Pure Substance Compound Element —matter that has a constant composition and distinct properties; differ from one another in composition Compound Element Substance composed of atoms from two or more elements chemically bonded in fixed proportions Differ by type of force (chemical bond) holding the atoms together Has properties different than its components Can be separated into components by only chemical means (electricity & heat) Substance that cannot be separated into simpler substances 3 categories: monatomic, diatomic, or polyatomic *Atom—smallest particle of an element that retains all properties of the element

Chemical Formula Express the composition of substances in terms of their chemical symbols Subscripts denote the number of atoms Subscripts outside parentheses get multiplied in Coefficients are multipliers

Compound Metallic Ionic Molecular Composed of cations held together by metallic bonds (sea of electrons) Composed of ions held together by ionic bonds Composed of molecules held together by intermolecular forces Molecules held together by covalent bonds *Molecule—two or more atoms covalently bonded as a discrete unit

urea Chalcopyrite gold ingots liquid nitrogen silicon crystals aluminum Elemental sulfur quartz dry ice – carbon dioxide lithium fluoride Copper urea

Allotrope —two or more different forms in which an element can exist; differ in physical and chemical properties

Mixture Heterogeneous Homogeneous —matter that is made from a combination of two or more pure substances where each pure substance retains its individual identity; do not have fixed proportions; created or separated by physical means Heterogeneous Homogeneous individual substances remain visually distinct Visibly indistinguishable parts (uniform appearance) Mixed at the molecular level Also called a solution

Alloy Substitutional Interstitial —combination of metals or metal and another element; has properties superior to its constituents Substitutional Interstitial Atoms of the added component(s) take up spaces that are normally occupied by atoms of the host element Similar in size Atoms of the added component(s) occupy spaces in between atoms of the host metal Discrepancy between atom sizes