reaction occurs. Chemists express these changes by drawing chemical equations and chemical reactions. Some examples of chemical properties include: flammability, chemical stability, oxidation states, and many others. Compounds can only be separated into different substances using chemical properties and not physical properties.
Chemistry is the science of understanding the changes that matter can experience. Because of this, chemists have developed an extensive vocabulary to describe matter and its different properties. In this lesson, we have given you the tools to you need to begin your inquiry into the chemical foundations of the world around you. The relationships might seem complicated at first but will become quite familiar as you progress and use them more often. Until that time, we have provided a flow chart below to help you keep track of the multi-layer classification of matter.