Matter is the fundamental substance that makes up everything in the universe. It is defined as anything that has mass and occupies space or volume. From the smallest atoms to the largest stars, everything we can see, touch, and interact with is made of matter. At the atomic level, matter consists of atoms with a nucleus containing protons and neutrons, surrounded by orbiting electrons.
Matter exists in four main states. In solids, particles are tightly packed in a fixed arrangement, giving solids their definite shape and volume. In liquids, particles are more loosely packed and can move around each other, allowing liquids to flow while maintaining a definite volume. In gases, particles are spread far apart and move freely, so gases expand to fill their container. Plasma is the fourth state, where gas particles become ionized, creating a highly energetic state found in stars and lightning.
Matter can be classified into pure substances and mixtures. Pure substances include elements, which contain only one type of atom like hydrogen gas, and compounds, which contain two or more different atoms chemically bonded together like water. Mixtures are combinations of two or more substances that are not chemically bonded. Homogeneous mixtures have uniform composition throughout, like salt water, while heterogeneous mixtures have non-uniform composition with visible boundaries between components, like oil and water.
Matter has physical and chemical properties. Physical properties like color, shape, density, and melting point can be observed without changing the substance's composition. When ice melts to water or water boils to steam, only the physical state changes. Chemical properties involve the substance's ability to undergo chemical reactions, like flammability or reactivity. When wood burns, it undergoes a chemical change, forming new substances like ash and carbon dioxide with different properties than the original wood.