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Periodic trends – chapter 3.8 www.learner.org World of chemistry “the periodic table” watch online.

Periodic trends – chapter 3.8 www.learner.org World of chemistry “the periodic table” watch online. Definition Periodic— Varying in a systematic and repetitive way. Knowing the position of an element in the periodic table reveals much information about its chemical and physical properties.

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Periodic trends – chapter 3.8 www.learner.org World of chemistry “the periodic table” watch online.

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  1. Periodic trends – chapter 3.8www.learner.orgWorld of chemistry “the periodic table” watch online. Definition Periodic— Varying in a systematic and repetitive way

  2. Knowing the position of an element in the periodic table reveals much information about its chemical and physical properties Chemical properties way it reacts with other elements due to (i.e., the way it behaves to complete its octet) Physical properties Any characteristic besides the way it reacts e.g., density, atom size, electrical conductor,

  3. Trends you’ll need to know and explain Atomic radius First ionization energy Reactivity to form + ions Reactivity to form - ions Electronegativity Metallic nature Oxidation number Valence electron number

  4. Trends in valence electron number • The trend that underlies all the others!

  5. Why do these periodic trends exist? Members of families have the same number of valence electrons & so also similar chemical properties. Members of the same period are adding electrons to the same valence shell (& same inner shell d or f orbitals), so they have similar distance between the nucleus and valenceshell. http://www.eserc.stonybrook.edu/ProjectJava/ChemicalChargeApplet/valence_fig1.gif

  6. Except for the noble gases, atoms need to either lose, gain, or share electrons to have a stable valence shell (highest energy level s & p orbital octet)

  7. Valence electrons control chemical properties The octet rule explains why: Atoms are most stable when they possess a filled valence (outermost) shell octet. (i.e., when their outermost energy level—highest energy level—contains a total of 8 electrons in s and p orbitals. Members of group 18 (the noble gases—aka inert gases) have highest stability and are the only atoms commonly found unbonded. Inert means nonreactive.

  8. A Lewis dot structure (electron dot structure) shows only the valence electrons of an atom. In the s and p blocks, all members of the same group/family (columns) have the same number valence electrons, but these are in different energy levels (shells). In each period (row), all elements have valence electrons located in the same energy level (shell).

  9. Transition metals families may show variable # s orbital valence electrons Most members of d & f block families(called transition metals) also have same #s valence electrons. Exceptions occur in cases where skipping one or both valence s orbital electron positions allows for greater stability: • some d & f partial filled configurations are more stable than others • half & fully filled d & f orbitals are particularly stable. Mo [Kr] 5s1 4d5Ag [Kr] 5s1 4d10 Au [Xe] 6s1 4f14 5d10 Mo° Ag ° Au ° Not all tr metals violate filling rules Os [Xe] 6s24f145d6 Os:

  10. Lewis dot structures of the “representative elements” shows a periodic trend. Stays the same within the family, but increases moving right in a period.

  11. Trends in electronegativity: • The trend that controls HOW an element will react to become more stable and obey the octet rule for valence electrons. electronegativity (property indicating how tightly an atom would pull electrons toward itself in a bond with another atom).

  12. Electronegativity is rated on a scale from 0 to 4.0

  13. Metals have low electronegativity (property indicating how tightly an atom would pull electrons toward itself in a bond with another atom). So, metals form + ions by giving away valence shell electrons, exposing filled inner shell s & p orbitals.

  14. Nonmetals have high electronegativity. So, nonmetals form – ions by taking valence shell electrons to fill their existing valence shell. Lowest for Francium: 0.7

  15. Trends in electronegativy: increases left to right, decreases top to bottom. http://lhs2.lps.org/staff/sputnam/chem_notes/UnitII3.gif

  16. Trends in oxidation numbers • Reflects the electronegativity of the element and its valence electron number, as well as its ionization energy (opposite of electronegativity)

  17. The oxidation number of an element is the charge its atoms attain when forming stable ions that satisfy the octet rule.Metalloids alter strategy according to bonding partners. If bonding to an element with much lower electronegativity, the nonmetal will adopt the – oxidation number. If bonding to an element with much higher electronegativity, they will adopt the positive oxidation number. If bonding to a partner of similar electronegativity, they will form covalent bonds, sharing electrons.

