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Chapter 6 – Periodic Table

Chapter 6 – Periodic Table. Development of the Periodic Table In 1829. Li   Na  K         Cl   Br   I 7     23     39           35    80   127. Ca   Sr   Ba     (40 + 137) ÷ 2 = 88 40     88     137. Dobereiner proposed the Law of Triads :

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Chapter 6 – Periodic Table

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  1. Chapter 6 – Periodic Table

  2. Development of the Periodic TableIn 1829 Li   Na  K         Cl   Br   I7     23     39           35    80   127 Ca   Sr   Ba     (40 + 137) ÷ 2 = 8840     88     137 Dobereiner proposed the Law of Triads: The middle element in the triad (group of 3 elements) had atomic weight that was the average of the other two members

  3. In 1863 Law of Octaves John Newlands proposed The Law of Octaves: When elements are arranged in increasing atomic mass the 1st & 8th elements exhibit similar behavior. This behavior repeats in a periodic fashion Little attention was paid to Newlands work because he linked his finding to music.

  4. Dmitri Ivanovich Mendeleev & Lothar Meyer In 1869 & 1871 • Mendeleev's periodic table was arranged with increasing atomic weight and attention to chemical properties. • Periodic Table contained columns (groups) & rows (periods). • Mendeleev left gaps in the table. • He predicted the discovery of new elements that would fill these gaps.  • eka-aluminum, eka-boron, and eka-silicon • Gallium, Scandium and Germanium • Later in 1869 German Chemist Lothar Meyer indepently published a nearly identical table • In 1906, Mendeleev came within one vote of receiving the Nobel Prize in chemistry “I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.”--Mendeleev, Principles of Chemistry, 1905, Vol. II

  5. In 1914 Moseley's Periodic Law • It starts with Rutherford's landmark Gold Foil Experiment discovering the proton in 1911 • Henry Moseley was able to derive the relationship between x-ray frequency and number of protons. • Moseley Periodic Law arranges the elements according to increasing atomic numbers and not atomic masses, • some of the inconsistencies associated with Mendeleev's table were eliminated. • The modern periodic table is based on Moseley's Periodic Law (atomic numbers). • At age 28, Moseley was killed in action during World War I

  6. In 1940 The last major change • Glenn Seaborg discovered the Inner transition metals transuranium elements 94 to 102 • This reconfigured the periodic table by placing the lanthanide/actinide series at the bottom of the table. • In 1951 Seaborg was awarded the Nobel Prize in chemistry and element 106 was later named Seaborgium (Sg) in his honor.

  7. IUPAC 1 18 American 1A 2 13 14 15 16 17 8A European IA 2A 3A 4A 5A 6A 7A VIIIB IIA IIIB IVB VB VIB VIIB 3 4 5 6 7 8 9 10 11 12 3B 4B 5B 6B 7B ----------8B------- 1B 2B IIIA IVA VA VIA VIIA ------VIIIA------- IB IIB Groups by NUMB3RS Group or Family – Vertical columns on the PT Period – Horizontal rows on the PT

  8. Metals • Most elements are metals. • 88 elements found to the LEFT of the Zigzag Line • Physical Properties of Metals: • Luster (shininess) • Good conductors of heat and electricity • High density (heavy for their size) • High melting point • Ductile (drawn out into thin wires) • Malleable (hammered into thin sheets) • Chemical Properties of Metals: • Easily lose electrons (positive ions CATIONS) • Corrode easily

  9. Nonmetals Nonmetals are found to the RIGHT of the Zigzag Line Characteristics are opposite those of metals. Physical Properties of Nonmetals: Poor conductor of heat Poor conductor of electricity No luster (dull appearance) Brittle (breaks easily) Not ductile Not malleable Low density Low melting point Chemical Properties of Nonmetals: Tend to gain electrons   (negative ions ANIONS) 

  10. Metalloids • Elements on both sides of the Zigzag Line • have properties of both metals and nonmetals • Physical Properties of Metalloids: • Solids • Can be shiny or dull • Ductile • Malleable • Conduct heat and electricity better than nonmetals but not as well as metals

