Classification of Matter Definitions

Pure Substances A pure substance has its own characteristic properties. All samples of a substance will have the same properties while at the same conditions – Elements – Compounds

Elements 110 known elements Each element has its own characteristic properties Cannot be broken down by ordinary chemical means Divided by properties into metals, nonmetals and metalloids (properties of both metals and nonmetals)

Compounds Two or more elements chemically combined to form a new substance with its own set of physical and chemical properties 2H 2 + O 2 → 2H 2 O A compound may be broken down by chemical means into its constituent elements 2H 2 O → 2H 2 + O 2

Physical Properties Properties which can be observed and measured without the production of new substances Metals – Conduct electricity and heat energy – Some are Malleable (hammered into shapes) – Some are Ductile (Can be drawn into wires)

Other physical properties Density (mass per unit of volume) or D=m/v Hardness Solubility or insolubility Boiling/melting points

Physical Properties III - A physical change does not change the identity of a substance - Physical properties are dependent on temperature, pressure, and phase. - Molten lead is less dense than solid lead - Boiling point depends on atmospheric pressure (Water boils at 93°C in Denver) - Ice is less dense than water, because of the crystalline structure of water as it freezes - Ice floats on water

Chemical Properties How a substance interacts with other substances (or fails to react) Rusting of iron (iron reacts with water to form iron oxide Relative inertness of nitrogen (does not react with most other substances) A chemical change results in the formation of a new substance

Mixtures Mixtures can have their own set of properties, and these properties can change as the mixture changes. The boiling point of a salt/water solution is dependent on the concentration of salt.