Matter is the physical substance of the universe, underpinning all of science. Defined simply, matter is anything that has mass and takes up space, which is referred to as volume. All objects we can touch, see, or feel, from the air we breathe to the stars, are composed of matter. Understanding the fundamental nature of this substance reveals how our world is constructed and how it behaves.
What Matter Is Made Of
The basic building block of all matter is the atom, the smallest unit that retains the chemical properties of an element. Atoms are comprised of three primary subatomic particles: protons, neutrons, and electrons. Protons carry a positive electrical charge, and neutrons carry no charge; both reside together in the dense, central nucleus.
The mass of an atom is largely determined by the total number of protons and neutrons within this nucleus. Far outside the nucleus, the much lighter, negatively charged electrons orbit in a cloud-like region. The interaction between the positively charged protons and the negatively charged electrons holds the atom together.
Pure substances consisting of only one type of atom are known as elements, such as gold or oxygen. Atoms bond chemically to form larger structures called molecules. A molecule is formed when two or more atoms join, and they can be made of the same type of atom, like oxygen gas, or different types, such as a water molecule (two hydrogen atoms and one oxygen atom).
The Observable States of Matter
Matter exists in distinct forms, referred to as states or phases, determined by the arrangement and energy of its component particles. The four most commonly observed states in everyday life are solid, liquid, gas, and plasma.
In a solid, particles are packed tightly together in fixed positions, allowing them only to vibrate in place, giving the substance a definite shape and volume. Liquid particles remain close together but are not held rigidly, allowing them to slide past one another. This characteristic grants liquids a fixed volume but enables them to take the shape of any container they occupy.
Gas particles are far apart and move freely and rapidly, causing a gas to expand and fill both the shape and volume of its container completely.
Plasma is considered the fourth state of matter. It is similar to a gas but consists of highly charged particles. This state occurs when a gas is heated to extremely high temperatures, causing the atoms to become ionized. Stars, including our Sun, are superheated spheres of plasma, making this the most abundant form of ordinary matter in the universe.
Physical and Chemical Properties
Matter is described using properties that help distinguish one substance from another. These descriptive qualities are separated into two categories based on whether observing them changes the substance’s fundamental identity.
Physical properties are characteristics that can be observed or measured without altering the composition of the substance. Examples of physical properties include color, density, mass, melting point, and boiling point. When water freezes into ice, its state changes, but its fundamental molecular composition remains water (H2O).
Chemical properties, in contrast, are characteristics that describe a substance’s ability to undergo a change that results in a new substance. These properties can only be observed when matter is actually undergoing a chemical change. Flammability, the ability to burn, is a chemical property because the process of burning transforms the original substance into entirely different compounds like ash, carbon dioxide, and water vapor. Reactivity, which describes how a substance interacts with others, and the tendency of a metal to rust (oxidation) are also examples of chemical properties.
Matter Changes But Is Never Lost
Matter constantly undergoes transformations, classified as either physical or chemical changes. A physical change involves the alteration of a substance’s appearance, such as melting or breaking, without changing its molecular structure. A chemical change, like cooking an egg or burning wood, results in the formation of one or more entirely new substances.
A fundamental principle governing all these transformations is the Law of Conservation of Mass. This law states that for any closed system, the total mass remains constant, regardless of whether a physical or chemical change occurs. Mass is neither created nor destroyed during these processes; it is simply rearranged into different forms.
For example, when a piece of wood is burned, the mass of the resulting ash, smoke, and gases precisely equals the mass of the original wood plus the oxygen consumed from the air. The atoms are conserved throughout the reaction, merely combining in new ways to form different molecules.