1 / 12

The Evolution of the Periodic Table: Key Discoveries and Classifications

Chapter 5 explores the historical development of the Periodic Table from its inception in 1829 to modern classifications. Key milestones include Johann Dobereiner's Law of Triads in 1829, John Newlands' Law of Octaves in 1864, Dmitri Mendeleev's organization by atomic mass in 1869, and Henry Moseley's reordering by atomic number in 1914. The chapter delves into the periodic law, the arrangement of elements into periods and groups based on similar properties, and the characteristics of metals, nonmetals, metalloids, and various groups including alkali metals, halogens, and noble gases.

zenia
Télécharger la présentation

The Evolution of the Periodic Table: Key Discoveries and Classifications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Periodic Table Chapter 5

  2. History of the Periodic Table 1829 – Law of Triads, Johann Dobereiner • In a group of three elements with similar properties, the mass of the middle element is the same as the average mass of the other two elements 1864 – Law of Octaves, John Newlands • When the elements are listed in order by atomic mass, the properties of the eighth element are similar to the properties of the first element

  3. 1869 – Periodic Table of Elements, Dmitri Mendeleev • When the elements are listed in order of increasing ATOMIC MASS, they form rows and columns that showed a repeating pattern of properties * This allowed for the prediction of the properties of elements not yet discovered!! 1914 – Modern Periodic Table, Henry Moseley • Moseley identified the number of protons the elements have. The elements were rearranged in order of ATOMIC NUMBER (number of protons).

  4. periodic - having a regular, repeating pattern Examples: • days of the week • months of the year periodic law – The properties of the elements repeat in a predictable way when atomic numbers are used to arrange elements into groups.

  5. Arrangement of the Elements *Horizontal rows on the periodic table are called periods; the atomic number (number of protons) of the elements increases from left to right *Vertical columns on the periodic table are called groups; the members of each group have similar properties Valence electrons– electrons located in the outermost energy level of an atom, 8 valence electrons is considered “full”

  6. Three Classes of Elements Metals • Found to the LEFT of the zig-zag line • Contain few valence electrons • Lose electrons when form compounds • Good conductors of heat and electricity • Malleable (can be hammered into sheets) • Ductile(can be drawn into thin wires) • Shiny, most are silver

  7. Nonmetals • Found to the RIGHT of the zig-zag line • Outer energy level is nearly full; noble gases have full outer energy level • Gain electrons when form compounds • Dull • Not malleable or ductile • Brittle when in solid form • Poor conductors of heat and electricity

  8. Metalloids • Border the zig-zag line (B, Si, Ge, As, Sb, Te, Po and At) • Have some properties of metals and some properties of nonmetals • Semiconductors – depending on temperature • Outer energy levels are about half full • Can be shiny or dull • Usually brittle

  9. Characteristics of the Groups Group 1: Alkali metals • Contain 1 valence electron • Soft - can cut with a knife • Low density • Most reactive of all metals; never found pure in nature • React violently with water Group 2: Alkaline earth metals • Contain 2 valence electrons • Very reactive, but less reactive than group 1 • Harder and more dense than group 1

  10. Group 3 – group 12: Transition metals • Contain 1 or 2 valence electrons • Less reactive than groups 1 and 2 • Excellent conductors of heat and electricity • Higher densities than groups 1 and 2 Lanthanides (atomic numbers 58-71) • Part of transition metals, follow lanthanum, also known as “Rare Earths” • Reactive • Many used in alloys Actinides (atomic numbers 90-103) • Part of transition metals, follow actinium • All are radioactive (unstable) • All following plutonium (atomic number 94) are synthetic

  11. Group 13 – Group 16 • Mixtures of metals, metalloids, and nonmetals • Varied reactivity • Group 13 – 3 valence electrons • Group 14 – 4 valence electrons • Group 15 – 5 valence electrons • Group 16 – 6 valence electrons • No other consistent characteristics Group 17: Halogens • Consists of all nonmetals • Contain 7 valence electrons • Most reactive nonmetals • Poor conductors of heat and electricity • React violently with Alkali metals (group 1) to form salts • Never found as pure elements in nature

  12. Group 18: Noble gases • Consists of all nonmetals • Have a FULL set of valence electrons (2 electrons for helium, 8 for the rest) • Unreactive • Colorless, odorless gases at room temperature • Used in lighted signs because glow in color when electricity is run through them (neon is red, argon is lavender, helium is yellow, xenon is blue) Hydrogen • Contains 1 valence electron, so placed above group 1 (Alkali metals), but is NOT a metal • Very reactive • Reacts explosively with oxygen • Low density • Most abundant element in the universe (think stars)

More Related