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Solid: A state of matter with definite shape and volume; particles are close and vibrate in fixed positions. Liquid: State of matter with definite volume, no definite shape; particles are close but move more freely. Gas: State of matter without definite shape or volume; particles are far apart and move randomly. Pure Substance: Material with only one type of particle; can be elements or compounds. Element: Pure substance that cannot be chemically broken down; made of atoms and in the periodic table. Compound: Pure substance formed from two or more elements combining in fixed proportions; can be broken down chemically. Homogeneous Mixture: Uniform distribution of components throughout the mixture; same composition and properties in every part. Heterogeneous Mixture: Non-uniform distribution of components with varying composition and properties. Solution: Type of homogeneous mixture with dissolved solutes in a solvent; particles too small to see and do not separate. Chemical Change: Process where substances undergo chemical reactions and transform into new substances. Physical Change: Process where substances change physical properties without changing chemical composition.