Ch 18 Section 1

Composition of Matter

Pure Substance   Pure substance is a type of matter made with a

fixed composition.

  Substance can either be an element or a compound.

  Ex: helium, aluminum, water, and salt.

Element   All substances are built from atoms.

  If all the atoms are the same then the substance is an element.

  90 elements are found on earth

  More than 20 elements have been made in a laboratory.

Compounds   A pure substance in which two or more elements

are combined in a fixed proportion.

  Ex: salt (NaCl), water (H2O)

Molecules   Particles consisting of two or more atoms that are

bonded together.

Mixture   Heterogeneous Mixture- a mixture in which

materials can be distinguished easily.   Ex: pizza

  Homogeneous Mixture- a mixture in which the substances are mixed evenly throughout.

  Ex: Unopened soda

Solution   A homogeneous mixture with particles so small

that they will never settle to the bottom.

Colloids   A type of mixture with particles that are larger than

those in solutions but not heavy enough to settle out.

  Tyndall effect

Suspension   A heterogeneous mixture containing a liquid in

which visible particles settle.   Ex: Pond water