  11. Background Vocabulary before we start talking about Periodic Trends • Valence Electrons • Effective Nuclear Charge • Electron Shielding

  12. Valence Electrons • The valence electrons are the most important electronsin the formation of chemical bonds. • The number of valence electrons for an atom is equal to the number of electrons in the outermost energy level • All elements in the same group have the same number of valence e- • The number of valence electronsis equal to the A group number on Periodic Table • (American numbering)

  13. Valence Electrons - Examples • Boron electron configuration is 1s2 2s2 2p1 • so the outer energy level is 2, • there are 2+1 = 3 electrons in level 2. • These are three valence electrons! • Boron is in group 13 or 3A – 3 valence electrons • Bromine electron configuration is [Ar] 4s2 3d10 4p5How many valence electrons are

  14. Effective Nuclear Charge • The charge felt by the valence electrons after taking into account shielding.

  15. Electron Shielding • The reduction of the attractive force of the nucleus for the outer electrons • caused by electrons in energy levels between the nucleus and the outer electrons

  16. Periodic Trends

  17. Atomic Radius Since a cloud’s edge is difficult to define, scientists use covalent radius, or half the distance between the nuclei of 2 bonded atoms. Atomic radii are usually measured in picometers (pm)1x10-12 or angstroms (Å). An angstrom is 1 x 10-10 m.

  18. Atomic Radius Trend • DOWN A GROUP = Atoms get larger • Higher energy levels have larger orbitals • ACROSS A PERIOD Left to Right Atoms get smaller • Increased nuclear charge without additional shielding pulls e- in tighter • Each step adds a proton an electron (1 or 2 neutrons) • Electrons are added to existing energy levels or sublevels. The effect is that the more positive nucleus has a greater pull on the electron cloud making the atom smaller.

  19. Ionization Energy • The energy required to remove an electron from an atom. (measured in kilojoules, kJ) • The larger the atom is, the easier it is to remove its electron. • Larger atoms have weaker nuclear charge holding the outer electrons thus have lower ionization energy Ionization energy and atomic radius are inversely proportional.

  20. Ionization Trend • DOWN A GROUP Ionization Energy Decreases • It becomes easier to remove an electron the further it is way from the nucleus • ACROSS A PERIOD Left to Right Ionization Energy Increases • It becomes harder to remove an electron because e- are pulled closer to the nucleus as you move across the group • Nobel gasses have the highest Ionization Energy because they are stable with a full set of valence electrons.

  21. Ionic Radius • Cations • Positive Ions – metals • Lost electrons • Cationsare always smaller than the original atom. • The entire outer energy level is removed during ionization • Anions • Negative Ions – Nonmetals • Gain Electrons • Anions are always larger than the original atom. • Electrons are added to the outer energy level during ionization.

  22. Electronegativity • Electronegativity is a measure of an atom’s attraction for another atom’s electrons. • It is an arbitrary scale that ranges from 0 to 4. • The units of electronegativity are Paulings. • Generally, metals are electron givers and have low electronegativities. • Nonmetals are areelectron takers and have high electronegativities.

  23. Electronegativity Trend • Nobel Gasses are stable because they have a full set of valence e- • Nobel gasses have 0 Paulings – electronegativity • Except Kr & Xe • Fluorine is the most electronegative element • Down a group – electronegativity decreases • Across a period (L to R) - electronegativity increases

  24. Electron Affinity • The energy given off when atom gains an extra electron • This trend is very similar to electronegativity • Think of it like electronegativity … It still has to do with attraction for electrons.

  25. Overall Reactivity • This ties all the previous trends together in one package. • However, we must treat metals and nonmetals separately. • The most reactive metals are the largest since they are the best electron givers. • brainiac alkali metals • The most reactive nonmetals are the smallest ones, the best electron takers.

  26. 0 Overall Reactivity • Your help sheet will look like this:

  27. Metallic Character • This is simple a relative measure of how easily atoms lose or give up electrons. • Your help sheet should look like this:

  28. Melting/Boiling Point • Melting/Boiling Point • Highest in the middle of a period.

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