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5.1: History of the Periodic Table 5.2: Periodic Properties

5.1: History of the Periodic Table 5.2: Periodic Properties. Mendeleev. Noticed that when elements are arranged in order of increasing atomic mass, certain similarities in their chemical properties appeared at regular intervals

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5.1: History of the Periodic Table 5.2: Periodic Properties

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  1. 5.1: History of the Periodic Table5.2: 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

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