Elements and Their Properties Unit 1-Activity 2

What is an element? ◦ A material that cannot be broken down into new material that is stable or simpler through a chemical reaction What is a compound? ◦ a substance that consists of at least two different kinds of atoms

The periodic table organizes the list of known elements by using physical and chemical properties of those elements Physical Properties ◦ Characteristics that can be measured and observed without the substance undergoing any change in composition ◦ Examples: color, odor, texture, density, melting and boiling points Chemical Properties ◦ characteristics that change the identity of a substance when observed ◦ Examples: flammability, tendency to rust, explosiveness

History of the Periodic Table Dimitri Mendeleev organized the first periodic table based on the increasing atomic mass. Henry Moseley reorganized the periodic table by increasing atomic number.

The periodic table is setup into periods (rows) and groups (columns) ◦ Elements in the same family (group) will have similar physical and chemical properties

The elements in the periodic table can be classified into three groups :metals, nonmetals, metalloids Metals:to the left of zigzag line. ◦ Generally solids that have the following properties  Luster (shininess)  Malleable (ability to be hammered into thin sheets)  Good conductor of heat and electricity  May react with acids  Ductile (ability to be pulled into wire)

Nonmetals:to the right of the zigzag line. ◦ Have a wide range of properties  Can be dull and brittle  Can be solid, liquid or gas  Most are poor conductors of heat and electricity  Do not tend to react with acids Metalloids ◦ Found between metals and nonmetals (along stair-step line) ◦ Have properties of both metals and nonmetals

Another way to determine if an element is a metal or nonmetal is look at the pH of its oxide ◦ Oxide: when an element combines with oxygen  Metal oxides (metal + oxygen) --- ex: CaO  Nonmetal oxide (nonmetal + oxygen) --- ex: NO 2 ◦ pH: a way of describing how acidic or basic a solution is  pH = 7  neutral solution  pH less than 7  acidic  pH greater than 7  basic

Metal oxides in water ◦ Most have a pH greater than 7 (base) Nonmetal oxides in water ◦ Most have a pH less than 7 (acid)