  18. Oxidation numbers of the “representative elements” shows a periodic trend. Stays the same within the family, but changes moving across periods.

  19. As electrons are added to the same shell, and as proton #s are simultaneously increasing at the same distance from the nucleus, electrons are pulled more tightly towards the nucleus. As valence electrons are added to higher energy levels (shells), atomic radius increases. So average atomic radius Decreases moving right within a period & Increases moving down Each family. http://www.camsoft.co.kr/CrystalMaker/support/tutorials/crystalmaker/resources/VFI_Atomic_Radii_sm.jpg

  20. In family 1 (alkali metals) a single valence electron in an s orbital is located progressively farther from the nucleus as the elements are placed in progressively lower periods.This means that the higher an element is located in a period, the more tightly held the valence electron is attracted to the nucleus; that is, the higher its electronegativity. http://www.grandinetti.org/Teaching/Chem121/Lectures/Electronegativity/assets/ElectronegativityTrends.gif http://www.bbc.co.uk/scotland/learning/bitesize/higher/chemistry/images/patterns_fig04.gif

  21. Electronegativity decreases as valence electrons are added to progressively higher energy shells because valence electrons become progressively more shielded. So, the valence electron of K is more highly shielded than the valence electron of Na, and the valence electron of Na is more highly shielded than the valence electron of Li. The electrons of the inner shells compete more strongly for the proton’s positive charges.

  22. Having lower electronegativity & lower shielding results in higher energy levels valence electron being lost more easily. During chemical reactions creating ions, nonmetal atoms pulling on metal atoms’ valence electrons expend less energy freeing valence electrons from higher energy levels than from lower energy levels. First ionization energy (energy to remove the 1st valence electron from an atom) decreases going downward in a group/family. http://www.grandinetti.org/Teaching/Chem121/Lectures/PeriodicTrends/assets/IonizationTable.gif

  23. First ionization energy decreasesmoving down families, but increases moving right in periods. This is because more proton charges exert more attractive force on the same valence shell electrons.

  24. Less energy is needed to remove K’s s valence electrons than to remove Na’s. That is, K—farther down the alkali metal family—has lower first ionization energy. That’ why it’s more reactive than Na.

  25. Watch these videos that show how reactivity of metals (to form + ions) is related to position in the periodic table Alkali metals http://www.youtube.com/watch?v=QSZ-3wScePM http://www.youtube.com/watch?v=SjowQJMS-W4&NR=1&feature=fvwp Note the comments on “Fr bomb”—what do you think?

  26. Tendency to form negative ions increases as you move right in a period, except for the noble gases which are not reactive. That is because the valence shell is close to the nucleus whose electrons have higher and higher attraction for the valence shell.Tendency to form negative ions decreases going down a period since the protons are so shielded from the valence shell.Fluorine has the highest tendency to form negative ions of any element, and francium has the lowest tendency to form negative ions. • http://video.google.com/videosearch?sourceid=navclient&rlz=1T4ADSA_enUS350US350&q=reactivity%20halogens&um=1&ie=UTF-8&sa=N&hl=en&tab=wv#

  27. Metallic Nature increases moving right to left in a period and moving high to low in a family The farther left you go in a period, the more “metallic” the properties of an element: • the more lusterous (shiny) • the more ductile (can be pulled into wires) • the more malleable (can be hammered to sheets) • The less brittle • The more highly conducting of heat • The more highly conducting of electricity • The less electronegative (the less tightly it attracts its valence electrons to its nuclear protons. • The more reactive in its ability to form ionic compounds with nonmetals

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