Final answer:
Matter is classified into solids, liquids, and gases based on physical state, and as elements, compounds, and mixtures based on composition. The law of conservation of matter applies, and atoms and molecules are the basic units of matter.
Step-by-step explanation:
Phases and Classification of Matter
Matter can be classified into several categories based on its physical state and composition. The three primary physical states of matter are solid, liquid, and gas. Solids, like quartz, have a fixed shape and volume. Liquids, such as water, have a fixed volume but take the shape of the container they are in. Gases, like nitrogen dioxide, have neither fixed shape nor volume, and they fill the entire space available to them.
When classifying matter by composition, we encounter elements, compounds, and mixtures. Elements consist of only one type of atom, such as oxygen or gold. Compounds are substances composed of two or more elements chemically bonded, like water (H2O) or carbon dioxide (CO2). There are also mixtures which can be homogeneous or heterogeneous; a homogeneous mixture has a uniform composition throughout, like salt dissolved in water, while a heterogeneous mixture has visibly different parts, such as a salad or a rock with different minerals.
Matter is also subject to the law of conservation of matter, which states that in a closed system, matter is neither created nor destroyed, but it can change forms. To describe matter at the most basic level, we use the concepts of atoms and molecules. Atoms are the smallest units of an element that retain all the properties of that element, while molecules are groups of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.