Representing Matter The fundamental unit of matter is the atom. Greek-”unbreakable” A neutral group of atoms held together by chemical bonds is called a molecule
Matter cont. Elements are the simplest pure substances. Contain only one kind of atom. Each has their own set of physical and chemical properties Diatomic
Matter cont. If a molecule has at least two different kinds of atoms present then it is a compound
Classifying Matter Use the symbols of the elements Ag, Na, H2, NaCl, H2O, etc Subscripts tell how many of an atom is in the molecule H2O, H2SO4, CaCl2 Coefficientstell how many of the atom/molecule Ag, 2Na, 3H2, 4NaCl, 5H2O, etc
Pure Substances Fixed composition Cannot be separated into simpler substances by physical methods (physical changes) Can only be changed in identity and properties by chemical methods Properties do not vary
Mixtures Variable composition Components retain their characteristic properties May be separated into pure substances by physical methods Mixtures of different compositions may have widely different properties
Homogeneous Mixtures Homogenous mixtures look the same throughout but can be separated by physical means (dissolution, centrifuge, gravimetric filtering, etc.). Examples: milk, yogurt, solutions
Heterogeneous Mixtures Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).