Elements and Compounds

Pure Substance What does pure mean? Unmixed All the same Uniform A substance in which there is only one type of particle

Element A pure substance that cannot be separated into simpler substances by physical or chemical means MUST be on the periodic table Gold – Au Oxygen – O Helium - He

Element or Not? Lead? Sugar? Steel? Brass? Water? Salt? Copper? Yes! #82 Steel? Brass? No Water? Salt? Copper? Chlorine? Yes! #29 Yes! #17

Elements Each element has it’s own properties Such as boiling point, melting point and density Sodium Chlorine

Categories of Elements Metals Shiny Good conductors of heat and electricity Malleable (sheets) and ductile (wires) Most are solids

Categories of Elements Nonmetals Dull (not shiny) Poor conductors Brittle Nonmalleable Most are gas

Categories of Elements Metalloids Dull or shiny Semi-conductors Somewhat malleable and ductile

Compounds A substance with 2 or more elements combined in a definite ratio

Compounds A definite ratio does not change O2 vs. CO2 CO2 vs. CO

Sodium Chloride (Salt) Compounds Compounds have a unique set of properties Different than the elements that make it up + = Sodium Chlorine Sodium Chloride (Salt)

Molecules A molecule is formed when two or more atoms combine chemically. All compounds are molecules but not all molecules are compounds. H2 – Hydrogen – this is a molecule but not a compound H2O – Water – this is a compound