Chapter 6 Periodic Law and Periodic Table

Historical background  Before 1800, 23 elements known  By 1870, 70 elements identified  No pattern to tie them together known  1864, J. Newlands noticed when elements arranged by mass  1 st and 8 th element similar  2 nd and 9 th element similar, so on.  He called pattern an octave. Did not work for all.

Mendeleev  Noticed patterns while writing a book on elements.  Noticed that as mass increased, there is a repeating of characteristics of elements.  Also realized that some elements were not discovered yet.  Predicted properties of those, and was found to be correct when discovered.

 Were some trouble spots on P.Table (Te,I)  Accdg. to Mendeleev, Periodic law stated that the characteristics of the elements were a periodic (repeating) function of their atomic masses.

Moseley  Discovered the proton.  Called the #protons the atomic number.  Realized this could “fix” Mendeleev’s P.T. problems.  This changed P. Law to be based on atomic number, not mass.(Te, I switched)  “Chemical and Physical properties repeat (are periodic) when arranged by at. no.”

Modern Periodic Table  Has columns and rows of elements.  Columns are GROUPS or FAMILIES  Very similar in chem and phys. activity  Not identical, though.  Rows are called PERIODS  Elements in a period are not at all alike.

Classification of elements

Metals  Left and middle of P. Table  Majority of elements  Shiny (lustrous)  Good conductors of heat and electricity  Malleable  Ductile  GR. IA alkali metals-most reactive  GRIIB alkaline earthmetals, less reactive

Group B Elements transition elements  Transition metals  Families 3-12 on PT  Inner Transition Metals  Lanthanide Series 4f block  Actinide Series 5f block

Nonmetals  Upper right of PT.  P block  Group 7A halogens  very reactive  Need to gain 1 e -  Group 8A noble gases  Very unreactive  Filled levels

Metalloids  Border of stair step line on PT.  Have phys. & chemical characteristics of both metals and nonmetals

Write E config of Main Groups  These groups or families of elements have similar phys. and chem. characteristics.  Reason is found in their e - config. They are so similar to each other.  Same number of valence (outer) e - cause similar reactivity.

S block  Group IA, IIA  Group IA [ ]s 1 config.  Only 1 outer e -  That e - easily lost  Very reactive (most of all metals)  Alkali metals

 Group 2A alkaline earth metals  2 outer e -  Fairly easily lost, fairly reactive  Config. ends in s 2 (those lost)

P block Elements  3A through 8A families (IIIA-VIIIA)  Have filled or partially filled orbitals  Have various reactivity depending on number of outer e -  8A (noble gases)  Very stable  Very UNreactive  Don’t need any more e -, levels filled

D Block Elements  Transition metals  Largest block  Have filled outer s orbital and filled or partially filled d orbitals.

F block Elements  Contain inner transition metals  Have filled outer s sublevel and filled or partially filled f orbitals  Number of orbitals and e - held:  Sblock 1 orb/level, up to 2e in each  P block, 3 orb/level, up to 6e total in each levl  D block, 5 orb/level, up to 10 e total in each  F block, 7orb/level, up to 14 e total in each

Periodic Trends Graphing Calc Activity  Many properties or characteristics of elements change in predictable patterns.  Atomic Radius  Direct measure of atom’s size.  Atoms get smaller L→R on P.Table  Because more pro + are added to nucleus to pull more tightly on e cloud.  Atoms get larger  because more levels of e are added to outside. (Onion and layers)

Ionic Radius  Atoms gain or lose e to have only filled levels  These + or – particles that result are IONS.  Ions will have the same no. pro + as atom of that element. (Only e change)  The more e added to an atom, the larger the ion will be.  The more e lost, the smaller the ion.

 S _2 larger than S atom. (18 e/16e)  Cl - larger than Cl. (18e/17e)  Na + smaller than Na atom. (10e/11e)  Mg +2 smaller than Mg atom (10e/12e)

Ionization Energy  Amount of energy needed to pull off the outer e from an atom. (produces a + ion)  Atoms on Left of P.Table hold their e loosely and easily lose them.  Atoms on Right (P Block) of P.T. hold e tightly because they would rather gain than lose e.  I.E. increases L→R

 I.E. decreases  because as atoms get larger the outer e are further from the nucleus and attraction from pro +.

Octet Rule  We have hinted at this idea-  Atoms tend to gain, lose, or share e to obtain a full set of 8 outer e (s and p blocks)  H and He are filled with 2 e, no p block at all.

Electronegativity  Ability of an atom to attract e to itself within a chemical bond.  Arbitrary units assigned to elements up to 3.98 (F is most e negative )  Cs and Fr (opp corner from F) are least.  Whichever element in bond has largest value pulls e more toward itself. (E greedy)  EN inc→, EN dec .