1. 5.1: History of the Periodic Table 5.2: Periodic Properties

2. Mendeleev Noticed that when elements are arranged in order of increasing atomic mass, certain similarities in their chemical properties appeared at regular intervals He first organized a table where elements with similar properties were grouped together. This left several empty spaces and he therefore predicted the existence of several elements and their properties. Within 15 years they were all discovered (Sc, Ga, Ge).

3. Moseley He found that elements fit into patterns better when they were arranged in increasing order of their nuclear charge, or the number of protons. His work led to the recognition that atomic number not atomic mass is the basis for the organization of the periodic table. Periodic Law = the physical and chemical properties of the elements are periodic functions of their atomic numbers.

4. The Modern Periodic Table The period of an element is determined by its electron configuration. S-block: Group 1 and Group 2 – Chemically reactive – Group 1 = Alkali Metals Silvery appearance Soft enough to cut with a knife Vigorously reactive with nonmetals Also reactive with water and air – Group 2 = Alkaline Earth Metals Harder, denser, and stronger Higher melting points Still highly reactive

5. Hydrogen and Helium – Unique elements that do not have similar properties to groups 1 or 2, as their electron configurations would suggest

6. D-block elements: Groups 3-12 – Metals with typical metallic properties – Often referred to as transition elements – Good conductors of electricity – High luster – Typically less reactive than groups 1 and 2 – Some are so nonreactive that we find them as free elements in nature (Au, Pt, Pd)

7. p-block elements: Groups 13-18 – Together with the S-block elements, are called the main- group elements – Properties vary greatly – Includes all non-metals, all six metalloids, plus 8 p-block metals – Group 17 = halogens Most reactive nonmetals: react with metals to form salts – Group 18 = Noble Gases nonreactive – Metalloids (B, Si, Ge, As, Sn, Te) Brittle solids, some properties of metals, some of nonmetals Moderate conductivity (semiconductors)

8. F-block elements – Lanthanides Shiny metals React similarly to group 2 alkaline earth metals – Actinides All radioactive First 4 are found naturally on Earth The others are lab-made elements