Chapter 6.1: Organizing the Elements The Periodic Table Chapter 6.1: Organizing the Elements

The discovery of the scientific method caused an increase in the rate of discovery of elements

J.W. Dobereiner Published a classification system of triads. Elements grouped in sets of three with similar characteristics (chemical properties). Problem: All known elements couldn’t be grouped into triads.

Dmitri Mendeleev 1869: Published a new periodic table arranging the elements in increasing atomic mass. Predicted elements (and properties) would fill spaces he left in his table.

Modern Periodic Table

Mendeleev made his table before knowledge of protons identifying an atom. The modern periodic table arranges elements in increasing atomic number. Elements with similar properties are located in the same column (group/family).

Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

Three Classes of Elements Metals Nonmetals Metalloids Based on their general properties

Location on Periodic Table Metals (blue) = LEFT of stair step Nonmetals (yellow) = RIGHT of stair step Metalloids (pink) = TOUCHING stair step

Metals Most elements Good conductors of heat and electric current High luster/sheen Solid at room temperature (not mercury) Many ductile (can be made into wires) Most malleable (can be hammered into thin sheets without breaking)

Nonmetals Greater variation in properties than metals Most gases at room temperature NOT metals Tend to have properties that are opposite of metals Poor conductors of heat and electric current Solid nonmetals tend to be brittle

Metalloids Have properties that are similar to metals and nonmetals (based on conditions like temperature, presence of other elements, etc.)