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Honors Chemistry Chapter 6 The Periodic Table 6.1 Early Attempts @ Classification: Dobereiner & Newlands 1817 – Johann Dobereiner found Ca, Ba, & Sr had similar props ◦ Atomic mass of Sr was ~ midway betw Ca & Ba ◦ Grouped them into Triads Found several triads w/ similar props In ea triad, the middle elem had an atomic mass ~ ½ way betw the other 2 elems 6.1 Early Attempts @ Classification: Dobereiner & Newlands 1863 – John Newlands arranged elems in order of atomic mass ◦ Noted a repetition of similar props every 8th elem Called this the Law of Octaves 6.2 Mendeleev’s Periodic Table Dmitri Mendeleev – also put elems in a table ◦ Said props of elems were a function of their atomic masses ◦ Felt props occurred after periods varying in length 7 elems in 1st 2 periods, 17 elems in next 2 6.2 Mendeleev’s Periodic Table Mendeleev & Lothar Meyer, working separately, made an 8 column table of elems ◦ Mendeleev left blanks in table to group all elems w/ similar props in the same column Thought elems had yet to be discovered Predicted props & atomic masses of several elems Eventually discovered & his predictions were very close ◦ Said “props of elems are a periodic function of their atomic masses” – Periodic Law 6.3 Problems w/ Mendeleev’s Table When all elems were placed in order of incr atomic masses, Te & I were in the wrong columns ◦ If switched, they were in correct columns As more elems were discovered, other pairs were also switched 6.3 Problems w/ Mendeleev’s Table Henry Moseley found atomic number of many elems ◦ Result – periodic law was revised: The properties of the elements are a periodic function of their atomic number. 6.4 Modern Periodic Table Atomic # gives # of p+’s & # of e-’s Certain e- arrangements are repeated periodically ◦ Elems w/ similar e- configs are placed in the same column ◦ Can also list elems in the column in order of incr principal quantum # This forms the Periodic Table. Construction of Table: Align elems w/ similar outer e- configs ◦ 1st 2 elems fill 1st energy level & 1st row of table ◦ 3rd elem ends in 2s1 – similar to H – goes under it. ◦ Be – 2s2 – similar to He, but doesn’t fill energy level – does not go under it ◦ B thru Ne; have e-’s in p sublevel – new columns Ne fills 2nd energy level – goes under He Construction of Table: Na thru Ar fill 3rd energy level, make up 3rd row K & Ca begin 4th energy level – start 4th row 6.5 Transition Elements Sc begins to fill sublevel – starts new column Sc thru Zn fill sublevel & head new columns * Cr & Cu have 1 e- in highest energy level due to stability of ½ filled & completely filled sublevels Elements in columns 3-12 (IIIB – IIB) 6.5 Transition Elements Next 6 elems have e-’s in highest p sublevel ◦ Elems in column 18 have 8 e-’s in outer level (except He) ◦ Next e- begins a new row The Lanthanoids & Actinoids - Sometimes called Rare Earth Elements Lanthanoid Series – La thru Yb begin filling the 4f sublevel ◦ *Assume elems have predicted configs except for ½ filled & complete filled sublevels Actinoid Series – Ac thru No – fill 5f sublevel The Lanthanoids & Actinoids Both series are placed below the table Period – all elems in a horizontal row Group – all elems in the same vertical column 6.7 Octet Rule When s & p e-’s are in the highest energy level of an atom, they are in the outer level ◦ d & f e-’s can never be in outer level of neutral atom \ the largest # of e-’s in outer level is 8 ◦ These 8 e-’s are called an Octet. An atom w/ 8 e-’s in outer level is considered to have a full outer level 6.7 Octet Rule Octet Rule – an atom w/ 8 e-’s in their outer level is chemically stable ◦ He is also considered stable bec. Its out level is full Can only hold 2 e-’s It is sometimes possible to force the outer level of an elem in 3rd or higher period to hold more than 8 e-’s ◦ - Extended Octet Noble gas comps are formed this way Surveying the Table: Electron Configurations In the periodic table, elems w/ similar props are in a column An atom’s chemical props are determined by its e- config ◦ \ the periodic table is constructed on the basis of e- config Surveying the Table: Electron Configurations Elems in columns labeled “A” have their highest energy e- in an outer s or p sublevel ◦ The coef is the same as the # of the period Surveying the Table: Electron Configurations Elems in columns labeled “B” have their highest energy e- in a d sublevel, one level below the outer level ◦ The coef is 1 less than the period # Lanthanoids & Actinoids end in f1 – f14 w/ coef 2 less than the period # Full or ½ full sublevels are more stable than other arrangements 6.9 Metals & Nonmetals Groups 1 & 2 contain the most active metals Group 1 (except H) – Alkali Metal Family Group 2 – Alkaline Earth Metal Family 6.9 Metals & Nonmetals Nonmetals are on the right side of the table ◦ Group 16 – Chalcogen Family ◦ Group 17 – Halogen Family ◦ Group 18 – Noble Gases Metals – hard, shiny & conduct heat & electricity well Nonmetals – generally gases or brittle solids, dull, insulators 6.9 Metals & Nonmetals Elems are classified as metals or nonmetals on the basis of e- structure. ◦ Metals have few e-’s in outer level Tend to lose outer e-’s & form (+) ions when forming compounds ◦ Nonmetals have more e-’s in outer level Gain e-’s to form (-) ions when forming comps May also share outer e-’s w/ other atoms 6.9 Metals & Nonmetals General Rule: ◦ 3 or less e-’s in outer level – metals ◦ 5 or more e-’s in outer level – nonmetals Metalloids – elems which have props of both metals & nonmetals Stairstep line in table is a rough dividing line betw metals & nonmental ◦ Elems that lie along this line are usually metalloids 6.9 Metals & Nonmetals Groups 13-15 include both metals & nonmetals ◦ Top of ea group is nonmetallic ◦ Metallic character of elem incr toward the bottom of the table. 6.9 Metals & Nonmetals Metals are on the left side of table. Nonmetals are on the right side of table. Most elems are metallic. The most unreactive atoms are the noble gases ◦ Chemically stable bec of octet rule.