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Understanding the Periodic Law: Historical Discoveries and Key Trends

This chapter explores the evolution of the periodic law, highlighting major contributions from scientists like Cannizzaro, Mendeleev, and Moseley. Cannizzaro's 1860 method for determining atomic masses allowed for the organized classification of elements, while Mendeleev's 1869 periodic table arranged elements by mass and properties, predicting the existence of undiscovered elements. Moseley's 1911 work with X-rays led to the modern arrangement of the periodic table based on atomic numbers. Key trends such as atomic radius, ionic radius, and the formation of ions are also discussed.

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Understanding the Periodic Law: Historical Discoveries and Key Trends

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  1. Chapter 5 The Periodic Law

  2. History • Cannizzaro- 1860 • presented a new method for determining mass of elements • gave scientists a way to organize elements

  3. History • Mendeleev-Russian 1869 • organized elements according to mass and properties • noticed that properties repeated periodically • predicted elements, later identified as Sc,Ga,Ge

  4. History • Moseley-1911 • Used X-rays for determining the # of protons • This is how our current periodic table is arranged.

  5. Periodic Law • Physical and chemical properties repeat periodically if arranged according to atomic number. Recurring or reappearing from time to time; intermittent. http://www.thefreedictionary.com • Look for overall patterns- may see some variation.

  6. History • Changes since Moseley • Noble gases-Ramsay • Lanthanides/Actinides- Seaborg

  7. The Periodic Table Trends

  8. Atomic Radius • tells us the size of the atom • measured using ½ the distance between the nuclei of identical atoms bonded together

  9. Atomic Radius • TREND: • going across the atoms get smaller • going down the atoms get larger

  10. Ionic Radius • tells us the size of the ion • positive or negative atom because of loss or gain of electrons • Cation-positive ion • Anion-negative ion

  11. Ionic Radius • Cations are smaller than the parent • Lose electrons

  12. Ionic Radius • Anions are larger than the parent. • Gain electrons.

  13. Ion Formation • Why do ions form? • Atoms try to become stable. • Achieve a noble gas configuration. • Become isoelectronic with noble gases • Having the same electron configuration

  14. Ion Formation • Examples: • Calcium • Nitrogen

  15. Ion Formation • You try these: • Potassium • Iodine • Aluminum

  16. Ionization Energy • Amount of energy required to remove an electron from an atom

  17. Electron Affinity • energy change when an electron is added to an atom • energy release means it is easier to add e- • opposite of ionization energy

  18. Electronegativity • measure of the ability of an atom to attract electrons when it is bonded to another atom • Think: sharing with a partner, equal sharing or unequal sharing

  19. Table of Electronegativities

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