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

• Coefficients tell 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).