Early attempts to organize elements included grouping them into triads based on similar properties or by increasing atomic mass, seeing a periodic pattern. The modern periodic table arranges elements by increasing atomic number, reflecting a periodic repetition of physical and chemical properties. Elements are classified as metals, nonmetals, or metalloids based on their general conductive properties and whether they are solids, gases, or have properties in between.

1. Section 1:Organizing the Elements

2.  Compare early attempts at organizing the
elements to the modern periodic table;
 Explain how elements are arranged in the
modern periodic table; and
 Identify three broad classes of elements and
their properties.

3.  First attempts to organize elements was
based on their properties
 J.W. Dobereiner organized them into triads
◦ Groups of three elements with similar properties
◦ Middle element had properties that were between
the other two
 Example: Cl, Br, I

4.  Dimitri Mendeleev organized elements by
increasing atomic mass
◦ Saw periodic, repeating pattern of properties
◦ Also had holes for undiscovered elements
◦ When they were discovered, matched his
predictions

5.  Predicted two
elements
between Zn & As
 When Ga & Ge
discovered,
matched his
prediction

6.  Periodic law: when elements arranged by
increasing atomic number, there is a periodic
repetition of their physical and chemical
properties
◦ Holds for all elements, unlike Dobereiner
◦ Differs from Mendeleev, who used atomic mass

7.  Metals
 Nonmetals
 Metalloids
 Based on their general properties

8.  ~80 % of elements
 Good conductors of heat & electric currents
 High luster (shiny)
◦ Ability to reflect light
 Solid at RT
◦ Except Hg (mercury)
 Ductile—can form wires
 Malleable—can make thin sheets without
breaking

9.  Found in the upper right corner.
 Most are gases at RT
◦ N, O
 A few are solids
◦ Sulfur & Phosphorus
 1 liquid
◦ Br

10.  Poor conductors
◦ Except Carbon
 Brittle—will shatter if hit

11.  Properties of both metals & nonmetals
 Depends on the conditions
 Example Silicon
◦ Poor conductor
◦ Add small amount of boron—now a good conductor

13.  Compare early attempts at organizing the
elements to the modern periodic table?
 Explain how elements are arranged in the
modern periodic table?
 Identify three broad classes of elements and
their properties?

14.  Page 160, # 1-7