Chemistry Studies Matter’s Composition and Properties Chemistry examines matter, focusing on what substances are made of and how they behave. It relates composition to properties, connecting structure to observable qualities. Changes and interactions among substances reveal underlying rules. Understanding matter’s makeup explains its behavior in everyday and scientific contexts.
Matter Has Mass, Occupies Space, and Interacts Matter consists of anything with mass that occupies space. Properties arise from the substances’ composition. Interactions among substances determine how they combine or remain separate. Observations of properties and interactions guide classification.
Physical Classification Relies on State: Solid, Liquid, Gas Matter appears as solids, liquids, or gases. Each state differs by shape and volume behavior. Recognizing state helps predict how a substance will respond to containers and handling. This forms the basis of physical classification.
Solids Maintain Definite Shape and Volume Solids resist shape change and maintain fixed volume. Their form remains independent of the container. Examples include iron. Stability characterizes this state.
Liquids Keep Volume but Take the Container’s Shape Liquids have definite volume but no fixed shape. They flow and adapt to the container that holds them. Water and oil illustrate this behavior in everyday use. The surface adjusts while the quantity remains constant.
Gases Lack Definite Shape and Volume Gases expand to fill any container. They have neither fixed shape nor fixed volume. Hydrogen and nitrogen exemplify common gases. Their extent depends on the space available.
Chemical Classification Distinguishes Pure Substances and Mixtures Beyond state, substances are organized by composition. Materials with a single, fixed makeup are pure substances. Combinations with variable makeup are mixtures. This division explains consistency versus variability in samples.
Pure Substances Exhibit Fixed Composition and Identical Particles A pure substance contains only one kind of particle. Its composition remains constant from sample to sample. Properties reflect that uniform makeup. Predictable behavior follows from this fixed identity.
Elements Are Pure Substances of One Kind of Atom An element cannot be broken into simpler substances by chemical means. Each element consists of only one type of atom. Examples include gold, silver, hydrogen, and nitrogen. Elemental identity defines characteristic properties.
Metals Show Lustre and Conduct Heat and Electricity Metals typically appear shiny with metallic lustre. They conduct heat and electricity effectively. They are generally solids under ordinary conditions. These traits distinguish them within the elements.
Nonmetals Are Poor Conductors and Often Non-Lustrous Nonmetals lack metallic lustre. They do not conduct heat and electricity well. Many occur as gases under ordinary conditions. Their behavior contrasts with metals in everyday observations.
Compounds Form by Combining Elements in Fixed Proportions A compound is produced when different elements combine chemically in definite ratios. The resulting substance has its own distinct properties. Composition remains the same across all samples of the compound. Fixed proportion is a defining feature.
Molecules Contain Specific Numbers of Different Atoms Molecules of a compound embody the fixed ratio of its elements. Water contains two hydrogen atoms and one oxygen atom. Carbon dioxide contains one carbon atom and two oxygen atoms. The count of atoms per molecule remains constant.
Atomic Mass Provides a Basis for Counting Atoms Each element has a characteristic atomic mass. Common reference values include carbon at 12 and oxygen at 16. These numbers allow quantitative description of composition. Atomic masses underpin calculations involving molecules.
Molecular Mass Equals the Sum of Atomic Masses A molecule’s mass is the total of the atomic masses of its constituent atoms. For carbon dioxide, one carbon (12) plus two oxygens (16 each) gives 44. This method generalizes to any compound. Mass accounting reflects the fixed composition.
Organic Compounds Center on Carbon Organic compounds are defined by the presence of carbon. Classification distinguishes organic compounds as a major type. Carbon-containing substances fall under this group. This label sets them apart in the scheme of compounds.
Inorganic Compounds Include the Remaining Non-Carbon Types Inorganic compounds include those beyond the organic group. Classification pairs organic with inorganic to cover compounds. Their compositions are built from various elements. This division keeps compound types distinct.
Mixtures Combine Substances Physically Without Fixed Ratios A mixture contains two or more substances brought together without chemical bonding. Composition can vary by proportion. Components retain their individual properties. The makeup depends on how much of each part is present.
Mixtures Differ from Compounds in Composition and Identity Compounds have fixed composition and new properties distinct from their elements. Mixtures show variable composition and preserve component traits. This contrast separates chemical combination from physical blending. Identity change marks compounds, not mixtures.
Homogeneous Mixtures Display Uniform Composition Throughout A homogeneous mixture looks the same in every portion. Solutions are prime examples. Sugar dissolved in water illustrates uniform distribution. No visible boundaries appear within the mixture.
Heterogeneous Mixtures Show Non-Uniform Regions A heterogeneous mixture contains visibly different parts. Oil and water form separate layers instead of blending uniformly. Composition varies from place to place. Distinct phases mark this category.
Solutions Exemplify Even Mixing with Sugar in Water Sugar mixed in water exemplifies a solution with even distribution. The mixture looks uniform across the container. No separate layers appear. This uniformity marks the type.
Visual and Compositional Clues Distinguish Mixture Types Uniform appearance suggests a homogeneous mixture, while visible separation indicates a heterogeneous one. Consistent composition across samples supports homogeneity. Observable layers or clusters reveal non-uniformity. These clues guide quick identification.
Matter’s Full Classification Links State and Composition Matter is described by state—solid, liquid, or gas—and by composition—pure substance or mixture. Pure substances divide into elements and compounds. Mixtures divide into homogeneous and heterogeneous forms. This map organizes observations into a coherent scheme.
Exam-Oriented Focus on Definitions, Properties, and Examples Clear definitions of state, element, compound, and mixture anchor understanding. Properties such as metallic lustre and electrical conductivity help classify elements. Examples like hydrogen, nitrogen, water, and oil–water illustrate the categories. Diagrams or overviews of classification are commonly expected in assessments.